Can mutation take place in G1 and G2 phases during the cell cycle?

Can mutation take place in G1 and G2 phases during the cell cycle?

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We know that the DNA replicates during the S phase in Interphase. There it might undergo a number of mutations. We also know that the forward half strands are more susceptible to undergoing a mutation since they live most of their lives single-stranded. But can mutation take place anytime before or after the replication? It is weird that the strands "wait" to open up in the S phase and only then undergo a mutation.

Yes, it can. A mutation can potentially occur at any given moment in the cell cycle, not only in S phase, which is why revision mechanisms remain alert during the whole cycle. Such mechanisms not only make sure every important event in the cycle takes place adequately (e.g. DNA replication, chromosome segregation) but also repair any damage associated with DNA (e.g. AP sites, single strand breaks, double strand breaks, to name a few). Once DNA damage takes place, specialized sensors detect such events and activate several mechanisms. One of these will pause the progression of the cell in the cell cycle, and another will repair the DNA-associated damage, in case that it can actually be repaired [1].

[1] Karp, G. (2009). Molecular and Cellular Biology: Methods and Concepts. Wiley. New York.

Impact of 9p deletion and p16, Cyclin D1, and Myc hyperexpression on the outcome of anaplastic oligodendrogliomas

To study the presence of 9p deletion and p16, cyclin D1 and Myc expression and their respective diagnostic and prognostic interest in oligodendrogliomas.


We analyzed a retrospective series of 40 consecutive anaplastic oligodendrogliomas (OIII) from a single institution and compared them to a control series of 10 low grade oligodendrogliomas (OII). Automated FISH analysis of chromosome 9p status and immunohistochemistry for p16, cyclin D1 and Myc was performed for all cases and correlated with clinical and histological data, event free survival (EFS) and overall survival (OS).


Chromosome 9p deletion was observed in 55% of OIII (22/40) but not in OII. Deletion was highly correlated to EFS (median = 29 versus 53 months, p<0.0001) and OS (median = 48 versus 83 months, p<0.0001) in both the total cohort and the OIII population. In 9p non-deleted oligodendrogliomas, p16 hyperexpression correlated with a shorter OS (p = 0.02 in OII and p = 0.0001 in OIII) whereas lack of p16 expression was correlated to a shorter EFS and OS in 9p deleted OIII (p = 0.001 and p = 0.0002 respectively). Expression of Cyclin D1 was significantly higher in OIII (median expression 45% versus 14% for OII, p = 0.0006) and was correlated with MIB-1 expression (p<0.0001), vascular proliferation (p = 0.002), tumor necrosis (p = 0.04) and a shorter EFS in the total cohort (p = 0.05). Hyperexpression of Myc was correlated to grade (median expression 27% in OII versus 35% in OIII, p = 0.03), and to a shorter EFS in 9p non-deleted OIII (p = 0.01).


Chromosome 9p deletion identifies a subset of OIII with significantly worse prognosis. The combination of 9p status and p16 expression level identifies two distinct OIII populations with divergent prognosis. Hyperexpression of Bcl1 and Myc appears highly linked to anaplasia but the prognostic value is unclear and should be investigated further.

Citation: Michaud K, de Tayrac M, D’Astous M, Paquet C, Gould PV, Saikali S (2018) Impact of 9p deletion and p16, Cyclin D1, and Myc hyperexpression on the outcome of anaplastic oligodendrogliomas. PLoS ONE 13(2): e0193213.

Editor: Renato Franco, Seconda Universita degli Studi di Napoli, ITALY

Received: October 9, 2017 Accepted: January 20, 2018 Published: February 28, 2018

Copyright: © 2018 Michaud et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper.

Funding: This work was supported by grants from Fondation du CHU de Québec (grant #2885) to SS. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.


What exactly is “precision oncology,” and how can we, as a community, contribute to it? Despite its captivating terminology, the concept is not new after all, it has long been known that to be effective, specific ailments necessitate tailored treatments [1]. However, its current genomic basis distinguishes it from its outmoded cellular renditions [2, 3]. The term “precision medicine”,or “precision oncology,” as in our case here, is commonly used when the treatment strategies involve targeted therapies that are based on personal data from next-generation sequencing [4�]. That is, rather than select therapies based on the perceived type of cancer, for example, tissue or organ location, therapeutic selection is based on analysis of the individual’s genomic sequence and the specific identified mutational aberrations [15�]. It is the mutation-guided therapeutics, rather than the traditional cancer type-dependence classification, such as that based on classical anatomy and histology, that has etched a new context into this terminology. This concept has compelled a paradigm shift. Now patients with BRAF V600E mutations would be prescribed the same drug regimen irrespective of their cancer type and location, for example, acute myeloid leukemia, breast cancer, or melanoma [19].

Precision oncology was not always based on the individual’s genomic sequence. Since its inception, exactly what precision oncology includes has been unclear. In 2015, Collins and Varmus proposed that blood-typing�sed targeted therapies and immune therapy be included [20]. A 2017 analysis revealed that in the literature, “precision oncology” appears to have undergone an evolution [21]. Early on, therapies were disease and/or protein targeted, such as, for example, vascular endothelial growth factor (VEGF) inhibitors and Bcr-abl1 tyrosine kinase inhibitors (TKIs), bevacizumab (Avastin) and imatinib, respectively. Later, precision oncology treatments were referred to as selections of therapies based on analyses of biomarkers. Examples include crizotinib (Xalkori) in lung cancer with EML4-ALK rearrangements or adjuvant chemotherapy as in the Oncotype DX panel in breast cancer. The literature analysis observed that, only as of January 2016, precision oncology therapeutic selection appears to have been primarily based on next-generation sequencing data. As noted by Tsang and colleagues, various terms have been used to relate to precision genomic oncology, including simply precision oncology [22], genomics-driven oncology [23], genomic oncology, and personalized cancer medicine. All refer to high-throughput sequencing to inform clinical decisions at the point-of-care [24].

Even though the conceptual foundation of precision oncology is rational, thus stimulating broad enthusiasm, its current lack of demonstrated clear breakthroughs in clinical trials argues that in addition to more patient sequence data, critical components may be missing. Next-generation sequencing of patients with advanced cancers showed that less than 10% have actionable mutations [25, 26], and a randomized trial of precision medicine [27] did not observe improved outcomes with genome-based precision oncology. The biological complexity underlying target identification is challenging. The breakthrough of the next-generation sequencing delivered a new precision component: treatments might be tailored, not only to a certain illness but also to a specific person’s genetic make-up. This notion of prescribing “the right drug to the right person at the right time” [28�] has stimulated considerable research efforts, which have been pushed to the fore by the Precision Medicine Initiative (also called All of Us Research Program). But to date, it seems to still fall short, and the magnitude of the task is daunting. The mutational landscape is highly heterogeneous and challenging to decipher. Data indicate that the least mutated cancers have on average 0.28 mutations per megabase, with most presenting 8.15 mutations per megabase [21, 33]. Whole-exome analysis of pancreatic cancer, which is considered only moderately mutated, indicates 2.64 mutations per megabase. Further disconcerting is the low consistency among mutated genes. For example, certain mutations are observed fairly rarely in pancreatic cancer and are observed in other tissues as well [34]. Additional factors tied to cancer and individual complexities cast long and formidable shadows as well.

Therefore, even though it is broadly believed that precision oncology can improve treatments and prognosis, and that precision data are essential for precision oncology, the consensus is that this may not be enough [35]. Current clinical results do not question the sequence-based hypothesis and strategies, but they do emphasize the need for considering their completeness [36]. The literature thrives with proposed additional clinical considerations, and vital statistical and network tools are also being developed [37, 38]. One powerful element that we believe is missing is the energy landscape biomolecules are not static sculptures but interconvert between structures with varying energies [39]. Therefore, on its own, genomic sequence data may not provide the entire information to the oncologist in target selection. If the mutations are in protein coding regions, which is our focus here, then they translate to dynamic protein conformational ensembles and interactions, which in principle, we, as a community, can exploit to accomplish more accurate prognosis.

The low consistency among mutated genes in cancer argues that only translating sequence alterations to heterogeneous ensembles may not be sufficient, and new concepts should be brought to bear. One of these [40] is the notion that we should not only rely on classical categories and definitions of passenger mutations (appearing to confer no survival advantage) and driver actionable mutations (which propel cancer initiation and progression) [41�]. Passenger mutations whose effects on their own appear insignificant may transform into driver mutations when acting in certain combinations. We dubbed such mutations latent drivers [49]. The low consistency of mutations among genes also argues that focusing on single proteins may be lacking. Additionally, mutations can take place during cancer evolution within the same or different tissues [50].

Cancer disrupts normal physiological tissue homeostasis due to loss of function or gain of function, which can take place in multiple ways [51�]. Even though the underlying tenet of precision oncology largely rests on the notion that reversing one target will halt cancer, parallel signaling pathways leading to the same cellular outcome, compensatory mutations, and more are not overlooked. These are taken up through combinatorial drug regimens.

The excellent literature reviews and research papers in this area cover clinical and social benefits, as well as genomic sequence analysis, pattern identification, and approaches and/ or corroboration of target discovery. This latter category produces vital software tools [83�]. Recently, functional advances were reviewed as well [97]. Below, following a background, we relate to precision oncology from a different standpoint. Our premise is the sensitivity of the free energy landscape to its environment [98�]. We view actionable mutations within this framework, as well as their consequences for cell-specific signaling networks, and finally, we comment on how our community can help.

Where is the TERT gene located?

Cytogenetic Location: 5p15.33

Molecular Location on chromosome 5: base pairs 1,253,166 to 1,295,046

Figure- 4
The TERT gene is located on the short (p) arm of chromosome 5 at position 15.33.

More precisely, the TERT gene is located from base pair 1,253,166 to base pair 1,295,046 on

By this way, The Telomerase enzyme, synthesizing new Telomere at the end of DNA strands, prevents erasing of DNA codes in each cell division, up to a certain age limit.

How Telomerase synthesizes Telomere has been shown clearly in the videos below from 1-6.

5) genetic home, TERT GENE-chr-5


7) Claimed products to activate telomerase

Chapter-6, what is DNA? Mitosis Cell Division (1)

[ ইংরেজীতে প্রকাশিত করা হল কিছু কিছু বাংলাদেশী বংশোদ্ভূত বিদেশে অবস্থানরত ছাত্র পাঠকেরা যারা বাংলা ভাষা পড়তে পারেনা, তাদের অনুরোধে,দুখিতঃ]

The photo of Walther Flemming, the discoverer of Mitosis Cell Division.

Mitosis is a little part of Cell Cycle and the name of a type of Cell Division.

There is another type of cell division called Meiosis. At first Mitosis will be discussed.

Before starting Mitosis, The cell replicates or copies the pair of Chromosome that is called HOMOLOGOUS CHROMOSOME, one coming from mother and another from father, in Nucleus, into exact copies. (8) (See chapter 4 for Replication).

Now this copied Chromosome and the parent Chromosome are called “CHROMATID” for one another. (1) (See figure-2)

[Description of figure 2

In the figure, the sign “1” is a Chromatid it is an identical copy of the Chromosome that appears while cell is dividing. It is also called Sister Chromatid. The point where they are joined is called Centromere marked as sign “2’. They form separate individual new Chromosome while they detach from one another at Anaphase stage during Mitosis. Centromere has divided the Chromatid into 2 arms. A short arm called “P” arm that is marked here with sign “3” in left Chromatid, and a long arm called “q” arm that is marked here with sign “4” In Right Chromatid.]

Then the cell divides into nearly 2 equal sizes of new cells along with the divided Chromosome, organelle, Cytoplasm and cell wall. The genetic information of the parent cell and of 2 divided cells remain exactly same. The complete division of cell wall is called Cytokinesis. This process occurs in Eukaryotic (multicellular) organism and animal (2). Mitosis occurs at the M phase of cell cycle that is 10% of the total cycle (3). (See the description of cell cycle at Chapter 4).

The scientists believe that only unicellular organism (PROKARYOTES) existed upon this planet more than a billion (1,০০০,০০০,০০০) years. Their generations spread through direct binary fission. Later this binary fission transformed into Mitosis and Meiosis when EUKARYOTES appeared through evolution.

Walther Flemming ( April 21,1843- August 4,1904) was a German biologist and the founder Cytogenetics (Figure-1)

Cytogenetics is called that branch of biology which describes about Chromosomes and genetics of Nucleus.

He earned graduation in Medicine at University of Rostock 1n 1868. Then he served as army medical officer from 1870 to 1871 in the war field of France- Russian war. After that he served as a teacher at University of Prague from 1873 to1876. Then he joined as professor of Anatomy at University of Kiel in 1876. There he promoted up to Director of Anatomy Institute and continued up to death.

