32

Proteins can move around the membrane. Most proteins do move within the membrane. The membrane is a liquid crystal and has fluid behaviour. Specifically, this is due to the membrane being in a gel-state. This gel state allows phase behaviour which means that the protein is able to move around on the surface. This results in an effect that is often referred ...


28

A reaction where the the free energy of a thermodynamically favorable transformation, such as the hydrolysis of ATP, and a thermodynamically unfavorable one, are mechanistically joined into a new reaction (or may be envisaged to be so joined) is known as a coupled reaction. To put it another way, two or more reactions may be combined mechanistically such ...


13

Enzymes can catalyze a thermodynamically unfavorable reaction by coupling it with a thermodynamically favorable reaction. Most often, enzymes use ATP hydrolysis reaction (energetically favorable) as a source of energy (in simple terms) to drive the unfavorable reaction forward. One important point to keep in mind here is that enzymes don't drive a reaction ...


12

Can enzymes catalyze thermodynamically unfavourable reactions? Enzymes don't change the equilibrium of a reaction, but the fact that an equilibrium exists means that the reaction proceeds in both the forward and reverse directions. Before equilibrium is attained, ΔG for the reaction is not 0. Thus, by definition, one direction is thermodynamically ...


10

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 ...


10

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 ...


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 decrease. ...


9

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 ...


8

In my opinion there might be two reasons why the camel hump (rather than bump) might be one of the adequate adaptations of camels to living in the cold (additional to their flat feet giving hold on both snow and sand and tooth structure, Rybczynski et al., 2012). Both match the humps being fat storages in modern camels. The first is also provided by ...


8

Unless you have a closed system, don't bother with the second law. These sound like some poetic descriptions but they won't tell you much about biology. It is argued that cell senescence is due to the accumulation of defects and wastes, but cell death could have a more active implication of carrying away the debt caused by utilizing information. The ...


7

No other answer has mentioned this so I created an account just to say this. Some membrane proteins do not move. This is because they are fixed in that position in the membrane due to the cytoskeleton. Erythrocytes are a good example of this. The main protein that is immobilised in erythrocyte membrane is Band 4.1 protein, and its immobilised by Spectrin. ...


7

2nd law of thermodynamics states that the overall entropy of the universe cannot decrease at any time. This can also be stated as the fact that the universe naturally falls towards the lowest energy state, or equilibrium. This becomes important in metabolic reactions. Reactions which seem to increase the state of energy, or perhaps the 'order' of the ...


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 ...


6

There are two types of proteins that are present in a membrane, because you have not been specific about which type of protein you are talking about I will consider that you are talking about Integral membrane proteins. For more clarity I will begin by explaining to you what are these proteins present in the membrane. As I said there are two types of ...


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

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 the ...


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

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. ...


3

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 ...


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 ...


3

Summary The first explanation is commonly encountered. The second explanation cannot be correct, as it stands, as it ignores the free energy change in the protein. A modification of the second explanation (perhaps what was intended) is that it is necessary to consider the protein folding and change in the water as being coupled, in which case the overall ...


3

Naturally occurring proteins are evolved such that this is the case Natural proteins only occupy a very small amount of sequence space. For a 200 aa protein, there are $20^{200} \approx 10^{260}$ possible sequences. There are nowhere near that many naturally occurring protein sequences, even if you take into account all the different alleles in the ...


3

You have to consider the full redox reaction to determine if the reaction is favourable or not. It's not correct to think of enoyl-CoA alone as "higher energy" than acyl-CoA, because of the free energy difference $\Delta G$ of the half-reaction: acyl-CoA $\leftrightarrow$ enoyl-CoA + 2 $e^-$ cannot be determined without knowing what the electron acceptor ...


3

You are correct in stating the relative rates of the two reactions. What may have you confused is the percent sign in the statement. The percent sign is not a unit in the sense that you are taking it. What you have in a simple reaction like you are examining are two opposing rates of reaction. The rate of a catalytic reaction, like others, usually ...


3

Most people most of the time live in the environments that have lower temperatures than it is their normal body temperature (36-37 °C). And most people sweat sometimes at these temperatures. In the summer, when it is 30 °C and you wear only swimming trunks, even light walking can make you sweat. The same can occur in the winter when the ambiental ...


3

The equilibrium constant $K$ is the quotient of the rate constants of forward ($k_1$) and backward reactions ($k_{-1}$) (for elementary reactions). E.g., for an equilibrium $$\ce{A + B <=> C + D}$$ we get $$\frac{[C][D]}{[A][B]} = K = \frac{k_1}{k_{-1}}$$ So, If both rate constants are affected in the same way (multiplied by the same speed-up ...


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

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 ...


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