17
votes
Accepted
What inactivates pepsin in infants?
EDIT: Thanks a lot to @abukaj for pointing out the mistake in my answer (and to @paracetamol for asking such a beautiful question). I am rewriting my answer to incorporate the (hopefully) correct ...
15
votes
Accepted
Examples of enzymes working in reverse?
Enzymes alter the rate of a reaction by lowering activation energy; they have no effect on the reaction equilibrium ($\ce{K_{eq}}$). Since $\ce{K_{eq}=\frac{k_f}{k_r}}$ and $\ce{K_{eq}}$ is constant, ...
- 17.6k
13
votes
In which direction does ATP synthase rotate?
Short answer
The direction of rotation depends on the viewing point of the observer and the reaction catalyzed by the ATP synthase. When synthesizing ATP, and viewed 'from the bottom' (observer faces ...
- 51.8k
13
votes
Accepted
Can enzymes catalyze thermodynamically unfavorable reactions?
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 ...
12
votes
Can enzymes catalyze thermodynamically unfavorable reactions?
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 ...
- 17.6k
11
votes
Accepted
Can any enzyme be produced?
No, not all enzymes (or other proteins for that matter) can be obtained in functional form by recombinant expression with today's methods. As you suspect, problems arise when complex post-...
- 5,615
11
votes
Accepted
Origin of the biochemical term, Pi (inorganic phosphate)
This terminology is at least as old as September 1944 when Enzymatic Synthesis of Acetyl Phosphate Journal of Biological Chemistry
155, 55-70 was published by Lipmann, which says:
Inorganic ...
- 726
11
votes
Examples of enzymes working in reverse?
What about the ATP synthase? https://en.wikipedia.org/wiki/ATP_synthase it uses proton flow to generate ATP but it can also burn ATP to generate proton flow.
Like other enzymes, the activity of ...
- 3,068
10
votes
Accepted
Origin of enzyme names
As @Chris commented, when assayed in vitro with a single substrate (which may not even be the physiological one) most enzymes can catalyse a reaction in either direction. And enzymes such as pyruvate ...
- 23.3k
9
votes
Accepted
How do DNA, enzymes, hormones etc. reach their proper cellular locations?
The answer given by Sadegh gives a general correct broad view. But one part of the puzzle is missing, which is molecular recognition.
Molecules bind to each other via physical/chemical interaction ...
- 3,068
7
votes
Accepted
Why is aconitase classified as a lyase?
The mechanism of aconitase classifies it as a lyase, even if (under most physiological conditions), the relative concentrations of substrates results in it catalysing the conversion of citrate to ...
- 9,424
7
votes
Identifying type of inhibitor from $K_m$ and $V_{max}$
I think it is possible to identify the type of inhibition from (initial) velocity vs substrate-concentration curves, but it is difficult. The usual way this is done is by using a linear transformation ...
- 4,658
7
votes
Examples of enzymes working in reverse?
Examples of enzymes working in reverse?
Except three enzymes of Glycolysis (Hexokinase, PFK-I and Pyruvate kinase) all catalyse reversible reactions.
As these enzymes catalyse the backward ...
- 8,784
7
votes
Are all enzymes proteins?
Until the late 1980's all enzymes* were believed to be proteins, and were often defined as protein catalysts, often in textbooks which are often not perfect representations of science. At that point ...
- 13.8k
7
votes
How do DNA, enzymes, hormones etc. reach their proper cellular locations?
It's both simple and complex. The simple answer is Brownian motion. All the particles in the cell do have mobility which is related to their mass. A small particle like a soluble enzyme undergoes ...
- 200
7
votes
Accepted
Why can't humans digest dietary fiber when we can digest starch?
"starches are held together with A bonds, dietary fibers are held together with B bonds, and the enzymes only work to break A bonds for X reason"
What you wrote here is correct. ...
- 15.2k
7
votes
Accepted
What is the function of dihydrofolate reductase in humans?
The poster’s assumption that the sole role of dihydrofolate reductase (DHFR) is to convert folic acid to tetrahydrofolate is incorrect. The enzyme is important in at least two metabolic pathways in ...
- 23.3k
7
votes
Is there a way to refine a low resolution Cryo-EM structure using high resolution partial crystal structures?
You should use the original electron density map, not the atomic coordinates associated with it.
Other than that, what you are describing is fairly routine. Briefly, the high resolution structure is ...
- 3,483
6
votes
Accepted
Why is glycerol kinase absent from adipocytes but present in the liver?
The short answer to this question is given in the Wikipedia article on glycerol kinase:
Adipocytes lack glycerol kinase so they cannot metabolize the glycerol produced during triacyl glycerol ...
- 23.3k
6
votes
Accepted
Identifying type of inhibitor from $K_m$ and $V_{max}$
Competitive inhibitor competes for the active site. Therefore it will interfere with the binding of the substrate thereby increasing the apparent KM.
A strictly non-competitive inhibitor does not ...
- 35.2k
6
votes
Examples of enzymes working in reverse?
You mention nucleases and proteases, but if you turn these processes around and think about the actual nucleic acid or protein synthesis reactions an interesting point emerges:
These synthetic ...
- 23.3k
6
votes
Accepted
How does aminoacyl-tRNA synthetase recognize different tRNAs?
You give the answer in your question:
binding areas that recognize a particular tRNA through unique identity sites at the acceptor stem and/or anticodon loop of the tRNA.
The point is that ...
- 23.3k
6
votes
How is the protease inhibited by lopinavir different in SARS-CoV-2 compared to SARS-CoV?
Is there a difference in the gene encoding for the protease?
This paper by Wu et al. annotates the SARS-CoV-2 genome and compares its divergence from other coronaviruses, which may help answer your ...
- 5,550
5
votes
Why is it often the case that an enzyme is favorable only towards one direction of a reaction and not both directions?
Reactions have their set equilibrium constants, which are determined by the free energy of the reactants involved, and this cannot be changed by catalysts, including enzymes. Let's look at your ...
- 5,615
5
votes
Grapefruits and CYP3A4
In general, xenobiotic biotransformation (i.e. processing the xenobiotics aka drugs - detoxing the body) is accomplished by a limited number of enzymes with broad substrate specificities. In humans, ...
5
votes
Accepted
How can human infants express chymosin with only a pseudogene at their disposal?
TL;DR: Chymosin is similar to pepsin and I couldn't find any evidence of functional/expressed chymosin gene in human genome.
It seems like a common misconception that chymosin is functional in humans....
5
votes
Accepted
Is there a DNA analogue to ribozymes?
Not very common, and not found so far in nature, but they exist and are called deoxyribozymes.
Additional information:
Deoxyribozymes are the equivalent of ribozymes in the DNA world and can ...
- 2,883
5
votes
Accepted
Why does uncompetitive inhibition decrease the Michaelis constant?
First off, the difference between the types of inhibition:
competitive inhibition: The inhibitor only binds to the substrate-free form of the enzyme. (Not necessarily at the active site!)
...
- 1,544
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