Regulation of Enzyme Activity

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jshyun320

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Which of the following is NOT a type of physiological regulation of enzyme activity?

a) covalent modification
b) changes in rate of enzyme synthesis
c) allosteric activation
d) suicide inhibition
e) competitive inhibition


 
Hmm. Makes sense that its competitive inhibition. Why would a system use competitive inhibition as a form of regulation (i.e. negative or positive feedback).

I wasn't sure of what suicide inhibition was either.
 
I think the answer is 'D'. This is not a type of physiological regulation. Why would you irreversibly inhibit an enzyme?
 
Hmm. Makes sense that its competitive inhibition. Why would a system use competitive inhibition as a form of regulation (i.e. negative or positive feedback).

I wasn't sure of what suicide inhibition was either.

A physiological example of competitive inhibition is the inhibition of succinate dehydrogenase by malonate.
 
Am I the only one that thought it could be B? Changing rate of enzyme synthesis wouldn't have any effect on the activity of enzymes already present (and as far as I know they're not going to get old or degrade or anything...are they?)
 
Am I the only one that thought it could be B? Changing rate of enzyme synthesis wouldn't have any effect on the activity of enzymes already present (and as far as I know they're not going to get old or degrade or anything...are they?)


Regulation of transcription seems like a valid physiological regulatory mechanism of proteins.

Anyone have the correct answer?

I'm leaning towards B, because thats not a regulation of activity

I think OP just threw us a bone and is sitting back smoking a cigar, watching us scramble for an answer. :laugh:
 
Which of the following is NOT a type of physiological regulation of enzyme activity?

a) covalent modification
b) changes in rate of enzyme synthesis
c) allosteric activation
d) suicide inhibition
e) competitive inhibition



D is used by drugs. Everything else is physiological.
 
D is used by drugs. Everything else is physiological.

Agree! Both irreversible and competitive inhibition are theoretical basis of drug development but I can't think of a physiological example of irreversible enzyme inhibition. That's why I also chose 'D'. 😀
 
Regulation of transcription seems like a valid physiological regulatory mechanism of proteins.
Yeah turns out it is. Maybe I'm just forgetting my cell biology, but what happens to active enzymes in a cell? Why are newly synthesized enzymes needed? Do the present enzymes get transported out of the cell/degrade or what?
 
Yeah turns out it is. Maybe I'm just forgetting my cell biology, but what happens to active enzymes in a cell? Why are newly synthesized enzymes needed? Do the present enzymes get transported out of the cell/degrade or what?


Proteins have a finite lifetime. This may range from minutes to days. This differs from one enzyme to another. Some proteins are covalently tagged with ubiquitin for degradation by proteasomes. Hence, it has to be resynthesized when needed. Rapid turnover can be costly to the cell, however, proteins with a short half-life can reach new steady states much faster than those with a long half-life. Therefore, it outweighs the cost of resynthesis.
 
As a biochemistry and molecular biology major, I can confirm the answer is D: suicide inhibitors (like penicillin) are not physiological. And I can think of at least two examples of where all those others are used in the body, too, for good measure, lol. And what are suicide inhibitors: they are compounds that irreversibly bind to the enzyme (probably in the active site) deactivating them. Few catalysis mechanisms use covalent bonds, but they are reversible. These are irreversible bonds that aren't just going to break off.

@gettheleadout

"Yeah turns out it is. Maybe I'm just forgetting my cell biology, but what happens to active enzymes in a cell? Why are newly synthesized enzymes needed? Do the present enzymes get transported out of the cell/degrade or what?"

This might be too much information for the MCAT, but active enzymes are degraded in a normal cell all the time. Yeah, that might sound weird, but protein turnover is pretty common. A fine example of something that degrades proteins is a proteasome...the protein can not be needed any more (say insulin when there is enough insulin already in the cell) or when it has gone bad (it hit a reactive oxygen species or something weird). If you are really low on energy, the body will begin to metabolize proteins, too (as you can imagine, this is not a good thing). My professor told me we don't know exactly what qualifies a protein's age, but sometimes carbohydrates normally found on the protein have fallen off through a hydrolysis and that can tell the proteasome that it is old and needs to be broken down.