In this Institute he succeeded in observing and illustrating the Mitosis Division of cell. The result of his research was published first in 1878 and 1882 in Seminal Book Zellsubstanz, Kern und Zelltheilung.(4)

Relation between Mitosis and the development of embryo.

The unicellular ZYGOTE grows while a sperm joins and fertilizes an ovum at the Fallopian tube of Uterus. (See figure 3)

Figure 3, the unicellular ZYGOTE.

This unicellular ZYGOTE growing through mitosis and with cell differentiation develops as embryo in Uterus. It grows as baby after remaining 9 months and 10 days in Uterus. Later we grow as a mature human of about 100 Trillion (100,000,000,000,000) of cells.

All of these developments occur only through cell cycle and Mitosis.

Mitosis occurs in all somatic cell (those are not sex cells) like skin, heart, brain bone, Liver, Pancreas etc.(5)

Meiosis occurs only in male and female germ cells.

In Mitotic division, the divided new cell becomes same diploid cell as like parent cell. That is, in both parent cell and in new cell the number of Chromosome remains 23 pairs. In this pair one comes from father and another from mother and this pair is called HOMOLOGOUS CHROMOSOME (8).

But the male and female sex cells become HAPLOID cell due to Meiotic division that is, in sperm and ovum remain only 23 Chromosomes in place of 23 pairs. For this, they are called HAPLOID cell.

In sex cells, there remains no pair of Homologous Chromosome, but when they form Zygote, it forms a diploid cell containing 23 pairs of Chromosome.

This Zygote develops into a mature human of about 100 trillions of cells, and each of these cells contains the exactly same DNA.

For this, the Mitotic Division is the only way to grow a human body and has a great importance.

It has been divided into 5 phases-


Cytokinesis is considered as a separate phase.

Since Mitosis is a long chapter, it is finished here.

The phases of Mitosis will be discussed in next chapter
You can see CELL CYCLE and MITOSIS in the U-Tube below-
U-tube link

[ ইংরেজীতে প্রকাশিত করা হল কিছু কিছু বাংলাদেশী বংশোদ্ভূত বিদেশে অবস্থানরত ছাত্র পাঠকেরা যারা বাংলা ভাষা পড়তে পারেনা, তাদের অনুরোধে,দুখিতঃ]

Let us now enter inside a cell factory and see how the cell synthesizes Trillions of new cells through Mitosis process. You must surprise to see such strange activities of cell-factory.

Mitosis process has been divided into 5 stages as-


(The 1 st stage of Mitosis)

At normal condition, the Chromosome remains loosely packed and non-visible in the Nucleus of cell. After DNA replication at S phase of Interphase, Chromosome begins condensing. At this time the Sister Chromatids accept stain and become visible under Electric Microscope. At this position, they are called Chromatin.

Chromatin is called a complex of macromolecules found in cells, that consist of of DNA, protein and RNA. The primary functions of Chromatin are as:-

1) To package DNA into a smaller volume to fit in the cell,

2) To reinforce the DNA macromolecule to allow Mitosis,

4) To control Gene Expression (See chapter11).

5) DNA replication (see chapter 4).

The primary protein components of chromatin are Histones that compact the DNA. (2)

Chromatin packs DNA as winding like thread, keeping the protein Histone at core center.

The pair of sister Chromatids are attached in together at the Kinetochore of Centromere with a protein called Cohesin.(3)Figure-2

One Centrosome remains beside a Nucleus that divides into 2 while Mitosis begins and separates away.(1,13).

Centrosome is composed of 2 Centrioles (6). Centrosome, by controlling microtubules, detaches the 2 Chromatids and takes them at 2 corners of cell.

Microtubules, a dynamic 25 Micrometer-long, made-up of Tubulin- protein , are a part of Cytoskeleton which is a Cytoplasmic component of cell (7) Figure-2.

Nucleolus remains as a non-membrane- bound body inside the Nucleus. Inside Nucleolus, there remain Nucleic acid and protein. The function of Nucleolus is to transcribe Ribosomal RNA (rRNA)(8),Figure-3.

At this stage Nucleolus disappears and does not need division. At later stage, it re-appears and goes in new cells. (1)

Figure-5, kinetochore`
Green color- Microtubule, Blue color- Chromosome, Pink color-kinetochore.

Prometaphase is partly the end of Prophase and partly the beginning of Metaphase. At the beginning of Prometaphase , phosphorylation of Nuclear Lamins (14) causes the nuclear envelope to disintegrate creating pores upon it.

Then Centrosome sends Microtubules through these pores inside the Nucleus.

There are 2 Kinetochores for 2 Chromatids at each Centromere. Figure-5, (9).
Kinetochore is a ring shaped complex protein compound. Microtubules, just like a Fishhook, have a hook at its forward end. Microtubules come from both sides of the Centrosome to the Kinetochores of the both Centromere of both Chromatids and catch the Centromere by introducing its hook into the ring of the Kinetochore, just as we catch fish with Fishhook.

By this way, both the Chromatids are captured by the Microtubules coming from their own side of Centrosome.
If the Microtubules, coming from both sides of Centrosomes, cannot get any Kinetochore join together forming spindle. (1)

On the next step, just like catching fish with Fishhook, the Microtubules start pulling the Chromatids, separate them from one another and drag them towards their own corner of Centrosome.
Here, power is supplied by ATP. There are still many facts remaining mysterious to the scientists about the Kinetochore.
( The 3 rd stage of Mitosis)

Figure-6, Metaphase.
The Greek word “META” ( μετα) means “AFTER”.
Metaphase starts after introducing the hook of Microtubules into the ring of Kinetochore. Figure-6, (1)

At this phase, chromosomes come on a line remaining at an equal distance from the both corners of Centrosomes that is called Equatorial line or Metaphase plate. Figure-6, (1).

At this phase. the Centrosomes of the both corner drag the Chromatids linearly towards their own corner through their Microtubules. What happens here is just like a tug-of war in between 2 opponent powers. For this tug-of-war like pulling and dragging in between 2 opponent forces, upon the Chromatids, there remain chances of some accidents like tearing or breaking of chromosomes, that occur some times also.

Sometimes we have to suffer also for these bad incidents.

Such errors are called “Chromosomal Aberration” that will be discussed a little at the end of this chapter.
For proper Mitosis, it is very essential that each Kinetochore should receive one microtubule. If incidentally, any Kinetochore misses a Microtubule, the kinetochore sends a signal to Mitosis process not to ahead further towards the next Anaphase stage.

This kind of warning- message is called “Mitotic Spindle Checkpoint” (10)

It can be compared with such an incident suppose an aircraft is going to start carrying 200 passengers from Shahjalal airport of Dhaka to JFK airport of New York. After a while the pilot started the plane in scheduled time. But still, one passenger remained outside the plane.

Then that passenger sent a message to the pilot to stop and carry him with. In response, the pilot stopped the plane and ensured his access into plane, and then he restarted.

During mitosis so much care is taken. Instead of so much care, still there happen some errors.

If there would not remain such fine coordinated work process in our body cells, the cells would grow sick cells and at the same time we also become sick and our life would fall in danger.

( The 4 th stage of Mitosis)

Figure-7. Anaphase
Anaphase ( Greek word ανα means “up,” “against,” “back,” or “re-”).

Anaphase stage starts when all the Kinetochore receives Microtubules and all the Chromosomes come on the Equatorial line in a row.

1 ) The protein (Cohesin) which attached the Chromatid pair at the point of Centromere is cleared off.

2 ) Each separated chromatid now convert into new Chromosomes and are dragged to Centrosome situated at the 2 corner of Nucleus, with Microtubules. Figure-7

It is to remember, that each separated chromatid in both sides has now formed a new Chromosome that contains the Homologous Chromosome of father and mother also.

The Microtubules drag by shortening. It is still mysterious to the scientists that why and how the Microtubules shorten and drag.

While the new chromosome move towards Centrosome, centromere remains at forward end followed by Chromatid, like a “V” shaped sign, and it seems that one chromatid wants to grab other. (1)
( The 5 th stage of Mitosis)

Telophase ( a Greek word “τελος” means “end”) is reverse to Prophase that is, Mitosis starts at Prophase and ends at Telophase. Figure-8

Microtubules and kinetochores gradually become thinner and disappearing as the new Chromosomes arrive at the corners. At this phase the cell elongates with the elongation of Microtubules, and the nuclear envelope and nucleolus that disappeared at the 1 st phase, now re-appear, keeping the new Chromosome inside the Nuclear envelope.

The Chromosomes, at this phase, again become thinner and loosely packed as before.

Up to this, the Mitosis process is completed, but cell division yet not completed. Cell division completes after Cytokinesis process. (1)

Muscle cell don’t go under cell cycle. (Video-2)

Cytokinesis starts at Telophase stage, although it is not a part of Mitosis. Mitosis and Cytokinesis ,in together, are called “MITOSIS M PHASE” In this phase, a groove appears at the Metaphase Plate Level on cell wall. Then 2 collapsible rings appear here, the cell divides into 2 cells and the 2 new cells along with their new chromosomes separate away. Finally, at this stage the parent cell has already produced 2 clear new cells. (1) figure-9.

By this way the 100 trillion of cells in our body are produced and, in fact, our body is a product of this cell- factory.

How marvelously is operated the functions of this cell factory.

Just same as the world famous “General Motors Co.” might make some errors while producing their machinery parts of their cars, cells also could likely make errors while they divide to produce new cells. This is called “Chromosomal Aberration”.

In fact, “Chromosomal Aberration” occurs rare in Mitosis. Most “Chromosomal Aberration” occurs at Anaphase stage when the microtubules start dragging and pulling upon the Chromatids to separate from one another to carry them to their poles.

There remains most chance of occurring Chromosomal Aberration in Mitosis during the embryonic stage of baby (1). Chromosomal Aberration in sex cells may produce baby with varieties of hereditary diseases or abnormality.

There are 2 types of Chromosomal Aberrations-

1) Change in number of Chromosomes in cells- It occurs for non- disjunction or failing to separate the Chromatid pair.

For this, sometimes 3 Chromosomes may go to one cell that is called “Trisomy”.

And another cell may receive one Chromosome that is called “Monosomy”. If this cell lives may grow as a cancer cell. This type of Aberration is called “Aneuploidy” or abnormal Chromosome number.
2) Structural change- That is change in the structure of Chromosome.

Structural change may occur in different forms as-

  1. a) Deletion- that is missing any part of Chromosome.
  2. b) Insertion- that is any part of chromosome placed not fit for it.
  3. c) Inversion- it occurs when the ends of Chromosome placed reversely.
  4. d) Translocation- it occurs when the place of one part is changed with another part.
  5. e) Duplication – it means when a part is placed double .
  6. f) Ring formation- it occurs when a part of Chromosome tears and hang as a ring.
  7. g) Chromosomal Instability- when it happens, the Chromosome cannot work properly with stability. (11, 12)

The references of Chapter-7

Chapter 8, The Cell Division “Meiosis”- Never One Person Can be Exactly Similar To Another Person In World (Except Homozygote Twin)

[ ইংরেজীতে প্রকাশিত করা হল কিছু কিছু বাংলাদেশী বংশোদ্ভূত বিদেশে অবস্থানরত ছাত্র পাঠকেরা যারা বাংলা ভাষা পড়তে পারেনা, তাদের অনুরোধে,দুখিতঃ]

The sex cells, the spermatozoa and ovum, divide in Meiosis process in testis and ovary respectively. Before division, it contains 23 pairs or 46 chromosomes that are called diploid, and after division only 23 that are called haploid.

In other words, each sex cell after division owns half number of chromosomes’

After sex, this haploid sperm fertilizes haploid ovum at the Fallopian Tube of Uterus producing a diploid cell called Zygote. This Zygote is the beginning of our life. And this one-celled-Zygote grows up as a person like us through Mitotic Division.

Now I want to take you into the stranger type of cell activity, the Meiotic Division that must surprise you.

In fact, through this complex process, not only our life starts but our fortune also selects.

So, who is there that would not be interested to know how he could visit this world?

But none of us could reach this beautiful world through a clean and safe way. To reach here, we have to pass a very terrible dangerous way.

Let us now enter into the cell-factory to see the Meiosis process.

But before entering, you have to know at least some thing about chromosome, since chromosome is the main subject matter of this factory.

Why is the importance of Meiosis so much upon the animal world?

Through the Meiosis, the genetic quality not only enters into the grown person, but also transmits to our descendants. In Meiosis, decision goes to confirm what type of genetic qualities is going to enter to the person grown with that particular sex cell. Here the genetic qualities go on sorting among 70 trillion varieties of genetic option.

Yes, it is really a dangerous matter!

