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Bioenergetics of bioconversions: is there a surplus of energy?


By bioconversion, I mean a microbial process during which resting cells are used in order to convert a substrate to a desired product, whithout cell growth. For example, in this paper, they used Lactobacillus reuteri to convert glycerol to 3-hydroxypropionaldehyde, while L. reuteri can't grow on glycerol. Basically, during bioconversions, cells produce energy for their metabolism, but do not grow.

The energy thus yielded by cells is supposed to ensure their energetical maintenance cost. I was wondering what happens to cells if the energy gain is superior to maintenance needs? Is there some kind of homeostatic regulation of the ATP/ADP ratio? If not, what could be the consequences of too much ATP?


Energy homeostasis

In biology, energy homeostasis, or the homeostatic control of energy balance, is a biological process that involves the coordinated homeostatic regulation of food intake (energy inflow) and energy expenditure (energy outflow). [1] [2] [3] The human brain, particularly the hypothalamus, plays a central role in regulating energy homeostasis and generating the sense of hunger by integrating a number of biochemical signals that transmit information about energy balance. [2] [3] [4] Fifty percent of the energy from glucose metabolism is immediately converted to heat. [5]

Energy homeostasis is an important aspect of bioenergetics.


Bioenergetics of bioconversions: is there a surplus of energy? - Biology

Kathleen M. Botham, PhD, DSc & Peter A. Mayes, PhD, DSc

After studying this chapter, you should be able to:

State the first and second laws of thermodynamics and understand how they apply to biologic systems.

Explain what is meant by the terms free energy, entropy, enthalpy, exergonic, and endergonic.

Appreciate how reactions that are endergonic may be driven by coupling to those that are exergonic in biologic systems.

Understand the role of high-energy phosphates, ATP, and other nucleotide triphosphates in the transfer of free energy from exergonic to endergonic processes, enabling them to act as the “energy currency” of cells.

BIOMEDICAL IMPORTANCE

Bioenergetics, or biochemical thermodynamics, is the study of the energy changes accompanying biochemical reactions. Biologic systems are essentially isothermic and use chemical energy to power living processes. How an animal obtains suitable fuel from its food to provide this energy is basic to the understanding of normal nutrition and metabolism. Death from starvation occurs when available energy reserves are depleted, and certain forms of malnutrition are associated with energy imbalance (marasmus). Thyroid hormones control the rate of energy release (metabolic rate), and disease results when they malfunction. Excess storage of surplus energy causes obesity, an increasingly common disease of Western society, which predisposes to many diseases, including cardiovascular disease and diabetes mellitus type 2, and lowers life expectancy.

FREE ENERGY IS THE USEFUL ENERGY IN A SYSTEM

Gibbs change in free energy (AG) is that portion of the total energy change in a system that is available for doing work&mdashie, the useful energy, also known as the chemical potential.

Biologic Systems Conform to the General Laws of Thermodynamics

The first law of thermodynamics states that the total energy of a system, including its surroundings, remains constant. It implies that within the total system, energy is neither lost nor gained during any change. However, energy may be transferred from one part of the system to another or may be transformed into another form of energy. In living systems, chemical energy may be transformed into heat or into electrical, radiant, or mechanical energy.

The second law of thermodynamics states that the total entropy of a system must increase if a process is to occur spontaneously. Entropy is the extent of disorder or randomness of the system and becomes maximum as equilibrium is approached. Under conditions of constant temperature and pressure, the relationship between the free-energy change (&DeltaG) of a reacting system and the change in entropy (&DeltaS) is expressed by the following equation, which combines the two laws of thermodynamics:

where &DeltaH is the change in enthalpy (heat) and T is the absolute temperature.

In biochemical reactions, since &DeltaH is approximately equal to &DeltaE, the total change in internal energy of the reaction, the above relationship may be expressed in the following way:

If &DeltaG is negative, the reaction proceeds spontaneously with loss of free energy ie, it is exergonic. If, in addition, &DeltaG is of great magnitude, the reaction goes virtually to completion and is essentially irreversible. On the other hand, if &DeltaG is positive, the reaction proceeds only if free energy can be gained ie, it is endergonic. If, in addition, the magnitude of &DeltaG is great, the system is stable, with little or no tendency for a reaction to occur. If &DeltaG is zero, the system is at equilibrium and no net change takes place.

When the reactants are present in concentrations of 1.0 mol/L, &DeltaG 0 is the standard free-energy change. For biochemical reactions, a standard state is defined as having a pH of 7.0. The standard free-energy change at this standard state is denoted by &DeltaG 0 ’.

The standard free-energy change can be calculated from the equilibrium constant Keq.

where R is the gas constant and T is the absolute temperature (Chapter 8). It is important to note that the actual &DeltaG may be larger or smaller than &DeltaG 0 ’ depending on the concentrations of the various reactants, including the solvent, various ions, and proteins.

In a biochemical system, an enzyme only speeds up the attainment of equilibrium it never alters the final concentrations of the reactants at equilibrium.

