Question about pyruvate decarboxylation

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uvaGirL07

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Pyruvate decarboxylation occurs in the mitochondrial matrix, correct?
That's what I thought and that's what my notes are saying, but one of the Kaplan practice exam solutions said that pyruvate decarboxylation occurs in the cytoplasm...................... it's an error, right? Just looking for some confirmation. Thanks! 😀
 
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Montserrat said:
And brought back by popular demand !
-------------------------------------


The alpha ketoglutarate dehydrogenase (AKDC) is responsible for catalyzing the third step in the TCA. It has a thiamine pyrophosphate (TPP) prosthetic group that is non covalently bound to the enzyme as part of the active site. It's vital in the function of the enzyme.

A disease in thiamine deficiency, which can be brought about by diets high in polished white rice (in underdeveloped nations) leads to the development of Beriberi. Which best describes the thiamine deficiency's effect on metabolic events in humans ?

A. Glycolysis would continue anaerobically to uphold ATP levels at normal levels
B. Glycolysis rate would increase
C. Acetyl-CoA would be provided via fatty acid metabolism in order that the Krebs cycle proceed as normal
D. Glucose metabolic rate would decrease, with ATP production increasing.
Click to expand...
Okay let's do this. I'm working on process of elimination here.

I will start with C since people seemed to go with that one first. The question is somewhat misleading since in the general pathway of glycolysis --> TCA --> oxid phosphorylation there is actually a step earlier than the one mentioned which requires TPP. That would be the decarboxylation of pyruvate. And acetyl-CoA would be provided via fatty acid metabolism in order to keep things going. But since a later step in the TCA cycle requires TPP as well, the Krebs cycle would not proceed as normal. The most basic point here is that acetyl-CoA formation occurs before the affected step stated within the problem. So someone reading this problem should realize that a supply of acetyl-CoA (which is part of step 1) won't help if step 3 is gone.

Someone said D next. I can't see why this makes sense. ATP production would not increase if TCA were knocked out.

Next I turn to A. All seems well at first. Yes there would be some anaerobics going on since TCA is all out of whack. But it *certainly* could not uphold ATP at a normal level. If it could, we'd all be out there sprinting for hours without running out of breath.

So now I put my faith in B to bail myself out of this question. I turn to the age-old adage, KISS (keep it simple, stupid). "Glycolysis rate would increase." Would it? Well even if you don't know the details about this stuff, you could guess that it would since you aren't really producing any ATP through TCA. And a shortage of ATP would likely get glycolysis moving faster.


FYI a lack of thiamine results in a build-up of pyruvate, lactate, citrate, and alpha-ketoglutarate.
 
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Streetwolf said:
I will start with C since people seemed to go with that one first. The question is somewhat misleading since in the general pathway of glycolysis --> TCA --> oxid phosphorylation there is actually a step earlier than the one mentioned which requires TPP. That would be the decarboxylation of pyruvate.
Click to expand...

Heh. Misleading you say, good sir ? But pyruvate decarboxlyation is the title of the thread !
 
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Montserrat said:
Heh. Misleading you say, good sir ? But pyruvate decarboxlyation is the title of the thread !
Click to expand...

So am I wrong?

I had it down to B and C but I figured C wouldn't be correct since TCA could not go on just because you have an additional acetyl-CoA source. You'll still get stuck on step 3.

And yes, misleading, since the question itself says nothing about pyruvate decarboxylation. To the reader with a small biochemical background it would seem as though the alpha-ketoglutarate DH reaction is the first one which requires TPP.
 
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Streetwolf said:
So am I wrong?

I had it down to B and C but I figured C wouldn't be correct since TCA could not go on just because you have an additional acetyl-CoA source. You'll still get stuck on step 3.

And yes, misleading, since the question itself says nothing about pyruvate decarboxylation. To the reader with a small biochemical background it would seem as though the alpha-ketoglutarate DH reaction is the first one which requires TPP.
Click to expand...