Through the processing of this factory, it goes on selection that the person will be produced is either an Einstein, psychotic, insane, destroyer of human civilization or a Down’s syndrome like patient. Not only life is created through this Meiotic factory but the varieties of living world are also expressed through the variation of genetic materials, and also by this way the evolutionary changes occur in animal kingdom slowly. (2) See video-1

It is a strange matter that we ourselfs are sufferer of all products of this factory but we know nothing about it. Still this is an unknown world to us. It seems that we are being controlled with an expert unseen hand in this world. Here we seem to be not more than an idol-machine.

Then who is the controller of this idol-machine?

Yes, Thus far we know there is a controller and it is the DNA.

How long will be moving this idol- machine? The straight answer is “as long as the power will persist in its battery”. Then what is the battery of DNA?

Yes, certainly DNA has battery. It is the “Telomere’. So when the length of “Telomere” reduces, the dial hand of our life clock also reduces, just like, as the battery power of a torch reduces, the torch also reduces its sharpness of light. When the battery power of our DNA reduces, our cells gradually go on natural death heading us towards oldness and gradually to our natural death.

(What is Telomere? See chapter-5)

Suppose, after 10-20 years, the scientists would have discovered, how the DNA battery could be recharged, we would be great fortunate to gain a long-young-life!!

Really we are helpless. Do we have any capacity to protect ourselves if an aberrated or any of thousands types of sick genes like Down’s Syndrome, Thalassaemia or Cancer etc. enter into our chromosome during the genetic exchange in Meiotic division of our parent sex cells?

Yes, a person may be a victim of thousands types of congenital abnormalities or diseases due to an erroneous mixture occurring in Meiotic Division.

About genetic aberration has been discussed a little at the end of this chapter.

We have no control over that strange factory! We are very helpless over there. Yes, you can understand clearly how we are coming through this strange factory if you go through this Meiosis chapter carefully.
Before that, it is better to know a little about the organization that has enlightened the world with the knowledge upon DNA by researching and discovering new things. We should have at least a little gratefulness to them.

What is Human Genome Project?

Human Genome Project Is an international research project whose research target is to identify the whole human gene and the gene sequences. The project was initially created by the co-ordination of The U.S. National Institutes of Health and the U.S. Department of Energy’. And later many universities of U.S. U.K., France, Germany, Japan and China added more contributions on it. “Human Genome Project”, in fact started working in 1990 and finished its work in 2003, 2 years earlier than the scheduled time.
These researchers had been able to identify the blueprint (gene) of human hidden in DNA. And it contributed many types of advantages related to medical, social and legal matter. (6)

To understand Meiosis, it is necessary to gain little idea about chromosome beforehand. Later it would be described elaborately.

So, to have a little idea, at first you can see the map of all chromosomes that is called “Karyotype”. Since in Meiosis the division of these chromosomes is the main subject, so know about them a little beforehand, and also know their structure going through chapter 1 and 2.

We have to know that there are 23 pairs or 46 chromosomes in our all somatic cells (and sex cells before meiotic division). Somatic cells are all the body cells except sex cells. The scientists have set all the 23 pairs of chromosomes in the form of a map called “Karyotype” that helps compare the abnormal or diseased chromosome with the normal and healthy chromosome during test. (Figure-1) .There are 2 sets of chromosomes in all 23 chromosomes, inside the nucleus.

One of these comes from mother and other from father. The number of sets is expressed by “N”. In all somatic cells contain 2 sets in each chromosome, so it is expressed as “2N”. In scientific language it is called “Diploid”. “DI” means 2. Then in 23 chromosomes contain 23ࡨ=46 sets. And in male and female sex cells remain 2 sets (Diploid) before Meiotic division, and I set after Meiotic division that is expressed in scientific language as “N” or “haploid”. So in sex cells after division remain 23ࡧ=23 sets or 46/2=23, that is half number of set and called it ‘haploid”.

There are thousands of genes in chromosomes which not only run our body but also transmit the genetic qualities from our parent to us as well as from us to our descendants.

As we already know, our life starts with a Diploid cell, the “Zygote”, produced by the fertilization of a haploid female sex cell, ovum, with a male haploid sex cell, sperm.

In the Meiosis process it has been explained how a Diploid sex cell converts into a haploid sex cell. The Meiotic division is a very complex process.

Figure-1, Karyotype – In the form of map, 23 pairs of chromosome in all the somatic cells (and in sex cell before division)

In this figure, the first 22 pairs of chromosome are called Autosome, and the last 23 rd pair (X and Y) located on the lowest right corner, are sex determining chromosome, so it is called Sex Chromosome. And one set of these 23 pairs is called Homologous for other. It is called homologous because, they are equal in size and shape and their Centromeres remain at the same level. But they are not identical set as become in Sister Chromatids. They are numbered serially from longer to shorter as 1,2,3,…….23.

So, the chromosome number 1 is the longest one. (1) Figure-1.

To guess the Karyotype of a sperm or ovum after division, imagine one set of chromosome in place of two sets in all 23 chromosomes in the above Karyotype map.

Because, in the sex cells after Meiotic division remain 1 number of set or N (haploid) in place of 2 number of sets or 2N (Diploid).

SEX CHROMOSOME (The sex determining chromosome)

From parent chromosomes, during fertilization, when meet X and y chromosome, produce male and when meet X and X chromosome produce female baby.

So in all somatic cells and undivided sex cells of a male contains XY set in 23 rd chromosome and in female contains XX set.

For example, in the above figure, the 23 rd chromosome contains XY set, so you can easily say this Karyotype is taken from a male body cell.

You can also easily say that there is no Trisomy or Monosomy in this Karyotype, since all chromosomes contain 2 sets not 3 or 1 set in any one.

The male Diploid sex cell, after Meiotic division, produces 4 haploid sperms of which some contain X set and some contain Y set in 23 rd chromosome.

And the female diploid sex cell, after meiotic division produces a haploid ovum cell containing 1 X set in 23 rd chromosome, and 4 polar bodies. The polar bodies remaining along with the ovum protects it, and later inactivated. It is not produced uselessly. (1, 3, 7)

Cell Cycle and Meiosis
Like Mitosis, Meiosis has no cell cycle. It is a one-way-process. (2) Figure-2

Figure-2, Meiosis and Cell Cycle.

There are some differences between Meiosis and Mitosis, as-

1) Mitosis occurs in all somatic cells, where Meiosis occurs only in sex cells.

2) Mitosis has a cell cycle, where Meiosis has no cell cycle. It is a one-way-process.

3) Mitosis completes within 5 stages and new cell re-enters the cell cycle (See Chapter-7), whereas Meiosis has 2 stages 1) Meiosis -1, 2) Meiosis-2.

Then the both stages have 5 phages, as 1) Prophase-1, 1) Metaphase-1, 3) Anaphase-1, 4) Telophase-1, 5) Cytokinesis-1.

4) In Mitosis, a cell divides into 2 new cells, and the divided new cells contain the same number and exactly the same quality of parent chromosome set. That is, the parent cell is a Diploid (2n) cell containing 2 sets of chromosome and the divided new cells have also 2 sets of chromosome or Diploid (2n), and the genetic qualities are also exactly same without any change. .

In Meiosis, a sex cell divides into 4 sperm cells in male and 1 ovum in female. Here the parent cell is a Diploid (2N) cell, containing 2 sets of chromosome and the sperm or ovum is a haploid (N) cell, containing only 1 set of chromosome, not any pair. Here the parent cell- chromosome and the new cell-chromosome are different in genetic qualities, and the new cells are also different from one another in genetic qualities. (2)

A limited number of ova are produced in ovary before birth in female. No new ovum grows after that (3).

But billions of sperms are being produced from puberty to death continuously in male (4).

Now let us see how a Diploid sex cell forms a Haploid reproductive cell after passing through the phases of Meiosis one after another.

Meiosis has been divided into 2,

Before starting Meiosis, some process is completed in interphase that is necessary to describe.

Like Mitosis, in synthesis (see chapter-7) phase, each of 23 chromosomes becomes double by Replication (figure-1). That is, a father and a mother homologue of a chromosome form 4 chromatids. One chromatid of a pair is called the sister chromatid of other one.

Chromatid is called the “set” of chromosome produced after Replication. As a diploid chromosome after replication produces 4 sets, So, they are called 4 chromatids.

What is the “sister Chromatid”?

‘Sister Chromatids” are the Chromatids of the same Homologue.

What is “non- sister- Chromatid”?

“Non- sister chromatid” is the chromatid of different Homologue. In other words, a Chromatid of one homologue is a non- sister -chromatid of the other Homologue’s Chromatid.

One set of a pair in a chromosome is ‘homologue’ to the other set of the same chromosome, of which one homologue comes from father and other from mother.

The 2 sister chromatids are joined together like ‘X “at Centromere. (2) [Figure-2 and see video 1, 2 and 3]. The sister chromatids remain identical or having exact quality until they cross over.

The genetic qualities of Non-sister-chromatids are different.

What happens in Meiosis-1?
Functions of Meiosis1

1) To mix haphazardly the genetic materials of father and mother chromosomes through Crossover and Recombination. After mixing, the genetic qualities in all the 4 chromatids of parent chromosomes change and each of them differs from other carrying each one a different type of genetic quality (2).

2) The Diploid chromosome of parents transform into Haploid chromosome. (2)
There are 5 phases in Meiosis-1

They are- 1) Prophase-1. 2) Metaphase-1, 3) Anaphase-1, 4) Telophase-1, 5) Cytokinesis-1.

In Meiosis-1, the cell divides into 2. And in each cell, enters a copy of Homologous chromosome that was replicated in synthesis phase of interphase. This cell is called haploid, although it has 23 pairs of chromosomes, because, here, unlike in Mitotic division, each chromatid carries a different type of genetic quality from other. (2), Figure-2, See the videos.

In Meiosis-2, the 2 cells produced in Meiosis-1, just like Mitosis process, divides into 4 haploid cells, each containing a different quality of chromatid (called it now Chromosome) through the phases, Prophase-2,Metaphase-2,Anaphase-2, Telophase-2 and Cytokinesis-2.(2)[ Figure-2, see the videos]

Meiosis is complete. But this is the Prophase-1 stage where the transformation of Diploid to haploid and exchange of genetic materials among the chromatids occur.

For this reason, Prophase-1 is the longest and most important phase, where all the complex functions are performed.
Now see the phases of Meiosis.

The main function of this phase is to transform the Diploid Homologous parent chromosome into haploid chromosome through mixing their genetic materials.

It has been described here how this complex function is performed through Crossover and genetic Recombination.

To understand Crossover and Recombination clearly, see the figure-4, below-


To understand the figure easily a description is given below-

1) There are 2 columns in the figure, “A” on left and “B” on right. Say, the blue colored chromosome is for father and red one for mother. “A” column is marked with “NO CROSSING OVER” that means in this column no Crossing over or genetic Recombination happened. So, no genetic exchange happened among the parent homologous chromosomes in this column. For this, there is no change of color in the 4 chromatids in the lowest line. Such occurs in Mitotic division and also in Meiotic 2 division.

2) Now look at the right “B” column. Here one non sister chromatid has crossed over another non sister chromatid exchanging their genetic material mutually, represented by color change.

Look at the top figure, one non sister chromatid has touched the other non-sister chromatid crossing over it. This touching point is called Chiasma.

Through the touching point they exchange their genetic materials in between them.

Look at the middle figure, a portion of mother’s chromatid (red) has changed into blue color exchanging with fathers genetic (blue) materials.

On the same way, also the corresponding portion of father’s chromatid has changed into red color exchanging with mother’s genetic materials. Here, exchange of color represents exchange of genetic materials.

So, in this way, the chromatids of parent chromosomes re build their genetic qualities by mutual genetic exchanges through cross over. This re-building of genetic qualities is called Re-Combination.

It seems they are very expert to complete such complex function. With so expertise, yet some error or aberration occur for which the victim has to suffer some times.

Look, as there occurred no cross over in between the other 2 chromatids, there is no exchange of genetic materials and also no color change.

To understand clearly, the 4 chromatids are shown separately in lowest line.

By this way, the parent sex cells mix thoroughly the genetic materials of their chromosomes through Meiotic division, in Prophase 1 phase while producing Gametes (sperm or ovum). They follow no certain rules or regulations for this exchange, and yet, it is totally beyond our control.

Later through sex, when this sperm meets ovum in uterus and fertilizes, then our life starts as a single cell called “Zygote”.

The main significance of meiosis process of sex cells remains in Prophase 1 stage.

The main controlling key of our fortune is produced in this phase and our luck also built here.

. This genetic mixture in chromosome happens only at the early first stage of Meiosis Prophase- 1.

