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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 ...
another 'Homo sapien''s user avatar
16 votes
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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, ...
canadianer's user avatar
  • 17.8k
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 ...
AliceD's user avatar
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13 votes
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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 ...
another 'Homo sapien''s user avatar
13 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 ...
canadianer's user avatar
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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 ...
DavePhD's user avatar
  • 756
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 ...
alec_djinn's user avatar
  • 3,108
11 votes

Understanding association kinetics

There is a misunderstanding here that is very common when first learning about chemical kinetics. First you say: if $k_{\rm on}$ and $k_{\rm off}$ are both constant but then: if the velocity is ...
knomologs's user avatar
  • 111
10 votes
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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 ...
David's user avatar
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9 votes
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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 ...
alec_djinn's user avatar
  • 3,108
7 votes
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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 ...
March Ho's user avatar
  • 9,452
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 ...
user338907's user avatar
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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 ...
Tyto alba's user avatar
  • 8,782
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 ...
John's user avatar
  • 14.8k
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 ...
Sadegh Ghasemi's user avatar
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. ...
MattDMo's user avatar
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7 votes
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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 ...
David's user avatar
  • 26.1k
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 ...
timeskull's user avatar
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6 votes
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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 ...
David's user avatar
  • 26.1k
6 votes
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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 ...
WYSIWYG's user avatar
  • 35.6k
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 ...
David's user avatar
  • 26.1k
6 votes
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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 ...
David's user avatar
  • 26.1k
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 ...
Alex Reynolds's user avatar
5 votes
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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!) ...
R.M.'s user avatar
  • 1,554
5 votes
Accepted

Are there enzymes for every given reaction?

This will probably be a difficult question to answer definitively without some hand-waving or redefining the question; I can't imagine proving the negative result that no enzyme is possible for a ...
Bryan Krause's user avatar
  • 46.1k
5 votes

Are there enzymes for every given reaction?

Are there enzymes for every reaction? The short answer is, "No" - there are reactions that occur within the human biology that do not require enzymes. One example of this is the formation of advanced ...
Vance L Albaugh's user avatar
5 votes
Accepted

Betaine HCl stomach pH

Betaine HCl (trimethylglycine) was present in over the counter "stomach acidifiers" but the US FDA says there is no evidence for its efficacy and has banned its use for this indication (source: US FDA)...
Bryan Krause's user avatar
  • 46.1k
5 votes

Definition of Cofactor, Coenzyme and Prosthetic Group

On the wikipedia page (en.wikipedia.org/wiki/Cofactor_(biochemistry)) a coenzyme is defined as a complex organic cofactor, so Cl⁻ doesn't count. Another thing that disqualifies it as a coenzyme is ...
VonBeche's user avatar
  • 1,473

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