Arsenate in EK bio in class exam 1, wrong?

[BilalL]

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I feel that examkracker bio did not represent arsenate correctly in their passage on glycolysis.
EK Bio Lecture 1 exam Passage III

Passage Info:
Glycolysis can be interrupted by poisons that interfere with glycolytic enzyme activity. Arsenate. a derivative of arsenic. is a deadly poison that acts as a substrate for glyceraldehyde 3- phosphate dehydrogenase.

Questions:
18. Which of tbe following would most likely occur inside a cell in the presence of arsenic?
A. The concentration of glyceraldehyde 3-phosphate dehydrogenase would decrease.
B. The concentration of glyceraldehyde 3-phosphate would increase.
C. The concentration of aldolase would increase. D. The concentration of 1.3-bisphosphoglycerate
would increase.

Answer to this one is B. However arsenate mimics phosphate and gets incorporated into glyceraldehyde 3 phosphate to produce 1 arseno 3 phospho glycerate. This molecule quickly hydrolyzes to 3 PG w/o producing ATP. So 2 ATP per glucose is not made.

But glycolysis can continue so it cant be inhibiting the enzyme. And it doesnt interrupt glycolysis, it in fact speeds it up although the glycolysis does not produce any net ATP it still produces everything else.

Another question from the passage:

21. The action of arsenate on glyceraldehyde 3-phosphale dehydrogenase is best describe as:
A. competitive inhibition.
B. noncompetitive inhibiti on.
C. allosteric inhibition .
D. negative feedback.

The answer given is A. But I dont think you can classify this as inhibition.

I think the correct way to describe arsenate is as an "uncoupler" of glycolysis, prevent ATP synthesis.

 

[Catburr]

I feel that examkracker bio did not represent arsenate correctly in their passage on glycolysis.
EK Bio Lecture 1 exam Passage III

Passage Info:
Glycolysis can be interrupted by poisons that interfere with glycolytic enzyme activity. Arsenate. a derivative of arsenic. is a deadly poison that acts as a substrate for glyceraldehyde 3- phosphate dehydrogenase.

Questions:
18. Which of tbe following would most likely occur inside a cell in the presence of arsenic?
A. The concentration of glyceraldehyde 3-phosphate dehydrogenase would decrease.
B. The concentration of glyceraldehyde 3-phosphate would increase.
C. The concentration of aldolase would increase.
D. The concentration of 1.3-bisphosphoglycerate would increase.

Answer to this one is B. However arsenate mimics phosphate and gets incorporated into glyceraldehyde 3 phosphate to produce 1 arseno 3 phospho glycerate. This molecule quickly hydrolyzes to 3 PG w/o producing ATP. So 2 ATP per glucose is not made.

But glycolysis can continue so it cant be inhibiting the enzyme. And it doesnt interrupt glycolysis, it in fact speeds it up although the glycolysis does not produce any net ATP it still produces everything else.

The part I bolded, EK doesn't tell you right? You just knew that on your own, or from an outside source? I definitely didn't know all that on my own, so just wondering.

Anyway, I definitely don't defend the book for not giving you a thorough picture of what's going on, and thus making an iffy question. But still, even if you do know all that, you'd still pick B right? It's the only logical choice, I think. Having some other molecule around, acting as a substrate and competing with the usual substrate for a chance at the enzyme is going to increase your concentration of the original substrate.

Another question from the passage:

21. The action of arsenate on glyceraldehyde 3-phosphale dehydrogenase is best describe as:
A. competitive inhibition.
B. noncompetitive inhibiti on.
C. allosteric inhibition .
D. negative feedback.

The answer given is A. But I dont think you can classify this as inhibition.

I think the correct way to describe arsenate is as an "uncoupler" of glycolysis, prevent ATP synthesis.

Seems like some people describe arsenate's effect on glycolysis as "uncoupling" and some say "competitive inhibition." You can find papers on pubmed for both. I'm no expert on the proper use of either term, but it may be that the terms overlap...for example, something that uncouples a given process may do so in different ways, one being competitive inhibition.

Again, even if I had known all of this before answering this question, I'd still pick A based on the given info, "deadly poison that acts as a substrate."

Good luck with your studying...I think you're the person who bought my books! 🙂

 

[whiteshadodw]

I feel that examkracker bio did not represent arsenate correctly in their passage on glycolysis.
EK Bio Lecture 1 exam Passage III

Passage Info:
Glycolysis can be interrupted by poisons that interfere with glycolytic enzyme activity. Arsenate. a derivative of arsenic. is a deadly poison that acts as a substrate for glyceraldehyde 3- phosphate dehydrogenase.