No genetic exchange occurs further in other phases. Here is an interesting matter they do not follow any hard and fast rule in regard which chromatid or gene will participate in exchanging genetic materials with which chromatid or gene. They are totally independent to choose this option. This is called “Independent Assortment”.

Do you know what does it mean?

It means, It produces sperm and ovum through randomly mixing the genetic materials according to its (the process) choice and stores as a raw material in testes in male and in ovary in female. Later, human grows according to the quality of the particular sex cells that participate in fertilization in uterus through sex. And then the product is expressed as human like us in this world market. We may assume this random genetic mixture occurs haphazardly, but it may not be haphazard mixtures to the process. To it, this may be a definite pre-planned matter with a definite target, since evolutionary process in animal kingdom advance through this pathway.

In this way, when it (the process) wishes can grow a person like A.P.J, Abul Kalam the BHARAT RATNA from a lower family of Tamil Naru (11).

This is why I am saying “this mixture may be haphazard to us but not to the process”.

Look above the figure-5, Prophase 1. Every process in this phase goes on like Mitotic process (part-7), except some especial process.

First Homologous chromosomes of father and mother are replicated. Then they exchange their genetic materials mutually through Crossover mechanism that discussed above.

Do you know what the result of it is?

As a result of this randomly genetic mixture in 23 chromosomes of sex cells, there is chance of production of a sperm or ovum having any of 70 Trillion varieties of different genetic qualities.

It means, when you grow you are unique in this world, because, the genetic qualities you received, are sorted from 70 Trillion varieties of different genetic qualities. In other way, there was chance of growing any other one sorted from 70 trillion of other different unique variety of genetic qualities, in place of you, with the same parent sex cell, through random selection during cross over. (See video-2)

It means any one growing in this world he/she comes with a pre-selected unique quality and fortune.

We have no control over there yet. So, we cannot grow, according to our wish, a very talent person as well as we cannot also prevent growing of a dull, Insane or diseased person.

So, it is quite impossible to grow a person exactly similar to another in this world, except ‘Homozygote twin”.

Why Homozygote twin become exactly similar?

The zygote starts dividing mitotically keeping the chromosome in the daughter cells exactly similar to parent chromosome. If any of these daughter cell starts growing separately, it forms a Homozygote (Monozygote) twin having the exactly same quality, since the chromosome of daughter cell and parent zygote cell are exactly same.(8)

Scientists are producing animals artificially using this formula called “Cloning”

The FDA of U.S.A. has approved marketing this meat without labelling, on December 28, 2006 (9).

(What is cloning? See chapter-(15)

The further process happens just like Mitosis (See chapter-7)

The main target of Meiosis, which qualities will have the person, is germinated in this Prophase 1 phase. But to reach final, it has to pass other many stages with safely.

The functions of next phases are only to transform the sex cell as sperm and ovum and to store them as raw materials for production, in Testis of male and in ovary of female respectively. Later, they meeting together during sex, produce Zygote in uterus, grow gradually carrying the exact qualities prescribed in them and express as final product human with the prescribed qualities, over the world market.

But, scientists have now discovered technique to grow baby without sex fertilizing the ovum outside body which is called IVF or In-Vitro Fertilization. (Go through chapter 19 to see the IVF elaborately). We call it “Test-Tube Baby”.

Question- Can we bring any influence or control over the production of these raw materials, the sperm and the ovum, so that we can choose to produce a baby with good genetic qualities or avoid the bad genetic qualities or diseases, according to our choice?

Answer- May be, but the scientists have to research enough to reach there. It is an object of too far.

Say, it is yet many times farther to scientists than the farther way to travel from our earth to reach the Exoplanet Kepler-452b (10)

But, I believe, human should not gain this power.

Because, then human would create such a Hitler who could destroy the whole world, competing in fighting one group with their opponent group.

In this phase, The Microtubules bring the Homologous pair in a row on the Metaphase Plate or Equatorial line, connecting to the Kinetochore of Centromere. It does not obey any rule that which Homologue will choose the witch side. This is called ‘Independent Assortment” (Already mentioned before). They choose the side according to their wish and plan.

Each of these 2 Homologue chromosomes is going to their poles to produce 2 different cells in Mitosis 1. Here, another type of sorting process occurs. Suppose, a Chromatid of one side contains Cancer gene and others are good. Thereafter, if anyone grows with the sex cell produced by the Chromatid containing Cancer gene will suffer from Cancer disease and if any one grows by the other cells will not. (See Video-1)

Nucleus envelope disappears in this phase. (2) Figure -6.
3) Anaphase-1

In this phase, the Microtubules, by shortening itself, pull the Homologous Chromosomes towards opposite direction to their own Centromeres. The microtubules, which do not get any Kinetochore, form spindle and being longer itself, elongate the cell. You are to keep in mind that These 2 Homologous Chromosomes contain 4 Chromatids each already carrying different types of genetic materials. (2) Figure-7.
4) Telophase-1

In this phase, the Chromosome pair reaches at 2 corner of cell. The Nucleus envelope reappears and encloses the new chromosome, keeping the Centrosome outside the envelope. A furrow appears on cytoplasm at the middle. Each Homologue contains a pair of Chromatid. (2) Figure-8
5) After this, 2 separate cells are produced through Cytokinesis-1(2) Figure-9.

Meiosis-1 finished. Look, in Meiosis 1, one cell divides into 2, each containing a Homologous Chromosome, having different type of genetic quality. Then cell goes on rest entering into Interphase 2. DNA does not replicate in Interphase 2.

Now the cell will enter into Meiosis 2.

In Meiosis 2, these 2 cells will split into 4 cells, each having 1 Chromatid just like Mitotic division, but carrying with different genetic materials.

Now see the Meiosis-2. Its phases are: – 1) Prophase-2, 2) Metaphase-2, 3) Anaphase-2, 4) Telophase-2, 5) Cytokinesis-2.

Here everything happens just like Mitotic process except, the Homologous have already transformed into haploid and the Chromatids have different varieties of genetic material, acquired from Meiosis 1. Chromosomes start condensing. Sister Chromatids are attached at centromere in Kinetochore.

The Nucleus envelope disintegrates creating holes allowing Microtubules entering inside. The Microtubules connect the Kinetochore. The Microtubules, which do not get Kinetochore form spindle. (2)

Here also like Mitotic process, Chromosomes come in a row along the Metaphase plate. Something difference from meiosis 1 here Metaphase plate turn 9o degree around, so that the Chromatids going to form new Chromosome soon, can separate freely and go to their own new cell, figure-11 (2).

Like Meiosis 1, here also another sorting or “Independent Assortment” occurs, that means the Chromatids freely choose their sides where it wants to go. This is the final sorting stage. So, if a person grows with the sex cell containing the Chromatid having Cancer producing gene, the person will suffer from Cancer.

At this phase, the Microtubules separate the Chromatids from Centromere and pull towards there pole. This Chromatids are called sister chromosome because they are the future-chromosome of new cell. (2) Figure- 12
4)Telophase 2.
Figure source-

Figure-13, Telophase-2.
In this phase, like Telophase 1, the spindle fibers disappear and nucleolus that disappeared in 2nd phase, re-appears. Each cell contains a haploid chromosome. Furrow appears in the middle. (2) Figure 13

Now, through cytokinesis 2, a male sex cell produces 4 sperm cells each having a haploid chromosome of different types of genetic qualities and a female sex cell produces one ovum having haploid chromosome and 3 polar bodies that are inactivated later (Already told before)
Meiosis is complete. Figure-14 (2)

During meiosis a lot of Chromosomal Aberration may occur. Some are described here.

Some errors in Meiosis (Non Disjunction)

If a Chromosome or Chromatid cannot separate correctly in the Anaphase stage of Meiosis 1 or Meiosis 2, is called “Non Disjunction”. As a result, on cell may receive 3 Chromosomes that is called “Trisomy” and another cell may receive 1 Chromosome that is called “Monosomy”.

For this, many types of congenital diseases are seen in medical field.
1) PATAU SYNDROME – It happens when Trisomy occurs in Chromosome number 13.

They grow with many types of symptoms like, mental prematurity, motor neuron disease, microcephaly, joined fingers, bifurcated lip, etc.

2) EDWARD’S SYNDROME- It happens when Trisomy occurs in Chromosome number 18.

Its symptoms are atrial septal defect, ventricular septal defect, patent ductus arteriosus, premature mental condition, slow growth, arthrogryposis (congenital joint stiffness) and more.

3) DOWN’S SYNDROME- It happens when Trisomy occurs in Chromosome number 21 The symptoms of this disease are as, abnormality in neurological system, congenital heart disease, abnormal Thyroid gland, Cancer, sterility. Audio visibility problem and more.

4) KLINEFELTER’S SYNDROME- It happens when Trisomy occurs in Chromosome number 23 in male, like XXY.

When it happens, the victim has less capacity to learn language or anything or to run an action where fine multiple coordinated works required.

5) TURNER’S SYNDROME- it happens in female when she receives one x chromosome like, X0.

They have symptoms like sterility, abnormal face, bicuspid aortic valve, coarctation of aorta and more.

6) TRIPLE X SYNDROM- It happens in female when she receives three X chromosomes like, XXX. It is a Trisomy.

They have a long body size with small head. Also some may not have any symptom.

7) XYY SYNDROME- It happens in male when Trisomy occurs with Y chromosome.
No symptoms appear in this error. In London, this type of error has been identified when person’s Karyotype is tested. Beside these, there are many types of chromosomal aberrations that we would know later.

Keep in touch to know about the mystery of human body.

See the videos upon Meiosis below-

Chapter-9, Chromosome, The Blue Print of life, Where our Parents.

[ ইংরেজীতে প্রকাশিত করা হল কিছু কিছু বাংলাদেশী বংশোদ্ভূত বিদেশে অবস্থানরত ছাত্র পাঠকেরা যারা বাংলা ভাষা পড়তে পারেনা, তাদের অনুরোধে,দুখিতঃ]

American geneticist & physician, Walter Sutton (Left)
(April 5,1887 – November 10, 1916) and German Biologist, Theodor Heinrich Boveri (Right) (October 12 1862 – October 15,1915) advanced the Chromosome theory in 1902.(1)

DNA and Chromosome is same thing. The difference is that the DNA is a long thread like structure remaining unpacked condition, and Chromosome is called when this long DNA thread is coiled many times and packed and compressed tightly keeping the protein, Histone, in central core.

Suppose, some Shrimp producing business man of Bagerhat, Bangladesh wants to export Shrimps to New York. If he exports it unpacked and unprotected it will rot and be damaged and will be unusable for New Yorkers to eat it, when it will arrive there. So the Shrimps must be packed and protected well.

This is why the DNA is packed tightly and well protected as Chromosome to keep it safely, that transmits the Blue Print of our life from generations to generations forever.

Also some other proteins as Nucleosome and Chromatin help in this packaging.

The tightening and compacting has been performed with so much expertise technique that a 6- feet- long DNA can hold inside a micro nucleus and the DNA can also work freely by uncoiling and unpacking during Replication and Transcription(see chapter-3) with safely.

During such innumerous kinds of activities, DNA has once to uncoil and open, and after finishing the work it has once to re-coil and re-pack safely, just as you open and elongate your measuring tape during work and again coil it in a small box when your work finished.

Never, this Blue Print of life, the DNA, asks any suggestion or even any little price for its complex works to us or we pay for it. Cell itself is continuously running this work always with high intelligence finely and appropriately beyond our knowledge.

We are very fortunate that about 20,000-25,000 Genes are providing very important services for us for 24 hours sleeplessly all over the life freely.

If we had to pay them even a little, our condition would be worst. Such as even when we are attacked with Diarrhea or Typhoid we find it hard to bear the treatment cost.(1,2)See the video-1, and figure-2.
Figure source-

Little description of the figure-

It is to remember that Chromosome is not visible under microscope at normal condition. It is only visible when Chromosome replicates and the Chromatin particle condenses accepting stain during cell division.

So, this figure is the photo of the replicated chromosome, before cell division. Look, there is double helix of DNA at right and above. It has formed as chromosome by coiling and packing keeping the protein, Histone, at central core. Each of these strands is called Chromatid and one of these is a sister Chromatid to other. The genetic materials of sister chromatids are identical (see chapter-8 for details)

There is a little constriction at a position little away from the middle on the body of each that is called “Centromere”. At this point the body of one Chromatid is attached with the other one, so that they cannot separate. Why? Since, if they septate earlier, cell division will go in wrong way. The aim of cell division will fail. During cell division both of them should go towards opposite side. If they go towards same pole, a genetically erratic cell will produce that is very dangerous.