Newly synthesized enzymes are needed in new environmental conditions as one example (more true for bacteria than eukaryotes): say a bacterium has been transported into a very cold environment. To increase the fluidity of the membrane to prevent freezing, it will add more cholesterol to its membrane. It can do this by making more of the enzymes used in cholesterol synthesis. Transcriptional regulation is key here. Sometimes, too, when bacteria become endospore, you've got totally new proteins that are needed that are usually not needed.

Transcription and translation are pretty common processes in cells: we need to break down proteins that are old or we need more because they've been secreted or environmental conditions have changed.

To look at some *super* cool examples, check out the trp operon or iron response elements. It's sweet stuff,

~Ibrahim~
 
Regulation of transcription seems like a valid physiological regulatory mechanism of proteins.



I think OP just threw us a bone and is sitting back smoking a cigar, watching us scramble for an answer. :laugh:

How did you know?? 😍 hehehe



Thank you all for your answers... I spent almost half an hour trying to figure it out as all of them seemed correct... Thank you again!!! 🙂
 
Hmm. Makes sense that its competitive inhibition. Why would a system use competitive inhibition as a form of regulation (i.e. negative or positive feedback).

I wasn't sure of what suicide inhibition was either.

Lac operon uses competitive inhibition to regulate itself.
 
Proteins have a finite lifetime. This may range from minutes to days. This differs from one enzyme to another. Some proteins are covalently tagged with ubiquitin for degradation by proteasomes. Hence, it has to be resynthesized when needed. Rapid turnover can be costly to the cell, however, proteins with a short half-life can reach new steady states much faster than those with a long half-life. Therefore, it outweighs the cost of resynthesis.
I recall the use of ubiquitin for degradation of mistranslated proteins, but I've never heard of proteins having finite lifespans or why that might be so.
@gettheleadout

"Yeah turns out it is. Maybe I'm just forgetting my cell biology, but what happens to active enzymes in a cell? Why are newly synthesized enzymes needed? Do the present enzymes get transported out of the cell/degrade or what?"

This might be too much information for the MCAT, but active enzymes are degraded in a normal cell all the time. Yeah, that might sound weird, but protein turnover is pretty common. A fine example of something that degrades proteins is a proteasome...the protein can not be needed any more (say insulin when there is enough insulin already in the cell) or when it has gone bad (it hit a reactive oxygen species or something weird). If you are really low on energy, the body will begin to metabolize proteins, too (as you can imagine, this is not a good thing). My professor told me we don't know exactly what qualifies a protein's age, but sometimes carbohydrates normally found on the protein have fallen off through a hydrolysis and that can tell the proteasome that it is old and needs to be broken down.

Newly synthesized enzymes are needed in new environmental conditions as one example (more true for bacteria than eukaryotes): say a bacterium has been transported into a very cold environment. To increase the fluidity of the membrane to prevent freezing, it will add more cholesterol to its membrane. It can do this by making more of the enzymes used in cholesterol synthesis. Transcriptional regulation is key here. Sometimes, too, when bacteria become endospore, you've got totally new proteins that are needed that are usually not needed.

Transcription and translation are pretty common processes in cells: we need to break down proteins that are old or we need more because they've been secreted or environmental conditions have changed.

To look at some *super* cool examples, check out the trp operon or iron response elements. It's sweet stuff,

~Ibrahim~
As far as the protein degradation goes, that's interesting and makes sense. For the rest of the stuff, I'm definitely familiar with the trp operon and the IRE and role of gene regulation in adapting to environmental conditions, I'd just never thought about gene regulation as a form of enzymatic regulation. Learn something new every day I guess. 🙂 Thanks for sharing!
 
No worries. 🙂

Right..it is a little weird how the question is worded. I think when they wrote "enzyme activity", they maybe didn't mean just the activity of a single enzyme, but also the activity of a pool of enzymes (which is how they really are in the cell) and if you have less in the pool...

If you know about IRE's, you're at about the edge of my biochemistry knowledge, haha. 😀
 
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