ENDERGONIC PROCESSES PROCEED BY COUPLING TO EXERGONIC PROCESSES

The vital processes&mdasheg, synthetic reactions, muscular contraction, nerve impulse conduction, and active transport&mdashobtain energy by chemical linkage, or coupling, to oxidative reactions. In its simplest form, this type of coupling may be represented as shown in Figure 11–1. The conversion of metabolite A to metabolite B occurs with release of free energy and is coupled to another reaction in which free energy is required to convert metabolite C to metabolite D. The terms exergonic and endergonic, rather than the normal chemical terms “exothermic” and “endothermic,” are used to indicate that a process is accompanied by loss or gain, respectively, of free energy in any form, not necessarily as heat. In practice, an endergonic process cannot exist independently, but must be a component of a coupled exergonic-endergonic system where the overall net change is exergonic. The exergonic reactions are termed catabolism (generally, the breakdown or oxidation of fuel molecules), whereas the synthetic reactions that build up substances are termed anabolism. The combined catabolic and anabolic processes constitute metabolism.

FIGURE 11–1 Coupling of an exergonic to an endergonic reaction.

If the reaction shown in Figure 11–1 is to go from left to right, then the overall process must be accompanied by loss of free energy as heat. One possible mechanism of coupling could be envisaged if a common obligatory intermediate (I) took part in both reactions, ie,

Some exergonic and endergonic reactions in biologic systems are coupled in this way. This type of system has a built-in mechanism for biologic control of the rate of oxidative processes since the common obligatory intermediate allows the rate of utilization of the product of the synthetic path (D) to determine by mass action the rate at which A is oxidized. Indeed, these relationships supply a basis for the concept of respiratory control, the process that prevents an organism from burning out of control. An extension of the coupling concept is provided by dehydrogenation reactions, which are coupled to hydrogenations by an intermediate carrier (Figure 11–2).

FIGURE 11–2 Coupling of dehydrogenation and hydrogenation reactions by an intermediate carrier.

An alternative method of coupling an exergonic to an endergonic process is to synthesize a compound of high-energy potential in the exergonic reaction and to incorporate this new compound into the endergonic reaction, thus effecting a transference of free energy from the exergonic to the endergonic pathway (Figure 11–3). The biologic advantage of this mechanism is that the compound of high potential energy,

/>, unlike I in the previous system, need not be structurally related to A, B, C, or D, allowing />to serve as a transducer of energy from a wide range of exergonic reactions to an equally wide range of endergonic reactions or processes, such as biosyntheses, muscular contraction, nervous excitation, and active transport. In the living cell, the principal high-energy intermediate or carrier compound (designated

in Figure 11–3) is adenosine triphosphate (ATP) (Figure 11–4).

FIGURE 11–3 Transfer of free energy from an exergonic to an endergonic reaction via a high-energy intermediate compound (

).

FIGURE 11–4 Adenosine triphosphate (ATP) and adenosine diphosphate shown as the magnesium complexes.

HIGH-ENERGY PHOSPHATES PLAY A CENTRAL ROLE IN ENERGY CAPTURE AND TRANSFER

In order to maintain living processes, all organisms must obtain supplies of free energy from their environment. Autotrophic organisms utilize simple exergonic processes eg, the energy of sunlight (green plants), the reaction Fe 2+ &rarrFe 3+ (some bacteria). On the other hand, heterotrophic organisms obtain free energy by coupling their metabolism to the breakdown of complex organic molecules in their environment. In all these organisms, ATP plays a central role in the transference of free energy from the exergonic to the endergonic processes (Figure 11–3). ATP is a nucleoside triphosphate containing adenine, ribose, and three phosphate groups. In its reactions in the cell, it functions as the Mg 2+ complex (Figure 11–4).

The importance of phosphates in intermediary metabolism became evident with the discovery of the role of ATP, adenosine diphosphate (ADP) (Figure 11–4), and inorganic phosphate (Pi) in glycolysis (Chapter 18).

The Intermediate Value for the Free Energy of Hydrolysis of ATP Has Important Bioenergetic Significance

The standard free energy of hydrolysis of a number of biochemically important phosphates is shown in Table 11-1. An estimate of the comparative tendency of each of the phosphate groups to transfer to a suitable acceptor may be obtained from the &DeltaG 0 ’ of hydrolysis at 37°C. The value for the hydrolysis of the terminal phosphate of ATP divides the list into two groups. Low-energy phosphates, exemplified by the ester phosphates found in the intermediates of glycolysis, have G 0 ’ values smaller than that of ATP, while in high-energy phosphates the value is higher than that of ATP. The components of this latter group, including ATP, are usually anhydrides (eg, the 1-phosphate of 1,3-bisphosphoglycerate), enolphosphates (eg, phosphoenolpyruvate), and phosphoguanidines (eg, creatine phosphate, arginine phosphate).