So, they separate exactly at the correct time at the Anaphase stage of the cell division when they have to go towards their opposite pole. They have to perform each of their activities correctly. If, anyway, they make even a little error, we have to pay a high price for that. (See chapter-8)

The paired sister Chromatid is seen as “X” with 4 arms. For the specific location of genes, the scientists have given different names of the arms of 2 sides of this centromere. The short arm is named as “p” arm and the long arm as “q” arm.(2), Figure-2, (see also videos)

In human, 23 pairs or 46 Chromosomes remain in Autosome cells and 23 in sex cells after division. Almost all genes remain in these Chromosomes. These chromosomes remain in nucleus. So the nucleus is the control center or capital of cell.

Besides, there are some Chromosomes in mitochondria, a small organelle, in Cytoplasm, most of which come from mother. Most of father’s mitochondrial chromosome remains at the tail of sperm to supply energy while they advance swimming. And the tail remains outside while fertilizing ovum

This is why the baby receives more DNA from mother than father. The mitochondrial DNA does not remain packed rather it remains as thread. Bacterial DNA is also like thread not packed.

For this scientists believe, at early time human cell would have been infected by some bacteria. So this is the sign for that.

The total DNA including 23 pairs in nucleus and some in Mitochondria is called “Human Genome”. Since chromosome remains inside the nucleus, and Red Blood Cell (RBC) does not have Nucleus, so the RBC also does not have any chromosome

The Genetic Book of our life.

Is it surprise that our life is governed exactly as inscribed in our genetic book? In fact, our body can do nothing beyond the inscription written in our genetic book.

It is just like as the capacity of manager of the Nissan Motor Company is limited in producing car within the formula prescribed by the owner of the company. All the performance of his industry is bound in his formula. The manager has no capacity to do beyond this formula.

Yes, really, 2 big copies of book in each of 100 trillion cells, containing all the instructions of our life, are saved since the early one-celled Zygote up to our death. Do you know who of our closest relative have offered this invaluable book to us? Possibly you do not know it. Listen now we received these 2 invaluable books from our nearest relatives, one from our father and other from our mother, just like, as you can imagine, they offer their properties to us freely.

So, we don’t have any way to deny or be thankless to their contributions. Each of our 100 trillion of cells is always admitting the memory and presence of our parents in them.

So, you have also to do likewise. I am not expressing here the verses of any saint rather expressing that is found acceptable scientifically.(2,5)

In each volume of the book, there are 23 chapters of different types and sizes. The 23 Chromosomes of parents represent 23 chapters. The each page of each chapter of these books is filled with the genetic codes that contain the instructions for governing our body.
The number of genetic codes varies from chapter to chapter. For example, the Chromosome number 1 contains 4220 genes, the highest number, and chromosome number 11 contains only 379 genes, the lowest number. And if any new gene discovered, the number will also increase. (1,2)

Scientists have already discovered that to write the genetic instruction in all over pages of these books, cell has used only 4 chemical-code-letters that are A,T(or U),C,G. And a word is made with any of these three chemical letters. Each 3 letters (triplet) is called a “Codon”. (What is Codon? See chapter,3), (See figure 3,5)

These 4 chemical words represent 4 chemical compounds, Nucleotides (Already mentioned earlier) as, A=ADENINIE NUCLEOTIDE, T= THYMINE NEUCLEOTIDE, C=CYTOSINE NUCLEOTIDE G=GUANINE NUCLEOTIDE.U=URACIL NUCLEOTIDE (See chapter 2))

Our body cell reads the message written with the chemical codes sent by DNA, just like as we read words on a page. Then cells follow the instruction of DNA.

There are innumerous types of works, cells have to do. Different kinds of cells have to perform different kinds of works. For example, Heart cells have to a type of work Liver cells have to do another type of work and so more.

So, they have to perform different kinds of work in different places.

DNA sends specified instruction to the specified cells as they need.

You can imagine it just as the central administrative office of a state sends different kinds of instructions to its different kinds of administrative branch offices to coordinate proper administration, as it sends a type of instruction to the Law enforcing branch, another type of instruction to the Medical branch, another type of instruction to the Education branch, and so on.

If it sends one’s instruction to other, the state will not run. So, they will never do it

On the similar way, DNA also sends the specified instruction to the specified cell. It will never send one type of instruction to the other type of cell. If they do so the body will stop functioning.

And also as a book when becomes older, its pages gradually tears and discolors and the written words on it become fade, we cannot read it clearly or cannot send any clear instructions from it, similarly, when we grow older our DNA also grow older, its genetic instructions also become fade and it cannot send the clear instructions properly.

This is why, when we gradually become older, we start suffering from various types of physical or medical problems.

From Human genome, the Human Genome Project, has acquired the sequences of the words produced with the chemical letters, and also identified their exact locations in the arms of “p” or “q” of Chromosomes, and saved as maps data-base wise.

The scientists, so far, could have saved the database of 12800 genes. But the databases of lot of genes, yet, could not have been discovered, and it is also unknown what kind of instructions sends these undiscovered genes in the body. It will take many more years to know their functions.
They have known that each gene has a specified location called “loci” and also a specified function.

Our genes also instruct how our body will develope, how much we will develop, how we will look, what color will be of our skin, eye or hair, how much we will be in height, what type of size will be of our nose and face, how much will be our talent etc.

To produce a specified protein, a gene may have hundreds of chemical code-words.

These genes are visible on the DNA thread like beads one after another with gap in between.

The DNA code remains in this beads set on DNA thread. These beads occupy only 1% of the total DNA thread. This part of DNA is called the “Coding DNA”.
The rest 99% of the DNA is called the “Noncoding DNA or Junk DNA”. (2)

Scientists believe that this greater part, the JUNK DNA, does not contain any code for instruction to run life.
The scientists could not yet have known what function this junk DNA does except very little.

They have little known that this part performs the function of “Switch On and Switch Of” and helps biological information for forensic medicine

What are “SWITCH ON” and ‘SWITCH OFF”?
When a gene is activated to produce a specified protein needed for body function is called “Switch On”.

And when not needed it is inactivated, that is called “Switch Off”, just like as we make “on” or ‘off” our electric valve of our house according to our need.

Suppose, our body have many types of different kinds off cells like, Skin cell, Heart muscle cell, Kidney cell, Liver cell, Neuron cell etc. Their functions are also of different kinds. And at the same time, all of them have the same DNA and gene.

It means in Heart muscle cell, there are also genes of liver cell, Kidney cell, and Neuron cell and so on, similarly in other cells also.

Now the question is, will the gene for liver cell function in the heart muscle cell?

The answer is “no”. It will be “Switch off’ there. Similar happens in other types of cells also, otherwise the biological activities of our body would shut down and we could not survive.

So the specified genes for specified cells are kept “Switch On” and others are kept “Switch off’. (2,5)

Scientists believe this control is done by the “Non Coding or Junk DNA”

Then you have already observed that our life depends not only on food, but it is the DNA that keeps us always alive and dynamic by working all the time to maintain all of our fine and complex biochemical activities inside the cell charging no cost from us. So we don’t have to cost any price or medicine for their activities. If their activities would depend upon any type of cost, not only the human, no life could survive on this globe.

Say, what happened for us if the responsibility of the 100 Trillion of cells’ function would impose upon ourselves?

Yes, we are very fortunate that they keep us all the time alive complying their duties nicely beyond our knowledge for 24 hours since the start of zygote till death. So we can fully pay our attention to earn our livelihood. Yet, how far could we do to improve our life and society?

All the genes of our body do not remain “Switch On” or “Switch Off” all the time.

There are some genes which remain active only till the baby delivers. They remain “Switch off” all over the life in the DNA, since they have no function after delivery. They work to produce differentiated (specialized) cell from Stem cell in the Uterus.
They are made “Switch off” and seated idle because they remain nothing to do after delivery. Look, how discipline they have to maintain. We being human, also cannot be so much sincere or respectful to our rules and regulations

If we would become such respectful to the rules and regulations, our society or nation would reach to a higher rank of a developed nation.

The main key for development of the developed nation underlies only upon their discipline, obedience and sincerity to their rules and regulations. Whoever remaining at any position can do nothing against rules and regulations. They believe their responsibility for people as a holiest work. Bribery or biasness does not work there.

Some people blame America for their strict rules and regulations, for example, an American president has also to appear on judicial court before judge to explain his deeds.

They cannot think such that America is remaining as an “America” since they maintain discipline and follow strict rules and regulations otherwise America would convert into Africa or Asia.

Such are also Europe and Australia.

A family or a nation must be a failure one where there is no respect for discipline.

See a particular example how DNA sends instruction for work.

DNA performs different types of activity of the body sending different types of genes in each different variety of cells.

Let us consider the case of Thyroid gland that remains in front of the throat.

This specified cells of this gland produces a hormone called Thyroxine (T3 and T4) and always supplies to our body for metabolic activity without cost.
Without this hormone our body cannot produce energy even if we eat enough, we will become gradually weaker and weaker and advance towards death unless the disease is diagnosed in time and treated with the artificially synthesized Thyroxine with proper dose every day.

It is to remember that the price of this scientifically synthesized Thyroxine is too high. Not everyone can bear its high cost in our country. But the developed countries insure all the medical costs for its citizen.
In our country this facility has yet not grown up. We hope our government would arrange this facility for our people in near future.

Let us come to our main issue. To synthesize Thyroxine, Thyroid cell needs a particular amino acid called “Tyrosine” along with other element like Iodine. This Tyrosine amino acid is at position 22 number.

Let us see now, which chemical code does the DNA use to supply Tyrosine to the thyroid cell to synthesize Thyroxine and how?

From left, at the top on third column remain 2 CODONs, “UAU” and “UAC” that is used to synthesize Tyrosine amino acid. DNA will transcribe (look chapter-3) any of these 2 CODONs and send through RNA (figure-5) to Ribosome, an organelle in Cytoplasm. A RNA of Ribosome called Translation RNA or tRNA will decode this CODON into language as Tyrosine amino acid and ask Ribosome to synthesize the Thyroxine. (3,4)

Then Ribosome synthesizes Tyrosine amino acid and supplies it to Thyroid cell. Then Thyroid cell synthesizes this most valuable Thyroxine hormone for us if all other situation is compatible.

To see how the Ribosome synthesizes protein decoding the DNA message by tRNA go through the chapter-11.

It is to remember that Ribosome works as a protein synthesizing factory in cell cytoplasm.
Here it is also to remember if any way, as the action of ultraviolet ray or the chemical compound like, Benzo-a-Pyrene of smoking, destruct the CODONs for Tyrosine, “UAU” and “UAC”, DNA will be unable to synthesize Thyroxine.

Such change in DNA is called Mutation. To learn Mutation, go through the chapter-12.
But, since the cell have 2 chromosome books, one from father and one from mother, the other book takes the responsibility to run normal body work, just as if our father dies, our mother takes the responsibility to run our family.

Thus keeping 2 chromosome books in the cell, our internal safety heightened more just as they give us safety also when they grow us up.

In other way, our parents are observing their responsibility in securing our life both externally and internally all the time.

Figure- 4, Ribosome, the protein factory.

Figure source-
Figure-5, RNA, how they carry CODON from DNA.

Keep in touch to learn the mystery of human body.

The references of chapter-9

[ ইংরেজীতে প্রকাশিত করা হল কিছু কিছু বাংলাদেশী বংশোদ্ভূত বিদেশে অবস্থানরত ছাত্র পাঠকেরা যারা বাংলা ভাষা পড়তে পারেনা, তাদের অনুরোধে, দুখিত ]

Chapter 10, What is DNA? What language has DNA used In Chromosome-Book? When DNA and protein are alive Robot.

1) Francis Harry Compton Crick (left). (Birth, June 8 1916- death. July 28, 2008)- an English molecular biologist, biophysicist, neuroscientist, the discoverer of CODON.

2) James Dewey Watson- (April.6, 1928, Chicago, IL, USA)(middle) affiliation at the time of the award: Harvard University, Cambridge, MA, USA.

3). Maurice Hugh Frederick Wilkins- (Birth -december-15, 1916, Pongaroa, New Zealand
Death: October 5, 2008, London, United Kingdom)(Right)

This scientist trio earned Nobel Prize in Physiology or medicine in 1962. (1,2,3)

We have to remain at least a little gratitude to these scientists for their contribution in medicine.

Let us now see what language has DNA used to write letters, words and sentences in writing genetic instructions on its Genetic-Book pages? Is it written in English, France or German language? Is there any space in between the words? How will it separate from one sentence or instruction from another? From which side will it begin reading from right or left? We are to observe all these issue in detail.

Let us observe now these issues thoroughly.

How many letters are there and what do they mean?

There are 4 letters-A, U, (or T), G and C.

