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18

A coupled biochemical reaction is one where the free energy of a thermodynamically favourable reaction (such as the hydrolysis of ATP) is used to 'drive' a thermodynamically unfavourable one, by coupling or 'mechanistically joining' the two reactions. To put it another way, two (or more) reactions may be combined by an enzyme (for example) such that a ...


14

It's pretty simple. A reaction occurs that releases energy (like ATP losing a phosphate to become ADP + Pi). If this is uncoupled, the energy will merely turn into heat. If it is coupled, then it can be used to fuel some other process. For instance, if you couple the ATP -> ADP reaction to a certain protein, the energy can be used to modify the shape of that ...


9

However, I do not understand. Biological evolution does cause the system (living organisms)'s entropy to decrease. So, by the second law of thermodynamics, the entropy of the universe (in this case Earth), must have overall increased. The universe and the earth are not equatable. Earth is not an isolated system. Life causes entropy of the earth to ...


8

I'm no thermodynamics expert, but Ill have a go at this. The energy comes from the original set up, in which you have created a low entropy state. As the diffusion of water molecules equalises their concentration across the membrane so the entropy of the system will increase. This translates to a negative free energy change. That manifests as potential ...


7

The term "irreversible" means that the reverse reaction occurs so rarely that it is considered negligible. This means that you do not have to consider equilibrium, as you have to for reversible reactions. Instead, you can assume that all of the reactants will eventually become product. As you stated, this is true for reactions that have a very negative ...


6

Since there seems to be several distinct sub-topics in your question, I will answer them one-by-one: 1). There are a variety of mechanisms that allow endothermic animals to maintain thermal homeostasis in a cold environment. The main ones are: a). The shivering response: When the core body temperature of a endotherm drops below a critical value (36.8C in ...


5

The energy used to catalyze the peptidyl transferase reaction is from the breakage of the bond between the amino acid in question, and the aminoacyl-tRNA it's attached to. The two reactions are coupled by the ribosome. The ribosome can then lower the entropy by positioning of the molecules (including water) in the active site as described here. So we have ...


4

The free energy change that you quote for the phosphoglycerate kinase (PGK) forward reaction is, of course, the standard free energy change (ΔG0') for the overall reaction. The standard free energy change is defined for all reactants at a concentration of 1M. Note that this value includes the formation of ATP - the free energy of hydrolysis of 1,3-BPG ...


4

Very basically, what they've done in the paper was incubate different DNA sequences with histone octamers which were then separated on a gel. From this they could measure the ratio between nucleosomal and free DNA, which represents an equilibrium constant. This can then be expressed as a change in free energy ($\Delta G=-RTln(K)$), which is what the table ...


3

Measuring the work done by a biological system seems pretty impossible. Imagine how many different ways one cell of your body uses energy (ATP). You can't really measure all the work done by every cell on a macro scale. Metabolic efficiency has been defined as... "health". That seems just a little ambiguous. That's why we use things like averages to ...


2

From pure biophysical viewpoint the question "Why does water buffer sudden temperature changes?" can be answered in the following way: Water has relatively high specific heat capacity. This is the measure of the energy required to raise the temperature of one kilogram of a substance by one kelvin without a change of state occurring. "Relatively high" ...


2

Here answers a part of your question. Warm blood animal burns more food in the winter, so they can keep their body warm. They are not consuming much more ATP in the winter, just a bit more. Usually they have mechanism to reduce the heat loss, like growing hair. How do you know that you need to drink more water? You should know that you area also sweating ...


2

Chlorophyll is a dye that makes leaves green, it plays a key role in photosynthesis. It is present also in unripe fruits, young peas etc. Maybe I should say chlorophylls, because it is a group of similar chemicals. They get degraded by heat. (No assistence of microbes needed). Bonus: Chlorophyll contains magnesium at the molecule core, which facilitates ...


2

Going by the answer, the key to interpret this question seems to be the absence of kinetic energy. Total Energy (mechanical) = Potential + Kinetic (let's ignore the pressure component as this question does not involve it). So the key to answer this question would be a system where the full energy is represented by the Potential energy. In a contracting ...


2

I think you are right and many examples are ambiguous. Even D) is ambiguous as a molecule is always in motion due to entropy except, perhaps, at absolute zero (0 Kelvin). But normally, it does contain kinetic energy. However, as you already identified the ambiguity, look at the best, or in this case least incorrect answer; The only option without any ...


2

Getting long for a comment I can only comment that evolution does not proceed towards thermodynamic optimum. Adaptation is thermodynamic optimization but evolution is directionless. Otherwise the extant species would not suffer from tradeoffs (which they have even in their usual habitat). Establishment of a self replicating cell may be thermodynamically ...


2

Oxygen in photosynthesis does not come from carbon dioxide. It comes from water and this is the step that actually requires light: Photolysis of water. The proton produced in this process is used to synthesize ATP and NADPH by a chemiosmotic process similar to what happens in mitochondria. These biochemical pathways are also referred to as Light reactions. ...


1

Plants need sugar not only for energy but also for synthesizing essential metabolites and building blocks including cellulose (used in cell wall), glycoproteins and 5-carbon sugars for nucleotides. As already mentioned by canadianer, plants respire by oxidizing sugars. This happens mostly during the night. However photosynthesis also produces ATP and ...


1

You'll find the answer glucose best fits the definition of potential energy, as in it's standard state the glucose has all of it's energy stored in it's bonds (1). Every other answer is some sort of expenditure of energy (ATP in the case of firefly luciferase reaction, see (2)).


1

I would say A or D are acceptable, but A is probably the better answer: firstly, the entropy of the planet system alone is probably not increasing (indeed, it's probably near to constant) and as noted elsewhere, you need to consider a closed system to apply the Second Law, so you need to think about everything that comes to and leaves the Earth. This is the ...


1

The Second Law is one of the most misunderstood and misapplied laws of thermodynamics. It has a scope largely confined to physics, nothing more should be read into it. Simply put, it states that "Heat cannot spontaneously flow from a colder location to a hotter location". (Wikipedia) There is nothing about life that violates that, or creates "negative ...


1

You have to look at the complete reaction including the cofactors. In general, you can drive a chemical reaction into directions which are not favorable by: removing products from the environment (if they are gaseous for example or react further) having a huge excess of substrates (and thus making the back reaction less likely to happen) and by coupling ...


1

Whether a reaction is reversible or irreversible, in the presence or absence of an enzyme, is not related to activation energy. An enzyme lowers activation energy in both directions. A reaction is reversible or irreversible depending on the conditions in which this reaction occurs. If there's a sustained high concentration of substrates, most of the ...


1

The phosphoryl transfer potential is one way to think about the free energy available to do useful work when ATP is hydrolysed. As you can see from the free energy equation below, a positive change in entropy will help to decrease (i.e. make more negative) the free energy change. This is why an endothermic reaction can still occur spontaneously if the ...


1

In a coupled reaction energy required by 1 process is supplied by another process. For example: glucose + phosphate becomes glucose.6.phosphate. This is an endergonic reaction and the energy is supplied to this reaction by another reaction which has to be exergonic reaction i.e. ATP which can become ADP+energy.



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