TABLE 11–1 Standard Free Energy of Hydrolysis of Some Organophosphates of Biochemical Importance

indicates that the group attached to the bond, on transfer to an appropriate acceptor, results in transfer of the larger quantity of free energy. For this reason, the term group transfer potential, rather than “high-energy bond,” is preferred by some. Thus, ATP contains two high-energy phosphate groups and ADP contains one, whereas the phosphate in AMP (adenosine monophosphate) is of the low-energy type since it is a normal ester link (Figure 11–5).

FIGURE 11–5 Structure of ATP, ADP, and AMP showing the position and the number of high-energy phosphates (

).

The intermediate position of ATP allows it to play an important role in energy transfer. The high free-energy change on hydrolysis of ATP is due to relief of charge repulsion of adjacent negatively charged oxygen atoms and to stabilization of the reaction products, especially phosphate, as resonance hybrids (Figure 11–6). Other “high-energy compounds” are thiol esters involving coenzyme A (eg, acetyl-CoA), acyl carrier protein, amino acid esters involved in protein synthesis, S adenosylmethionine (active methionine), UDPGlc (uridine diphosphate glucose), and PRPP (5-phosphoribosyl-1-pyrophosphate).

FIGURE 11–6 The free-energy change on hydrolysis of ATP to ADP.

HIGH-ENERGY PHOSPHATES ACT AS THE “ENERGY CURRENCY” OF THE CELL

ATP is able to act as a donor of high-energy phosphate to form those compounds below it in Table 11-1. Likewise, with the necessary enzymes, ADP can accept high-energy phosphate to form ATP from those compounds above ATP in the table. In effect, an ATP/ADP cycle connects those processes that generate

to those processes that utilize

(Figure 11–7), continuously consuming and regenerating ATP. This occurs at a very rapid rate since the total ATP/ADP pool is extremely small and sufficient to maintain an active tissue for only a few seconds.

FIGURE 11–7 Role of ATP/ADP cycle in transfer of high-energy phosphate.

There are three major sources of

taking part in energy conservation or energy capture:

1. Oxidative phosphorylation. The greatest quantitative source of

in aerobic organisms. Free energy comes from respiratory chain oxidation using molecular O2 within mitochondria (Chapter 12).

2. Glycolysis. A net formation of two

results from the formation of lactate from one molecule of glucose, generated in two reactions catalyzed by phosphoglycerate kinase and pyruvate kinase, respectively (Figure 18–2).

3. The citric acid cycle. One

is generated directly in the cycle at the succinate thiokinase step (Figure 17–3).

Phosphagens act as storage forms of high-energy phosphate and include creatine phosphate, which occurs in vertebrate skeletal muscle, heart, spermatozoa, and brain, and arginine phosphate, which occurs in invertebrate muscle. When ATP is rapidly being utilized as a source of energy for muscular contraction, phosphagens permit its concentrations to be maintained, but when the ATP/ADP ratio is high, their concentration can increase to act as a store of high-energy phosphate (Figure 11–8).

FIGURE 11–8 Transfer of high-energy phosphate between ATP and creatine.

When ATP acts as a phosphate donor to form those compounds of lower free energy of hydrolysis (Table 11-1), the phosphate group is invariably converted to one of low energy, eg

ATP Allows the Coupling of Thermodynamically Unfavorable Reactions to Favorable Ones

The phosphorylation of glucose to glucose 6-phosphate, the first reaction of glycolysis (Figure 18–2), is highly endergonic and cannot proceed under physiologic conditions:

To take place, the reaction must be coupled with another&mdashmore exergonic&mdashreaction such as the hydrolysis of the terminal phosphate of ATP.

When (1) and (2) are coupled in a reaction catalyzed by hexokinase, phosphorylation of glucose readily proceeds in a highly exergonic reaction that under physiologic conditions is irreversible. Many “activation” reactions follow this pattern.

Adenylyl Kinase (Myokinase) Interconverts Adenine Nucleotides

This enzyme is present in most cells. It catalyzes the following reaction:

1. High-energy phosphate in ADP to be used in the synthesis of ATP.

2. AMP, formed as a consequence of several activating reactions involving ATP, to be recovered by rephosphorylation to ADP.

3. AMP to increase in concentration when ATP becomes depleted and act as a metabolic (allosteric) signal to increase the rate of catabolic reactions, which in turn lead to the generation of more ATP (Chapter 20).

When ATP Forms AMP, Inorganic Pyrophosphate (PPi) Is Produced

ATP can also be hydrolyzed directly to AMP, with the release of PPi. (Table 11-1). This occurs, for example, in the activation of long-chain fatty acids (Chapter 22).

This reaction is accompanied by loss of free energy as heat, which ensures that the activation reaction will go to the right and is further aided by the hydrolytic splitting of PPi, catalyzed by inorganic pyrophosphatase, a reaction that itself has a large &DeltaG 0 ’ of -19.2 kJ/mol. Note that activations via the pyrophosphate pathway result in the loss of two

rather than one, as occurs when ADP and Pi are formed.