These 4 letters indicate 4 Nucleotides as-

1)A=Adenine Nucleotide
2)U=Uracil Nucleotide. (In place of Thymine in DNA)
3)G=Guanine Nucleotide.
4)C=Cytosine Nucleotide.
(6) See chapter 2 and 3.

How a word is made? How many words are there in total?

Words (CODONs) are 64 in total. Each word is made with any of these three letters.

Then the total number of words will be 4x4x4=64 mathematically. This trio-letter word is called CODON as AUC, AGC, UGC etc. (1), See chapter-3

Yes, to understand the meaning of DNA’s word, see the dictionary of DNA (below figure-2). Out of 64 words, 61 mean 20 standard amino acids (protein unit). Since 20 amino acids are indicated by 61 CODONs, it means that 1 amino acid is indicated by more than I codon.

The rest 3 are used for other purposes. Now see the table below (figure-2) how DNA explore the meaning of the CODON or word.

You could ask there were many other compounds like carbohydrate, fat etc., why did DNA choose only protein excluding others, to operate body function?

Answer, since there is a great difference between protein and other compounds protein is such a compound that if it is synthesized following specified formula it is able to perform specified purpose. The other compound does not have such quality.

These proteins are very dynamic. Each of them seems to be an alive-Robot. Their activities show they possess sense and conscience. They are always expressing these qualities during their each performance. DNA would be inactive without these proteins just like as the Prime Ministry office would be action less without its helping other Ministry offices.

It is observed that the proteins synthesized with the formula of DNA code, can perform spontaneously complex works combinedly, collectively and coordinately.

It also seems, it is well known to DNA, which specified protein will act appropriately for which specified function and DNA synthesizes that specified protein with the specified genetic code and sends it for specified function.

It is just as like as the central administrative office of a state sends, at a medical problematic area, those persons who are built in the formula of a medical college to solve medical problems , and at a site of electrical problems sends those persons who are built in the formula of engineering college to solve electrical problems.

These functions cannot be done with other compounds rather than protein.

The dictionary for decoding genetic codes.

Figure-2, CODON table, the dictionary of DNA.

See on the table UUU and UUC mean Phenylalanine amino acid, UUA and UUG mean Leucine amino acid and AUG means Methionine amino acid that also acts as a Start CODON.

UAA, UAG and UGA , these 3 act only as Stop CODON.(1)

You have already got the DNA’s decoding dictionary. Now let us see how the instruction sentences or gene are written on the pages of DNA book.

It was said earlier that, from the beginning of our life, all the instructions are written on the pages of 2 books of DNA as our luck. The only function of DNA is to copy and send as the instructions to operate body cell functions. DNA can’t add us anything more beyond the written subject as our luck. (1) See videos 1 and 2.

The table also shows that DNA produces 20 standard amino acids, the protein unit, using 61 CODONs

And DNA synthesizes innumerous proteins using these 20 standard Amino acids that are called “Gene Expression”. (To know “Gene Expression” see chapter- 11)

And those proteins are the only equipment to operate all body functions.

What is the difference between amino acid, the protein unit, and the protein?

Protein is synthesized by joining of amino acids, the protein unit, in together, as the different sizes of buildings are created by joining the pieces of bricks.

You may ask how many types of different qualities and sizes of proteins could be synthesized?

Answer, innumerous varieties of qualities and sizes of proteins could be synthesized that could not be expressed with any number of this world.

To synthesize them appropriately, DNA has also saved their correct formula as “gene” beforehand.

Then DNA synthesizes the protein having appropriate qualities for the appropriate cell function with its factory, the Ribosome.

This way, it is also proved that our life is governed by protein. Our life can’t operate without protein.

An interesting matter, the proteins synthesized with the formula of DNA in its own factory, reserves a surprising quality and capability.

For example to perform a complicated function in cell such as Cell Division, DNA Replication or Gene Expression or Immune Process correctly, it requires a group of protein to work in together coordinately.

During such activities, they have to work jointly at many stages and to maintain coordination among themselves, group wise at each stage.

It is surprising to know that while the first protein group works at first stage, a second protein group await aside work for the second stage till the first protein group finishes their works at first stage. And when the first protein group finishes its works, the second protein group starts for the work of second stage immediately. And so on continues next stages until the work completes.

By this way, to perform a complicated work in cells, a lot of proteins have to participate jointly and coordinately.

This way, the proteins perform all the complicated works in body.

Most possibly, this marvelous quality of protein underlies its specified formula prescribed by DNA with its genetic code.

Here it seems DNA has good knowledge that which formula’s protein would work correctly for which function, so DNA sends proteins accordingly.

Thus protein is always expressing its surprising capability.

Another example when any bacteria enter into our body, the immunity cells reserves its protein into memory. The body synthesizes protein against the bacterial protein called “antibody’. This antibody is also a specified protein called ‘Immunoglobulin’ synthesized by DNA in immunity cells. (To learn more see chapter-41)

So, you could see protein has tremendous capability and importance in our body. And DNA synthesizes it by sending instruction created with three-letter word called CODON.

We call this instruction the “Gene”.

Now let us see how does DNA generate these instruction sentences?

Let us try some sample sentences to see how the genetic sentences are made. You are to know, unlike the pages of our books, there are no spaces in between DNA words on the pages of DNA book. DNA does not need any space in between words, since DNA, unlike us, never use different number of letters to build a word.

DNA’s every 3 letters is a meaningful word representing any of the 20 standard amino acids as mentioned in its dictionary above. The number of words in an instruction may vary from hundreds to thousands according to instruction size. You can imagine DNA an alive micro Robot with highest technology. Its format is built in such a way that all the performances done by it would be well controlled and coordinately.

Let us see how DNA makes sentences.
Let us see a sample sentence where there is no space in between words and it has no meaning to us, but DNA can make it a meaningful sentence taking in its format of three-letter word, that we cannot do.

Cannot you understand the meaning of this sentence? But DNA can understand it. Let us submit this sentence to DNA. Look how DNA can make it a meaningful sentence.

DNA will understand from that sentence as

“The sun was hot but the old man did not get his hat”.

Look how DNA could make a nice meaningful sentence with three-letter words without any change of word.(4)

Then, is there any problem for DNA to send instruction to body?

Yes, think a little, still there are some problems there are thousands of instructions on the page of DNA book without any gap or para in between the instructions.

Now, how DNA could distinguish a particular instruction for body differentiating from another instruction?

Suppose, in the Pancreas there is a genetic instruction to synthesize a hormone called “Insulin” that prevents Diabetes, and there is also another genetic instruction to synthesize a hormone called Glucagon that enhances Diabetes.

Suppose, these 2 antagonistic instructions remaining side by side. (This is not the fact, only for example).

Then would DNA mix these instructions while instructing only for the hormone, Insulin?

If DNA mixes the antagonistic instructions, it will be a wrong instruction. Body would not be able to synthesize Insulin. The person will be attacked with Diabetes. If, by any way, such changes occur and persist long, is called “Genetic Mutation”. (For Genetic Mutation see chapter-12)

Let us now come back to the main issue.

So, never a healthy DNA will mix a gene with another one. See how it separates one gene from another.

DNA marks where the gene begins and where ends.

It is already told before it is the Ribosome which finally implements the instruction synthesizing protein obeying the rules and regulations. mRNA carries the coded instruction from DNA to Ribosome. Ribosome decodes it through tRNA and will start synthesizing amino acid not from any site but only from “Start CODON”, then will continue forward and end just up to the back of “Stop CODON”.

See the sentence below how instruction is selected.

Look above the sentence, the genetic instruction is set just like this on the pages of DNA book. Suppose, mRNA carries this section to the Ribosome for synthesizing protein. Then Ribosome will not synthesize protein from this whole section.

From the section, Ribosome will start synthesizing at “START CODON” (AUG), including it, and end up to the STOP CODON (UAA), excluding it, up to the CODON AGA (marked with ***, just before the STOP CODON (UAA)

Ribosome will not care for the CODONs beyond the Start CODON and Stop CODON.

Now we are to observe, from which side would the Ribosome start reading, right or left?
No, unlike us, they don’t know right or left.
For reading or to do anything they start from “5’Prime end and go ahead towards 3’ Prime End” (To learn more see chaper-2)
Now see how Ribosome has selected the sentence below from the section above.

Look, Ribosome has got the START CODON, AUG, (Red under lined) after 8 letters from 5’ PRIME END on left, from where it will start synthesizing protein, including the Start CODON, AUG. and will continue forward just up to the back of the Stop CODON, UAA, excluding it, where it got the first STOP CODON (Red under lined).

By this way Ribosome selects the correct part of instruction.

Then Ribosome will throw the rest of the instruction just as we throw the rubbish in dustbin. Are you thinking where would the cell get a dustbin? See the figure-4 of an animal cell below. There is an organelle, Lysosome, used for dustbin.

I think you have already understood how DNA operates our complex body function by synthesizing protein sending its instruction.

But it is impossible to do it for DNA alone. It has to be assisted by the other organelles of the cell like ENDOPLSMIC RETICULAM, MICROTUBULES, GOLGI etc. (See the figure below) just as like as the Prime Ministry Office of a state is assisted by the other Ministerial Offices.

Thus far you could understand what type of fine and high technology is used by DNA, as if it is an alive Robot!

Recently, the scientists of MIT (Massachusetts Institute of Technology) and Harvard Medical School have discovered a gene in human body, responsible to make us fattier. They said the persons who have “FTO” gene are likely to be fattier, since “FTO” gene remains active in their body to store fat rather than to burn it. (6)

Keep in touch to know the mystery of human body.

Chapter-11. What Is Gene? How DNA Implements Its Written Instruction? Ribosome, A Protein Factory.

[ ইংরেজীতে প্রকাশিত করা হল কিছু কিছু বাংলাদেশী বংশোদ্ভূত বিদেশে অবস্থানরত ছাত্র পাঠকেরা যারা বাংলা ভাষা পড়তে পারেনা, তাদের অনুরোধে,দুখিতঃ]

1)Albert Claude (left)
Birth: August 24,1898, Longlier, Belgium
Death:May 22, 1983, Brussels, Belgium

2)Christian de Duve(Middle)
Birth: October 2,1917, Thames Ditton, United Kingdom
Death: May 4,2013, Nethen, Belgium

3) George E. Palade (Right)
Birth: November 19.1912, Iasi, Romania
Death: October 7,2008, Del Mar, CA, USA

This scientist trio became Nobel laureate in Physiology or medicine in 1974 for discovering the Ribosome, the protein synthesizing factory, in cell cytoplasm. These scientists, with hard labor, have advanced the Medical science for human welfare. So, we should have at least a little gratefulness to them. In this chapter, it has been explained how DNA implements its written instruction upon body materially. (1)

What Is Gene? What Does It Do? How Does It Express Its Function?

Gene is a unit that carries the hereditary characters from one generation to the next. Gene is a segment of DNA composed of Nucleotides (What is Nucleotide? See chapter-2). DNA sends Gene as a formula for synthesizing protein. And our body operates its all function through these proteins (See chapter-10). A human gene could be composed of some hundreds to 200, 0000 Nucleotides.

Most of the human genes are nearly similar. Only a little quantity (less than 1%) differs with the variation of sequence. For this genetic variation, never one person could be similar to another person in this world. (2) (See chapter-8)

Each human cell contains 20.000 to 25,000 genes.

Now we will see how the gene creates a material protein effective for body, by using codes that is called GENETIC EXPRESSION. (3, 4)

Why Does Gene Synthesize Protein?

Gene synthesizes protein, because protein is everything of our body. Our muscles, bones, hairs, teeth. nails. hormones, enzymes etc. every things are produced with protein. Hormones and enzymes operate the biological activities of cell. DNA synthesizes the material protein by sending its genetic code written in the Genetic Book, through a very complicated path. The other organelle of the cell, in particular, Ribosome, have also to work jointly.

Let us now see the ways how DNA synthesizes protein.


Cell performs this function within nucleus. Here, the MESSENGER RNA (mRNA) copies a segment of DNA with an enzyme called RNA POLYMERASE and enters cytoplasm crossing the nucleus envelope. At this stage it is named PRECURSOR mRNA (5,6,7) (see video-1,2,3)( see fgure-2) (for description see chapter-3)

Figure source-
Figure-2. Here it is shown how mRNA copying a segment of DNA.

It means the DNA segment copied by mRNA is translated into language and then protein is synthesized according to the instruction.

This function is performed jointly in together with Ribosome, mRNA and tRNA, in cytoplasm.


PREPARATION FOR mRNA- Before starting Translation, mRNA needs some preparation, as-

  1. mRNA cuts out the part of the segment that contains the base coding no Amino acid, called INTRON keeping only the portion codes for Amino acid, called EXON.
  1. To make mRNA more stable and strong, an enzyme called POLY- A- POLYMERASE adds 100 to 250 Adenine nucleotides at the end of 3’prime end. This is called Poly- A –Tail. (8)

And the 5’prime end is tightened by covering it with Guanosine Triphosphate just like as the shoe less ends are covered with caps, that the inside materials cannot damage. What an intense type of care.

