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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 ...


12

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 ...


7

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 ...


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 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 ...


3

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 ...


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

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

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" ...


1

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 ...


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

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 ...


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 ...



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