A combination of the above reactions makes it possible for phosphate to be recycled and the adenine nucleotides to interchange (Figure 11–9).

FIGURE 11–9 Phosphate cycles and interchange of adenine nucleotides.

Other Nucleoside Triphosphates Participate in the Transfer of High-Energy Phosphate

By means of the enzyme nucleoside diphosphate kinase, UTP, GTP, and CTP can be synthesized from their diphosphates, eg, UDP reacts with ATP to form UTP.

All of these triphosphates take part in phosphorylations in the cell. Similarly, specific nucleoside monophosphate kinases catalyze the formation of nucleoside diphosphates from the corresponding monophosphates.

Thus, adenylyl kinase is a specialized monophosphate kinase.

Biologic systems use chemical energy to power living processes.

Exergonic reactions take place spontaneously with loss of free energy (&DeltaG is negative). Endergonic reactions require the gain of free energy (&DeltaG is positive) and occur only when coupled to exergonic reactions.

ATP acts as the “energy currency” of the cell, transferring free energy derived from substances of higher energy potential to those of lower energy potential.

de Meis L: The concept of energy-rich phosphate compounds: water, transport ATPases, and entropy energy. Arch Biochem Biophys 1993306:287.

Frey PA, Arabshahi A: Standard free-energy change for the hydrolysis of the alpha, beta-phosphoanhydride bridge in ATP. Biochemistry 199534:11307.

Harold FM: The Vital Force: A Study of Bioenergetics. Freeman, 1986.

Harris DA: Bioenergetics at a Glance: An Illustrated Introduction. Blackwell Publishing, 1995.

Haynie D: Biological Thermodynamics. Cambridge University Press, 2008.

Jencks WP: Free energies of hydrolysis and decarboxylation. In: Handbook of Biochemistry and Molecular Biology, vol 1. Physical and Chemical Data. Fasman GD (editor). CRC Press, 1976:296-304.

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Nicholls D, Ferguson F: Bioenergetics. Elsevier, 2003.

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Modification of Proteins by Reactive Ethanol Metabolites: Adduct Structure, Functional and Pathological Consequences

5-Deoxy-D-xylulose-1-phosphate (DXP) Adducts

Formation of DXP from acetaldehyde and fructose-1,6-bisphosphate was first demonstrated by Meyerhof et al. (1936) using muscle extracts to catalyse the reaction. The glycolytic enzymes aldolase and triose isomerase were believed to be involved. These enzymes are found in virtually every type of cell suggesting that most cells may be able to synthesize DXP if acetaldehyde is available. Evidence for the formation of DXP in the liver came from studies by Hoberman who showed that extracts of livers perfused in situ with [ 3 H]acetaldehyde contained a small amount of a highly acidic, phosphate-containing, non-volatile radiolabelled compound. Hoberman speculated that this compound was DXP formed by the action of aldolase on acetaldehyde and dihyroxyacetone phosphate and confirmed this by chromatographic comparison with chemically synthesized DXP. Hoberman further characterized the synthezis of DXP using erythrocytes, cells which actively undergo glycolysis to provide dihydroxyacetone phosphate in a system uncomplicated by the regulatory influences of mitochondrial respiration ( Hoberman, 1979 a). Later studies showed that DXP could react with haemoglobin to form an adduct which was stable to repeated precipitation by trichloroacetic acid ( Hoberman, 1979 b). This adduct is likely to be formed by a series of reactions similar to those of non-enzymic glycation. Initially the DXP probably forms a Schiff base on an amino group which then undergoes the Amadori rearrangement to finally yield a ketoamine adduct ( Fig. 6 ). The product contains an α-hydroxyketone group which can react with another amino group in a similar manner and could cause cross-linking if the second amino group was on a different peptide. Apart from the in vitro study showing that DXP reacts with haemoglobin to produce covalent modifications, there is no evidence to show that similar adducts are formed in vivo.

Figure 6 . A potential scheme for the formation of adducts by DXP.


Salish Sea Ecosystem Conference

The Fraser River Estuary is a major link in a chain of Pacific coastal habitats that support migrating and wintering waterfowl, and many birds converge here during northward and southward travels. Between 800,000 and 2.3 million waterfowl use the estuary from September through April, including significant populations of American wigeon, mallard, northern pintail, surf scoter, snow goose and brant. Waterfowl mainly use agricultural lands, freshwater and brackish wetlands, and intertidal habitats such as eelgrass beds, all of which continue to be lost or degraded by population growth and urban sprawl. We used a bioenergetic model (TRUEMET) to explicitly link waterfowl population objectives to habitat objectives for farmland conservation. TRUEMET indicates whether there is a habitat surplus or deficit for a given population level. We combined five of the most abundant species into two foraging guilds: ‘grazers’ included American wigeon and snow goose, and ‘dabblers’ included mallard, northern pintail and green-winged teal. We assessed conditions as of 2009 and tested a variety of scenarios involving changes in habitat availability, including future losses of agricultural or intertidal habitats. Model results indicated that grazers experienced an excess of energy through the nonbreeding season, but this was predicted to become to a deficit by midwinter within 20 years under likely scenarios. For dabblers, the demand exceeded supply by December, and the situation only worsened under future scenarios. Ensuring their continuing presence at current levels in the face of growing development stressors will require a multi-faceted conservation strategy for both intertidal and farmland conservation. We set a conservative foraging habitat objective of 50% of the energy needs of waterfowl on agricultural lands during the migrating and wintering periods, which equates to 15,000 x10^6 kcal of energy. From a habitat program perspective, this will require protecting farmlands and encouraging green forage cropping on the broader landscape.