It seems that the cell has sense of precaution, if the mRNA remains unstable it would not tolerate the pressure to be imposed upon it during next hard work, it would rather tear and break failing its aim. (See the video 4,5)

After completing this process, the Precursor mRNA converts into Mature RNA or mRNA, a complete active mRNA.

Now look how the mRNA, tRNA and Ribosome synthesize protein working in together.

It is a micro substance looking like a 3-loop leaf. An enzyme called Amino Acyl tRNA attaches any of the 20 standard Amino acids at its OH group of 3’prime end. This compound is now a charged tRNA called Amino Acyl tRNA.

At the other end of this tRNA remains a specialized complementary arrangement called ANTICODON. When a tRNA touches its ANTICODON to a CODON on mRNA, immediately can know if this CODON is complementary to the Amino acid remaining at its other end.

So, it is obvious that the ANTICODON end of the tRNA works as an improved type of equipment.

Suppose, a tRNA holds the Methyl Amino acid at its one end, and from the CODON table (figure-5) we can know the code of Methyl Amino acid is “AUG”’.

When this tRNA will check the “AUG” CODON on mRNA, will immediately understand that mRNA is indicating to use the METHYL AMINO ACID remaining at its opposite end. Then Ribosome will choose that METHYL AMINO ACID of the tRNA and head to the next CODON.

By this way, Ribosome will not advance forward until the mRNA CODON matches with the Amino acid of the tRNA through its ANTI CODON.

How Does Ribosome Translate The CODON And Synthesize Protein?

At first, mRNA sets as a video tape on some place of the smaller part of Ribosome keeping the 5’prime end ahead and 3’prime end behind. It means Ribosome will start reading from 5’prime end towards 3’prime end.

Just like, as we start reading or writing English or Bengali from left towards right. DNA has selected a particular side to start reading as we also do for reading or writing.

Without specifying a particular side no function could continue. So, it is observable what type of high skill is required to operate the complex functions of body.

There are three especial places on the greater Ribosome named E.P and A. E means exit, P means peptide and A means Amino Acyl. They set from 5’prime end towards 3’prime end serially as E>P>A.

The entire process to synthesize protein is divided into 3 stages as-

1) INITIATION-it means start of the work. A protein called Initiation Factor starts the work when Ribosome finds the start CODON, AUG. Ribosome will never start work until it gets start CODON.

2) ELONGATION- In this stage Ribosome will continue work until it gets stop CODON.

3) TERMINATION- it means finishing of the work. Finishing is done by a protein called Termination factor when Ribosome finds the stop CODON.

By this way DNA has limited Ribosome a particular area on mRNA to synthesize protein – from where to start and where to stop. Ribosome can do nothing beyond this limit.

Here also DNA shows another high skill. All the function would go useless if DNA would not have such limiting control upon Ribosome’s function. .
Ribosome moves ahead over the tape of mRNA from 5’prime end towards 3’prime end checking the CODONs.

Ribosome cannot start work until it gets the start CODON, AUG. when it finds the start CODON, the enzyme Initiation factor starts the work.

Then, at the Elongation stage, Ribosome continues work forward until it finds any stop CODON as UAA, UAG or UGA.

When Ribosome finds stop CODON, the enzyme, Termination factor comes and stops the protein synthesis.
Then an enzyme called Release factor comes and releases mRNA from Ribosome.

By this time, all the Amino acids synthesized are already joined in together by peptide bonds, maintaining sequence, forming protein. Stop CODON can synthesize no protein.

Now The Process Would Be Clear With An Example.

Suppose a CODON sentence is set on mRNA as below-

Now this mRNA will set at some place on smaller Ribosome like a tape. The Ribosome will start reading the mRNA from 5’prime end and go ahead towards 3’prime end. When it will get the start CODON, AUG, after passing the first 3 CODONs (UCU, CCU, ACU), will start synthesizing Amino acid. At this time, the greater Ribosome will bring its P part on the start CODON, AUG. Then the Initiation factor will start the function.

This is the first time Ribosome will bring a tRNA charged with Methionine Amino acid at P place on the start codon AUG. This Methionine will match with the CODON, AUG, since AUG also means Methionine according to the DNA dictionary.

So this tRNA carrying Methionine will first hold at P place of the greater Ribosome on the AUG CODON of mRNA.

Now the Ribosome will go a little forward and hold the A part on the CODON, UUU meaning Phenyl alanine. (Follow the CODON sentence above and the CODON table below, figure-5)

By this time, many other tRNA charged with other Amino acids will try to sit on this A place, but they will fail since their ANTICODON will not match with the mRNA’s CODON, UUU. The only tRNA will be allowed to sit here which contains Phenyl alanine wanted by mRNA’s CODON, UUU.

Now the Ribosome will detach the Methionine amino acid from the P- place- tRNA and join with the Phenyl alanine amino acid of A-place- tRNA, with peptide bond. Now the Amino acid- less tRNA of P place will be taken at E place and thrown into dustbin, since it has no use now.

At this time, the A-place tRNA still holding the Methionine and Phenyl alanine Amino acid will be moved at P place.

Now the A place is vacant. Ribosome will now move a little ahead and hold it’s A place on the mRNA’s next CODON, CUU meaning the Amino acid, Leucine.

At this time also the tRNA carrying Leucine Amino acid will be capable of siting at the A place of Ribosome.

Now the Methionine and Phenyl alanine Amino acid held by the tRNA of P place will be detached and joined with the Leucine Amino acid held by the A place tRNA with peptide bond.

Then again the Amino acid- less tRNA of P place will be moved at E place and thrown into dustbin. Now the Ribosome will bring the A- place tRNA holding the so far synthesized three Amino acids (Methionine, Phenyl alanine and Leucine) at P place. The A place is now again vacant.

Now possibly you have already understood what the Ribosome are going to do next.

Ribosome again will move a little forward and hold it’s A place on the next CODON, AUU meaning Isoleucine, one of the 20 standard Amino acid.

. ( Follow the CODON sentence above and the CODON table below,figure-5)

At this time also the tRNA carrying Isoleucine will be able to sit on A place. The 3 Amino acids attached to the P place tRNA will be released and attached with the Isoleucine of A place tRNA through peptide bond.

Then the Amino acid- less tRNA of P place will be moved at E place and thrown into dustbin and the A- place-tRNA holding 4 Amino acid (Methionine +Phenyl alanine+ Leucine + Isoleucine) will be taken at P place.

Again the A place is now vacant. Now the Ribosome again will move a little forward and hold it’s A place on the next CODON, GUU meaning Valine, one of the 20 standard Amino acid.

You could understand easily, here also only the tRNA carrying Valine Amino acid will match for sitting. The 4 Amino acids of P place will be joined with the Valine.

Now the synthesized 5 Amino acids (Methionine +Phenyl alanine+ Leucine + isoleucine+Valine) are attached at A- place-tRNA. The Amino acid-less- tRNA will be taken at E place and thrown into dustbin.

The A-place-tRNA attached with those 5 Amino acids will be taken at P place.

As before, Ribosome will proceed a little and hold it’s A place on the next CODON, UAA, of mRNA. As UAA is a stop CODON and means no Amino acid, Ribosome will stop protein synthesis and, by this time, all the Amino acids synthesized so far joined in together and converted into a protein.

Now an enzyme called Termination factor will come and declare the finishing of protein synthesis.

At this time, another enzyme called release factor will come and release mRNA from Ribosome, since the function of mRNA finished.

You have already observed what type of high technology DNA uses to limit its function within a specified area to synthesize its instructed protein!!

Let us now go a little back DNA sent through mRNA a coded section of gene as an instruction to synthesize a specified protein as,

Ribosome produced and gave the shape of that instruction into 5 Amino acids orderly as-


Now this is a real protein. This is the factual fruit of DNA’s instruction.

By this way DNA expresses its hidden code as visible and useful matter that is called “GENE EXPRESSION” in scientific language.

Why Does Body Need This Protein?

The entire compound like blood, muscle, bone, teeth, hair, organs of our body is made up of protein. Without protein they could not grow or develop. Even the organ and parts of our body could not develop without protein. (13)

Moreover, this protein with different names and forms like Hormone, Enzyme, Co-enzyme perform various biological purposes in various places, without which our body could not operate even a moment.

And Who Is Manufacturing That Protein?

Answer- DNA is doing through GENE EXPRESSION.

You have already observed the way these proteins are manufactured is not so simple, plain or easy rather they have to cross over a dreadful and gruesome path to be effective.

We have to suffer many complicated diseases if they are victimized at any place on this terrible way. It happens mostly when we grow older, since DNA also grow older in parallel with our age. At our old age the capability of DNA reduces as our body capability reduces. This is why, we start suffering with many problems as our age advances older, including cancer,

Or it also happens, if the sequences of original instruction, by any way, change by mutation.
A protein synthesized by this way may contain hundreds to thousands Amino acids. Immediately after production, they remain as a long thread. It is now raw, weak and breakable. Protein cannot function at this unstable and breakable condition. Now with some special processing, they have to transform into a stable and non-breakable substance. This special processing is called FOLDING AND PACKAGING.
They cannot function until they are transformed into a three dimensional material by folding and packaging, or it will remain non-functional. They are sent to the target place packaged inside vesicles made with protein.

Just as the clothes and dresses produced from the cloth factory of Savar, Dhaka cannot be marketed immediately after production unless they are folded, packaged in plastic bags and shipped in trucks.

Endoplasmic reticulum, Golgi and Vesicles, remain attached with Ribosome for carrying these proteins. The proteins are being synthesized folded, packaged and then loaded into the carriers. Vesicles are used as plastic bags.

Folding of proteins is an important factor.

Many non-curable neurodegenerative diseases appear due to lack of correct folding of protein as-
Creutzfeldt-Jakob disease, Bovine Spongiform Encephalopathy (mad cow disease), Amyloid- related diseases as, Alzheimer’s disease hereditary Amyloid Cardiomyopathy or Polyneuropathy, similarly Intracytoplasmic Aggregation diseases as Huntington’s and Parkinson’s disease.(10)

When the carrier is loaded, sent at the target place and unloads the materials there.

Just like as the manager of the cloth factory of Dhaka, after folding and packaging his raw products, ships to markets inside the country or abroad like, New York, London or India.

There is no difference in between their functions.

Question- how quickly does the Ribosome synthesizes proteins?

Answer- Ribosome does not work as slowly as I described here. Could the body operate if the Ribosome would be so slow? Never!

In case of human, Ribosome joins 6-9 Amino acids per second. If DNA sends a long mRNA, many Ribosomes complete the order working in together coordinately.

It woks quicker than the cloth factory.
Many antibiotic drugs used by the doctors today as, anisomycin, cycloheximide, chloramphenicol, tetracycline, streptomycin, erythromycin, and puromycin kill the bacteria by stopping protein synthesis in Ribosome.
But the drug cannot stop synthesizing proteins in the Ribosome of Eukaryotic animal like human, since their Ribosome is constructed in different way.

If the Ribosome of human would be like the Ribosome of Prokaryotic animal, human would die like bacteria after using antibiotic drugs.

Question- What Carriers Does The Cell Use To Carry Proteins?

Answer, the cells have many types of carriers inside, to carry the synthesized proteins as, Endoplasmic reticulum, Golgi apparatus, vesicles ctc. They use anyone that fits for the situation just as the manager of the Dhaka cloth factory uses.

I hope you have already understood how the DNA operates the body transforming its coded instruction into a three dimensional factual protein.

This process is called the GENE EXPRESSION. (6,7,8,9,10,11,12),see the video1-6. See the picture-3,4.
Source of figure-
Source of figure-

Figure-5, CODON TABLE, see the meaning of the codon mentioned above.

These complicated matters could not be clear without viewing videos.

See the videos below-

Keep in touch to know the mystery of human body.


Chapter 12, DNA. What is Mutation?

Nobel Laureates in 2015 in Medicine or physiology

[ ইংরেজীতে প্রকাশিত করা হল কিছু কিছু বাংলাদেশী বংশোদ্ভূত বিদেশে অবস্থানরত ছাত্র পাঠকেরা যারা বাংলা ভাষা পড়তে পারেনা, তাদের অনুরোধে,দুখিতঃ]

Nobel Prize in medicine or physiology in 2015 –

1) William C. Campbell (left) was born in 1930 in Ramelton, Ireland.

2) Satoshi Ōmura (middle) was born in 1935 in the Yamanashi Prefecture, Japan and is a Japanese Citizen.