Questions:
18. Which of tbe following would most likely occur inside a cell in the presence of arsenic?
A. The concentration of glyceraldehyde 3-phosphate dehydrogenase would decrease.
B. The concentration of glyceraldehyde 3-phosphate would increase.
C. The concentration of aldolase would increase. D. The concentration of 1.3-bisphosphoglycerate
would increase.

Answer to this one is B. However arsenate mimics phosphate and gets incorporated into glyceraldehyde 3 phosphate to produce 1 arseno 3 phospho glycerate. This molecule quickly hydrolyzes to 3 PG w/o producing ATP. So 2 ATP per glucose is not made.

But glycolysis can continue so it cant be inhibiting the enzyme. And it doesnt interrupt glycolysis, it in fact speeds it up although the glycolysis does not produce any net ATP it still produces everything else.

Another question from the passage:

21. The action of arsenate on glyceraldehyde 3-phosphale dehydrogenase is best describe as:
A. competitive inhibition.
B. noncompetitive inhibiti on.
C. allosteric inhibition .
D. negative feedback.

The answer given is A. But I dont think you can classify this as inhibition.

I think the correct way to describe arsenate is as an "uncoupler" of glycolysis, prevent ATP synthesis.

G3P dehydrogenase gets inhibited, in fact it shouldn't matter what kind of inhibition is going on here, the enzyme is inhibited and you are told this. enzyme inhibition is almost the same thing as having no enzyme. if you don't have an enzyme, the reaction proceeds slower and you get a build up of substrate/reactant.

arsenate is a substrate for G3P dehydrogenase and therefore mimics the G3P. by definition it makes arsenate a competitive inhibitor.

i think you are thinking too much about these questions. you don't need to bring in a ton of biochemistry background to answer them. i've actually found that the more background knowledge you bring in the worse you'll do. there is maybe 1-2 questions in any chapter exam that requires outside knowledge. even then, sometimes you should get rid of the incorrect answers to find the correct answer.

 

[BilalL]

Catburr, the bolded info is from my biochem course so I guess I should not have thought to much about it.

Thanks for the guidance. I guess I need to forget my outside knowledge while answering questions. It just irked me with arsenate as it was a test question in one of my biochem courses so I got a bit confused after doing the EK passage.

I just started studying so the fact that I should limit the intrusion of my outside knowledge is a bit new to me.

However, I did pick the correct answers but had to slow down and think about them.

And yes Catburr, I did buy your books! Thanks!

 

[Catburr]

Limiting outside knowledge is such a weird thing. There's obviously a lot of questions that require outside knowledge. But then there's questions where you can really lose time by not just reading the answer from the passage.

At least regarding AAMC practice tests and my actual test, I sort of felt like on the questions where outside knowledge was needed, it was a really obvious, concrete fact that I needed to remember. Like, which organic chemistry reagent is stronger, or which atom has a higher ionization energy, or how to apply a formula, etc.

It's something you can get a feel for, to some extent, just by spending time doing practice questions. So don't worry about it, because more than likely you'll naturally train yourself out of overthinking.

 

[whiteshadodw]

Limiting outside knowledge is such a weird thing. There's obviously a lot of questions that require outside knowledge. But then there's questions where you can really lose time by not just reading the answer from the passage.

At least regarding AAMC practice tests and my actual test, I sort of felt like on the questions where outside knowledge was needed, it was a really obvious, concrete fact that I needed to remember. Like, which organic chemistry reagent is stronger, or which atom has a higher ionization energy, or how to apply a formula, etc.

It's something you can get a feel for, to some extent, just by spending time doing practice questions. So don't worry about it, because more than likely you'll naturally train yourself out of overthinking.

yeah, you can get a feel for which questions are:
"outside knowledge"
and which ones are "easy peasy"
and which ones are "ok knowing what you know and given the passage information..."

usually if a question is asking about something and there is info given to you on a passage, don't look over it. for example, you technically could get a passage on a controversial subject, and only 1 view is presented. don't start bringing in random knowledge from a journal article you read a while ago.

also, to get a feel for the concepts that you should know, check out the AAMC outline. you'll see you only need to know the following types of "Control of Enzyme activity":
-feedback inhibition
-competitive inhibition
-noncompetitive inhibition