Session Title

Shorebird Monitoring in the Salish Sea

Keywords

Water fowl, Bioenergetics, TruMet, Ducks Unlimited Canada

Conference Track

SSE7: Monitoring: Species and Habitats

Conference Name

Salish Sea Ecosystem Conference (2018 : Seattle, Wash.)

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SSEC Identifier

Start Date

End Date

Type of Presentation

Genre/Form

presentations (communicative events)

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Subjects – Topical (LCSH)

Waterfowl--Migration--Climatic factors--British Columbia--Fraser River Waterfowl--Habitat--Conservation--British Columbia--Fraser River

Geographic Coverage

Fraser River (B.C.) Salish Sea (B.C. and Wash.)

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This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534 [email protected]) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

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Using a bioenergetic model to set waterfowl habitat objectives for the Fraser River delta

The Fraser River Estuary is a major link in a chain of Pacific coastal habitats that support migrating and wintering waterfowl, and many birds converge here during northward and southward travels. Between 800,000 and 2.3 million waterfowl use the estuary from September through April, including significant populations of American wigeon, mallard, northern pintail, surf scoter, snow goose and brant. Waterfowl mainly use agricultural lands, freshwater and brackish wetlands, and intertidal habitats such as eelgrass beds, all of which continue to be lost or degraded by population growth and urban sprawl. We used a bioenergetic model (TRUEMET) to explicitly link waterfowl population objectives to habitat objectives for farmland conservation. TRUEMET indicates whether there is a habitat surplus or deficit for a given population level. We combined five of the most abundant species into two foraging guilds: ‘grazers’ included American wigeon and snow goose, and ‘dabblers’ included mallard, northern pintail and green-winged teal. We assessed conditions as of 2009 and tested a variety of scenarios involving changes in habitat availability, including future losses of agricultural or intertidal habitats. Model results indicated that grazers experienced an excess of energy through the nonbreeding season, but this was predicted to become to a deficit by midwinter within 20 years under likely scenarios. For dabblers, the demand exceeded supply by December, and the situation only worsened under future scenarios. Ensuring their continuing presence at current levels in the face of growing development stressors will require a multi-faceted conservation strategy for both intertidal and farmland conservation. We set a conservative foraging habitat objective of 50% of the energy needs of waterfowl on agricultural lands during the migrating and wintering periods, which equates to 15,000 x10^6 kcal of energy. From a habitat program perspective, this will require protecting farmlands and encouraging green forage cropping on the broader landscape.


A comprehensive review of the bioenergetics of fatty acid and glucose metabolism in the healthy and failing heart in nondiabetic condition

The function of the heart is defined by its ability to deliver adequate cardiac output to meet the requirements of the body both at rest and with exertion. To fill this role, the heart demonstrates an impressive capacity to tightly regulate energy generation and consumption. Energy production and transfer within cardiac myocytes primarily relies on the process of oxidative phosphorylation. In the failing heart, there is an imbalance between the work of the cardiac system and the energy required to generate this work. This presence of this mismatch has given rise to the concept known as the energy starvation theory. This concept encapsulates observations such as perturbed substrate consumption, insufficient energy transfer and ingestion, reduced substrate and oxygen availability, and diminished energy production in the failing heart. Diminished available cellular energy may further result from a reduction in the biosynthesis of mitochondria and their protein synthesis and from global cellular architectural disarray. In essence, the energy starvation theory posits that cardiac pump function declines due to a reduction in oxygen and substrate availability, and thus leads to a total body starvation of systemic energy. This novel cognitive framework has led to encouraging new directions in a “metabolic therapeutic approach” for the failing heart.

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Discussion

Patterns of sexual dimorphism in walleye and yellow perch were very similar, suggesting that comparable evolutionary forces and/or constraints may be acting on the life histories of both these closely related fishes. This is noteworthy, given the ecological differences between the species walleye are primarily piscivorous and on average live twice as long as perch, which are typically benthivorous/zooplanktivorous. This similarity in sexual dimorphism between species suggests that bioenergetic differences between male and female yellow perch described here also probably apply to walleye, and perhaps other species demonstrating similar life histories ( Roff 1983 ).