3) Youyou Tu (Right) was born in 1930 in China

Their discovery of new medicines-

William C. Campbell and Satoshi Ōmura discovered a new drug, Avermectin, against parasites like Round Worm, Lymphatic Filariasis and many other types of worms.

Youyou Tu discovered a new drug , Artemisinin, against Malaria a drug that has significantly reduced the mortality rates for patients suffering from Malaria. (6).

Mutation is called the permanent change in sequence of DNA.

At which place of DNA can Mutation take place?

Mutation can take place at anywhere of DNA. For example on the 2 chains of DNA, there are 3 billions of base pairs, mutation can occur on any one of these bases or even along a segment of DNA. (View the Videos 1-4)
What would be the consequences of Mutation?

Gene sequence instructs protein sequence. So, when Gene sequences alter, protein sequences also alter.

You could just imagine DNA is the recipe of protein, if the recipe of our food is altered a little, the food will be altered accordingly. Exactly happens if the DNA sequence alters, the protein sequence will also alter.

In fact, the distinct quality and capability of a particular protein depends upon its distinct sequence. So, through the Mutation of DNA a large variation in animal kingdom may happen, over the globe.

Why human is growing from human?

Human is growing as human because human receive 23 pairs of distinct chromosomes having about 25,000 distinct genes, from their parents, only these distinct chromosomes and genes are responsible for making human as human.

Similarly, Horse has 64 pairs of distinct chromosome and thousands of distinct genes that are responsible for making Horses as Horse.

The Cow has 30 pairs of distinct chromosome and thousands of distinct genes that are making Cows as Cow.

Now you could imagine, some more developed and powerful creatures of some exoplanet have occupied our world, who has already earned the knowledge and technology how to turn the chromosome and DNA of one species of animal into another species of animal.

They will be experimenting to turn Cow and Horse into human and vice versa, making us their experimental animal in their animal farm laboratory, because, it is only the Chromosome and DNA which differentiate one species of animal from another species.

The scientists, based on this formula, have discovered the CLONING process, a world shaking discovery. Through this process you can make an exact copy of your beloved relatives or yourself and hold alive after your death in this world. (To know about cloning in detail see chapter-15)

So, the astronomy scientists should be careful of experimenting over exoplanets. If any more developed and powerful exoplanet inhabitant animal could get the information of our so resourceful world, could conquer us and use us as their laboratory experimental animal in their laboratory just like as we are doing with Guinea pigs, Rats, Sheep and Cows.

The natural Mutation changes the animal world very slowly fitting with the adverse effect of environment through diverse pathway altering chromosome and DNA sequences that the eyes of our short life is unable to catch.

The effect of Mutation through the change of DNA sequences can be of 3 types that sometimes can be only upon the person or sometimes passes to the next generations.

If the mutation occurs in somatic cell (other than sex cell) the effect limits only upon the person. And if the mutation occurs in sex cells the effect passes through the generation after generations that is called Inherited Mutation.

The effects of Mutation are of 3 types as-

At this situation the damage may be severe or a little. For example look at the figure-1 below. The middle CODON on the upper line was GAG meaning Glutamine, an Amino acid that synthesized Globin, a very important protein. This Globin produces the oxygen carrier, Hemoglobin mixing with Iron (Fe2+). It produces healthy RBC in blood.

Now look at the lower mutated line. Here the middle CODON, GAG is mutated into GTG meaning Valine, an Amino acid. (GTG=GUT)

So, now the produced protein will also change with the change in instruction. This changed or mutated protein in the attacked person will cause the production of abnormal size of RBC leading to Sickle Cell Anemia, a serious type blood deficiency disease. (See video-3)

Figure-2, the gene of Sickle cell anemia caused by mutation.

For example, sometimes body acquire immunity producing the protein, Immunoglobulin against microbial through genetic mutation.

More elaborately, suppose, some of your Arabian friends came at your house and stayed as guest with your close family contact. They were looking quite healthy.

After 2 weeks they left. Everything OK, no problem arose.

But after 2-4 weeks, it might happen that all of you were attacked with Mers Flu virus and died, and the disease spread at you area epidemically.

Your Arabian friends were attacked in past with Mers virus spread out from Arabian camel. But the DNA of their body, through mutation, saved them from the disease producing antibody against the virus. Or they got this mutated gene from their fore fathers. Now they are not sufferer from the disease, only as a carrier, dispersing the viruses at nearby surroundings, not being attacked themselves.

When they came at your closer contact, anyway, their virus entered into your body. And as your body did not have antibody against the virus, were attacked easily.

It is said the Mers virus spread through the nasal secretions, but scientists could not have yet discovered the real pathway.

Similarly, the Arabian Camels have been resistant growing antibody against the virus and spreading the disease as carrier around their surroundings, for what the Saudi government have adopted a ban on Camel sacrifice in the HAJJ ritual of 2015.

On the same way, the microbes also grow resistant against some antibiotics. Then that antibiotic cannot kill that microbe. For example, in some countries of Africa the Malarial parasites have grown antibody against Quinine drug through genetic Mutation.
In our country also, many higher antibiotics cannot work properly as did before.

Scientists have to discover new antibiotics time- to- time. This is called DRUG RESISTANCE.

How do the microbes become resistant?

What happens when microbes are exposed to antibiotics in the body? A group those who are in prior resistant survive, and those who are not resistant, some of them are killed and some of them grow antidote against the antibiotic through genetic mutation.

Then the antibiotic cannot kill them because they are now resistant to that antibiotic. Now all the generations emerge from them also does have the same resistance property.

By this way the antibiotic resistant microbes spread in the population.

As you have already seen above the scientist trio earned Nobel Prize in 2015 discovering new drugs against Parasites like malarial, Filariasis etc.

In our country, the microbes are growing antibiotic resistant promptly because the people can buy antibiotics from any pharmacy like grocery item without any prescription from registered physician since our Drug Administration Agency have no control over antibiotic or specified group of drug selling.

In advanced countries, none can collect from pharmacy even an antibiotic tablet without any prescription from a registered physician.
We hope, in near future, the antibiotics and specified drugs would come under Drug Administration control in our country also.
In fact, the animal kingdom always attempts to survive their generations in the opponent environment, through genetic Mutation.

For example, suppose, through very little and slow environmental change, the land of our world start drowning under ocean water along 100 thousand years.

What would then happen then?

All the living creature would die?

The answer is “NO”, all would not die.

When such environmental changes occur slightly and slowly, the animal kingdom also grows capacity to live in the opponent water environment through genetic mutation along generation to generation very slowly.

Some group will try to survive over mountain.
The group which could not grow this genetic change would vanish.

I am not saying that if the land sinks under the ocean today, the animal kingdom would start surviving tomorrow though Mutation.
It would require 100 and 100 thousand of years to take place the DNA mutation.

it cannot be experimented in laboratory.

But this globe itself is working as a big experimental laboratory along a long period beyond our view.

If any intelligent animal of 50-60 hundred thousand years of longevity lived in this globe, could easily view the mutational change occurring in short lived animal.

They could view how were looking the forefathers of human 50-60 hundred thousand years ago. For a very short lived creature like us is quite impossible to view such changes.

For having very short life, everything seems unchanged to us.

For example, the Dhaka City would seem unchanged to a person who is viewing the City only a year long.

On the other hand, the city would seem changed a lot to a person who had been viewing the city since 100 years long.

Then you could see how the 2 views differ with the difference of their duration of views.

The changes in animals occur along thousands and thousands yearlong slowly matching the adverse effect of environmental changes.

But you could view the changes occurring in insects at an environment around you with a 2-4 yearlong observation..

As A Personal Observation.

At our residence, in particular at kitchen, we can see a lot of small black insects looking somewhat like little cockroach. They enter into food pot in refrigerator whenever get chance. They are very boring. They run away or jump downwards from the desk very quickly whenever they can hear or recognize our arrival sounds there.

At earlier we could see no wings with them. But after 4-5 years, they have grown small wings that are using while they jump downwards and have also grown a little bigger in size looking some of them somewhat like small Cockroach and some of them somewhat like Fly.

It seems some of them are going to change into Cockroach and some into Fly.

It is observed only by me not by other family members

Just like this, the evolutionary process is always going on in small insects around our environment. I have also observed it occurring in fishes at my closed pond.

Anyone can view this changes in short lived small insects around our environment if he puts an observable eye upon it.

3) Sometimes the change of CODON does not have any effect upon the animal, either bad or good.

For example look at gene below-

AUG GUC TAG CAU – Before Mutation
AUG GUG TAG CAU – After Mutation

Look here, on the 1 st line on the 2 nd position there remains the CODON, “GUC” before Mutation.

And on the 2 nd line it turns into the CODON, “GUG” after Mutation.

This kind of change will bring no Mutational change because here both the CODON, “GUC” and “GUG” mean the same Amino acid, Valine . (figure-3) (2,3,4,5)
Source of Figure-

Mutation occurs in 2 processes-

  1. If any physical agent like Ultra Violet Ray, Radiation, a chemical agent like Benzo a Pyrene of Cigarettes strike and break the chemical bond of DNA structure , the DNA structure break , tear and mutate.

Figure-4, correct DNA structure on left, Mutated DNA structure on right.

Look here, on the left, 2 Oxygen bonds in phosphate back bone have torn by the strike of any agent and a part of DNA separated forming a Mutated DNA, shown on right.

  1. We grow through the continuous division of our body cells. While dividing a cell, the DNA of each of 100 trillion of cells has also to divide through a very complicated process inside the Nucleus (See the chapter7 and 8).

A lot of change might happen during this division. (See the figure -5 below)

Figure-5, joining of incorrect base during division.

Look here, the top DNA is copied into 2 on bottom. On the left, the base pairs (C-G,G-C, and T-A) have been copied exactly as it was in parent gene.

But on the right side, it is copied wrongly. Here, on first, it has put TG, which had to be CG just like the parent gene.

Moreover, G (GUANINE) cannot join with T(THYMINE) base. G (GUANINE) base always should join with C (CYTOSINE) base. (See chapter-2) (2-5) (see video-1,2,3,4) Relation between Evolution and Mutation.

Scientists have got enough proofs that mutational change in chromosome and DNA occurs when evolutionary change starts in animal. I told earlier that DNA is the recipe or formula of animal production. So if any changing wished in a product, the formula of the product should be altered beforehand because anything could not be produced without formula.

An Example By The Scientists

Chimpanzee like animals has 24 pairs of chromosomes.

The human have 23 pairs of chromosomes.

DNA experts believe sometimes a new type of animal evolves mutating the chromosome through joining 2 chromosomes into one.

For this favor, scientists strongly believe that the human chromosome no 2 has formed through joining of 2 Chimpanzee chromosomes end to end because the human chromosome no.2 contains exactly the similar genes as in the 2 chromosomes of Chimpanzee. (5) Look at the figure 6, 7 below.

Figure- 6, on left, the 2 separate chromosome of Chimpanzee. On right the human chromosome no 2 formed by joining 2 Chimpanzee chromosomes end to end.

Related Links

Are eukaryotic cells unicellular or multicellular?

Eukaryotic cells may be unicellular or multicellular. Paramecium, Euglena, Trypanosoma, Dinoflagellates are unicellular eukaryotes. Plants and animals are multicellular eukaryotes.

What is the most important characteristic of eukaryotic cells that distinguishes it from prokaryotic cells?

Eukaryotic cells have a membrane-bound nucleus. On the contrary, prokaryotic cells lack a true nucleus, i.e., they have no nuclear membrane. Unlike eukaryotic cells, the prokaryotic cells do not have mitochondria, chloroplast and endoplasmic reticulum.

Are viruses eukaryotes?

Viruses are neither eukaryotes nor prokaryotes. Since viruses are a link between living and non-living they are not considered in either category.

What are the salient features of a eukaryotic cell?

A eukaryotic cell has the following important features:

  • A eukaryotic cell has a nuclear membrane.
  • It has mitochondria, Golgi bodies, cell wall.
  • It also contains locomotory organs such as cilia and flagella.
  • The nucleus has a DNA that carries all the genetic information.

How does a eukaryotic cell divide?

A eukaryotic cell divides by the process of mitosis. It undergoes the following stages during cell division:

When did the first eukaryotic cell evolve?

The first eukaryotic cells evolved about 2 billion years ago. This is explained by the endosymbiotic theory that explains the origin of eukaryotic cells by the prokaryotic organisms. Mitochondria and chloroplasts are believed to have evolved from symbiotic bacteria.

What is the evidence for endosymbiotic theory?

The first evidence in support of the endosymbiotic theory is that mitochondria and chloroplast have their own DNA and this DNA is similar to the bacterial DNA. The organelles use their DNA to produce several proteins and enzymes to carry out certain activities.