Our results do not support a previous hypothesis ( Henderson et al. 2003 ) that reduced male growth efficiency is due to increased activity associated with reproduction. Considering growth characteristics alone, one might conclude that males invest more in reproduction relative to females because estimates of male g-values were 1·2–1·3 times higher than those observed in females. For walleye and yellow perch (as well as other fish species), it has been shown that estimates of female g based on the biphasic growth model are correlated with (and approximately equal to) female gonadosomatic index ( Shuter et al. 2005 ). Because gonad production is a major energetic cost of reproduction in females, estimates of female g seem to provide a good measure of reproductive investment. A logical extension of this argument is that growth-based estimates of male g reflect reproductive costs of males. Thus, one might conclude that males attain a smaller asymptotic size because energetic losses associated with reproduction are higher for males than for females. If this were the case, then a bioenergetic analysis should reveal higher metabolic activity in post-maturation males. This was not supported by our study bioenergetic results for yellow perch indicate that the sex-related differences in growth rate are due to reduced energy acquisition and assimilation in males relative to females at the onset of maturity. Reduced male growth rate in sexually mature yellow perch and walleye cannot be explained by an activity hypothesis (i.e. more active males) because estimates of male total metabolic costs were lower than in females.

Our observation of decreased consumption and metabolic activity in male perch is consistent with Roff's (1983 ) hypothesis that smaller male size in teleosts relative to females (in the absence of territorial behaviour or parental care) is a selective response to increase survival by reducing foraging activity, presuming that increased activity entails increased predation risk. A previous application of the mercury mass-balance model also reported higher activity in female Esox lucius ( Trudel et al. 2000 ). The difference was not significantly greater than in males, but was based on a relatively small sample of populations. Similarly, an application of a 137 Cs model also reported higher activity in female E. lucius and Salvelinus namaycush based on a small (one to three) number of observations ( Rowan & Rasmussen 1996 ). Another study that examined mercury concentrations between genders in four species of centrarchid fish concluded that male foraging rates declined relative to those of females at the onset of maturity ( Nicoletto & Hendricks 1988 ). Our findings may also apply more generally to species where the smaller sex (male or female) displays reduced activity and foraging. For example, larger male Anax junius (damselflies) were found to be more active than smaller females during foraging trials ( Fuselier et al. 2007 ).

However, the hypothesis presented by Henderson et al. (2003 ) is not without support in the literature. Reproductively active male gerrids (hemipteran water striders) exhibited greater activity than immatures or mature females, but were also the poorest foragers ( Blanckenhorn & Perner 1996 ). Also, female Coenagrion puella (damselflies) were less active than males in the presence of food and predators, and emerged at larger sizes ( Mikolajewski et al. 2005 ). Given literature support for both the reduced foraging hypothesis ( Roff 1983 ) and the increased activity hypothesis ( Henderson et al. 2003 ), feeding and activity budgets should be considered together when attempting to explain proximate mechanisms of SSD.

Our results indicate that the onset of sexual maturity plays a major role in generating SSD in percids. Bioenergetic differences between male and female yellow perch were obvious only after the onset of maturity, when many organisms experience changes in endocrine activity. Laboratory experiments by Malison et al. (1985 , 1988 ) demonstrated that consumption and FCE differences between male and female yellow perch probably result from differential hormonal effects on males and females at the onset of maturation. In yellow perch, ovarian oestrogens stimulated and testicular androgens inhibited growth ( Malison et al. 1985 ). However, the effect was observed only in larger juveniles, suggesting that the action of these hormones would manifest in fish where a certain maturational status had been achieved. Growth and consumption of larger juvenile male and female yellow perch fed ad libitum both increased when individuals were exposed to oestrogens ( Malison et al. 1988 ). Consistent with our bioenergetic results, Malison et al. (1988 ) observed faster female growth, higher consumption and higher FCE relative to males regardless of oestrogen exposure level. Analogous negative effects of androgens on consumption and FCE have been documented in juvenile Eurasian perch (P. fluviatilis Mandiki et al. 2004 Mandiki et al. 2005 ), where consumption rates increased in females exposed to oestrogens and decreased in males exposed to androgens. The action of both these hormones (positive effect of oestrogens on female growth, negative effects of androgens on male growth) and the dependence of hormone action on perch developmental stage corresponds with our observed onset of SSD in yellow perch and walleye at sexual maturation. Hormonal activity has also been tied to changes in maturation status, SSD and metabolic rate in other taxonomic groups ( Cox et al. 2005 John-Alder, Cox & Taylor 2007 Wudy, Hartman & Remer 2007 ).

Bioenergetic submodels of consumption and respiration were parameterized originally under the assumption that males and females have comparable physiology ( Kitchell et al. 1977 ), and potential gender differences in these submodels have not been evaluated. Although published accounts show that standard metabolism and assimilation efficiencies can differ between males and females ( Shillington 2005 Valle et al. 2005 ), sufficient data are currently lacking to parameterize accurately gender-based submodels for consumption and metabolism in percids. However, our analysis best reflects the evaluation of gender differences between male and female fish given the manner in which these submodels were parameterized, as we examined residual differences of bioenergetic patterns from the common slope (across both sexes) with body weight. Clearly, this work calls for investigations into the dependence of bioenergetic and contaminant allometries on gender. In the absence of this information, our findings suggest that investigators use caution in interpreting bioenergetic results from models applied to both males and females in the absence of information regarding population sex ratio.

One aspect of our bioenergetic analysis that remains difficult to resolve is that relative differences in FCE residuals between males and females are greater than would be expected by the male–female differences in bioenergetic residuals of loss terms. Total metabolism, egestion and excretion residuals were all higher in females than in males, after controlling for body size and temperature differences among sexes and lakes, which seems inconsistent with the greater observed growth per unit energy consumed in females. The reason for this apparent discrepancy is not clear however, it suggests further that conventional mercury accumulation or bioenergetics models may be incapable of accurately modelling gender differences, as these models do not reflect potential physiological differences between sexes (e.g. Malison et al. 1985 , 1988 Mandiki et al. 2004 , 2005 ). Gender differences in assimilation could explain some of the discrepancy outlined above if the assimilation of energy (and/or Hg) from diet is higher in males under the influence of hormones associated with the onset of maturity (e.g. Valle et al. 2005 ), then consumption estimates for males would be overestimated. A reduction in male consumption estimates would reduce the observed difference in FCE residuals between male and female perch and help to resolve this apparent discrepancy. Similarly, if standard metabolic rates (i.e. weight exponent of standard metabolism) were higher in males than in females (e.g. Shillington 2005 ), total metabolic costs of males in this study might be underestimated. Another possibility is that females are experiencing compensatory growth as a response to more variable intake relative to males. Fish undergoing compensatory growth due to variable intake have higher growth efficiencies and/or assimilation than those with constant intake ( Skalski et al. 2005 ). Also, bioenergetics models applied to fish exposed to variable intake have underestimated consumption ( Whitledge et al. 1998 ). However, it is not clear why female perch might demonstrate more variable intake patterns than males.

In summary, our study provides a test of two competing hypotheses for the explanation of female-biased SSD in two species of fish, and highlights the importance of measuring both consumption and activity costs in evaluating proximate mechanisms for SSD. Our study and the literature reviewed here suggests that sex-specific bioenergetics models are warranted. Further, we provide a detailed comparison of SSD in yellow perch and walleye, and demonstrate important similarities between these species that transcend the trophic differences that separate them.


References

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Bioenergetics of bioconversions: is there a surplus of energy? - Biology

Dr. Molly Roberts completed her PhD with Dr. Emily Carrington in 2019 in the Biology Department at UW. Her research involved both experimental work at FHL and fieldwork at Penn Cove Shellfish in Coupeville, WA. Prior to her time in graduate school she was a technician in the FHL Ocean Acidification Environmental Laboratory. She is now working with Dr. Sarah Gilman to predict barnacle growth at a field site at Friday Harbor using an energetics framework.

Mussels are bivalve mollusks that live in a wave-swept environment, and the ability to strongly anchor to the habitat is key to their survival. Mussels attach to surfaces by producing a network of protein-based fibers called byssal threads (Figure 1). I was interested in the cost of producing these threads, and the effect of food availability and energetics on their production. I worked with two species, Mytilus trossulus and Mytilus galloprovincialis, a native mussel species and an identical-looking cultured mussel species, both of which end up in stores and restaurants in Washington. Fig. 1: Mussels anchor themselves to their habitat by producing a network of collagen-like fibers known as byssal threads. Credit: E. Carrington.

The question that remained was: what does this loss of growth tell us about the energetic cost of producing byssal threads? I calculated the cost of thread production with a bioenergetics model using information about how much energy it takes to grow new tissue, and the relationship between growth and the number of threads made (Scope for Growth). I found that for mussels in the control group, about 10% of the energy budget was spent on byssal thread production, but that this ranged up to 50% of the energy budget for mussels whose byssal threads were severed daily. In other words, mussels being "forced" to make new threads frequently had much less energy available for growth.

Finally, I was interested in whether these ideas also held in a mussel aquaculture setting. I worked with Penn Cove Shellfish in Coupeville, WA. At this farm mussels are grown on ropes that hang vertically in the water (Figure 3). The seawater conditions at the farm provided a "natural experiment" to test whether mussels that have greater resources­ – given food availability and seawater temperature­ – produced a greater number of byssal threads. Would fluctuations in temperature and food availability over time end up affecting byssal thread production or growth? To answer this question, I used published relationships between temperature, feeding rate and respiration to calculate mussel energy surplus under different conditions, and measured growth and byssal thread production. I found that the calculated energy surplus did correlate with mussel growth over the two-year period, but this value was not a predictor of the quantity of byssal threads produced by mussels at the farm. Instead, mussels experiencing longer periods of low oxygen and acidic water produced fewer byssal threads.


Paper on the origin of life (abiogenesis) shows bioenergetic properties of living cells came from nothing more than rocks, water, and carbon dioxide

The author of the paper, Nick Lane, has written some great popular books on evolution. My favorite one was "Power, Sex, Suicide: Mitochondria and the Meaning of Life." A little bit of a hyped up title but overall a great description of how mitochondria most likely developed with eukaryotic cells and the impact that's had. I would highly recommend his books to anyone who's interested in these subjects.

I agree, that is a great book.

Ok, so the core argument in this paper seems to be that a) a common feature of life as we know it is the harnessing of energy in the form of ion gradients across membranes and b) these gradients can be shown to form naturally from otherwise inert materials in situations like undersea vents, therefore demonstrating that life as we know it is a kind of byproduct of energy. Am I getting that right? Any science ppl able to comment? Extremely succinct and provable origin of life hypothesis.

Yep - that's a perfect TLDR. Lets hope it's provable! Nick Lane actually has a ɻio-reactor' running in the basement of my university labs trying to test just that.

I'm not exactly a 'science person' but overall yes. However, use of ion gradients is a well established fact and has been essential to biochemistry for a long time, however the bigger question was exactly how the use of gradients came into being, which is proposed in this paper. The fact that these gradients are so complicated nowadays is what raised a lot of questions. They have essentially drawn out, "step-by-step" how these gradients could have come into being, likely derived from the non-living chemical gradients in rocks in sea floor vents. Later on, the use of a membrane transporter, a protein, that sends protons one way and sodium the other was one of the first steps in changing from simpler, proton gradients (present in lots of non-living things), to more complex, chemical gradients (like sodium ions and, later on, even more complicated transmitters).

I believe the biggest point of their paper is actually that changing from a proton pump in protocells to a sodium pump appears to be both energetically neutral (in terms of costs), and possible with the genes and proteins present.

The use of ion gradients over membranes for energy con- servation, as in chemiosmotic coupling, is as universal as the genetic code itself, yet its origins are obscure. Insofar as phylogenetics can give any indication of the deepest branches of a ‘‘tree of life,’’ autotrophic, chemiosmotic cells invariably cluster at its base (Say and Fuchs, 2010 Stetter, 2006 Maden, 1995). Although there is little doubt that the last universal common ancestor (LUCA) was chemiosmotic with a mem- brane-bound ATP synthase (Mulkidjanian et al., 2007), how proton and sodium pumping across membranes arose has rarely been addressed. The issue harbors several severe evolutionary problems, but important clues to the early evolution of energy conservation are emerging from biochemical studies of metha- nogens and acetogens that live from the reduction of CO2, using electrons from H2 (Fuchs, 2011 Kaster et al., 2011 Buckel and Thauer, 2012).

I believe that the second law of physics is that all things left alone deteriorate, or something to that effect. So for this to happen, what outside force operated on it to make it do the opposite?

EDIT: Please don't downvote the parent comment. He's asking a legitimate question that deserves an answer.

The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems spontaneously evolve towards thermodynamic equilibrium -- the state of maximum entropy.

The key phrase to note in relation to your question is "isolated system." The earth is not an isolated system. As someone else noted, the earth receives energy from its sun.

It is important to note that the earth is not an isolated system: it receives energy from the sun, and radiates energy back into space. The second law doesn't claim that the entropy of any part of a system increases: if it did, ice would never form and vapor would never condense, since both of those processes involve a decrease of entropy. Rather, the second law says that the total entropy of the whole system must increase. Any decrease of entropy (like the water freezing into ice cubes in your freezer) must be compensated by an increase in entropy elsewhere (the heat released into your kitchen by the refrigerator).


Gas Biological Conversions: The Potential of Syngas and Carbon Dioxide as Production Platforms

Contemporary challenges in decreasing Green House Gas emissions and finding alternative carbon and energy sources for fueling our society brought in the forefront processes based on biological conversions of gaseous substrates, such as syngas and carbon dioxide. Generation of synthesis gas or syngas (a gaseous mixture mainly of CO, H2 and CO2 generated during thermal decomposition of carbonaceous material in the presence of limited amount of an oxidizing agent) is known since the beginning of the 17th century and discovery of Fischer–Tropsch synthetic route in the beginning of the 20th century allowed the development of various routes for chemical catalytic synthesis of fuels and chemicals from syngas. Biological processing of syngas came in the forefront much later, following important advances within Microbiology and Biochemistry disciplines. This thermo-biochemical route for production of low-value products like fuels is considered competitive and advantageous compared to the thermochemical route when small-scale installations are concerned. Production of higher value products via the carboxylate platform is also a promising, and certainly worth-investigating route. Biological conversion of syngas and valorization of CO2 via biological means, besides contributing in greening our world, come with similar product portfolio and share the same technological challenges. Therefore, the target of the current study is to provide an overview of the latest scientific advances within syngas and CO2 valorization to fuels and chemicals and industrial applications and propose a way forward taking into account contemporary challenges and needs.

Graphical Abstract

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Watch the video: Lec 19: Biomass residues and energy conversion routes (January 2022).