Perhaps you're right - looking at the two dehydrogenase enzymes, they are structurally similar in their tripartite function. I thought it would have been intuitive for someone answering the question to ask themselves if both were similar enough to further investigate for shared prosthetic groups. My bad - the question was worded poorly.

But yep, the answer is B. I dropped Rose786 a hint when I asked her which step the acetyl CoA was entering and which step was inhibited. The other hint I dropped was think simple, which was what you did when you mentioned KISS.
 
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If I miss a glycolysis question on this test, it will be all your fault Monty. Confuse me will you? 😡 :laugh:

I'm gonna fail.
 
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jigabodo said:
You won't.

See, I got this one wrong too and I had a 24.

Actually, maybe I was just lucky that day.
Click to expand...

A lot of the DAT material goes flying out the other ear after a few weeks. It would probably come back quickly though if you looked it over a bit. You earned your score. Can't really secondguess that.
 
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Sadly I didn't reach my goal... :beat:
But I think maybe my scores (20/20/23) are decent enough for SOME school... haha... I began to panic during the science section because all the questions were so different from the types of questions I saw in my review materials (Kaplan, Destroyer, & Achiever). Maybe it was just my test... I don't know... but there were so many oddball questions that I thought I was failing the sections! I was thinking... oh crap!!!!!!!!!!!... here come the 15s and 16s... somehow I managed 20s... I'm surprised I didn't cry during the test... being the baby that I am... hahaha :laugh:
Oh, well... time to playyyyyyyy!!! :hardy:
 
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uvaGirL07 said:
Sadly I didn't reach my goal... :beat:
But I think maybe my scores (20/20/23) are decent enough for SOME school... haha... I began to panic during the science section because all the questions were so different from the types of questions I saw in my review materials (Kaplan, Destroyer, & Achiever). Maybe it was just my test... I don't know... but there were so many oddball questions that I thought I was failing the sections! I was thinking... oh crap!!!!!!!!!!!... here come the 15s and 16s... somehow I managed 20s... I'm surprised I didn't cry during the test... being the baby that I am... hahaha :laugh:
Oh, well... time to playyyyyyyy!!! :hardy:
Click to expand...

GOOOOOD JOOOOOBBBB!!!!!!!!!!!

Nice score!
 
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uvaGirL07 said:
Sadly I didn't reach my goal... :beat:
But I think maybe my scores (20/20/23) are decent enough for SOME school... haha... I began to panic during the science section because all the questions were so different from the types of questions I saw in my review materials (Kaplan, Destroyer, & Achiever). Maybe it was just my test... I don't know... but there were so many oddball questions that I thought I was failing the sections! I was thinking... oh crap!!!!!!!!!!!... here come the 15s and 16s... somehow I managed 20s... I'm surprised I didn't cry during the test... being the baby that I am... hahaha :laugh:
Oh, well... time to playyyyyyyy!!! :hardy:
Click to expand...

Sweet 👍

What was your goal? 30/30/30? :laugh:

Now you have to give us some dirt: Did Bio seem random? Is GChem heavy with calculations? Please say no.
 
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rose786 said:
Sweet 👍

What was your goal? 30/30/30? :laugh:

Now you have to give us some dirt: Did Bio seem random? Is GChem heavy with calculations? Please say no.
Click to expand...

I was striving for a 22, but my MATH score brought down my average!! I sort of knew the math was going to be hard, but I was disappointed because on Achiever math I was scoring 21-23 and Kaplan math I was scoring 22-24. On the real DAT I got an 18 and I couldn't even finish! 👎

What makes me feel worse is that I'm Asian :laugh: and I was an engineering major... :laugh: I definitely did not expect MATH to be my worst score!! LOL

I probably should make a new thread to talk about what I thought about the DAT, but I like my pyruvate thread. haha

Bio: It threw me off guard. I was anticipating a few odd questions since people talked about how different the DAT was becoming, but I definitely did not expect the majority of them to be weird and not straight forward. That's when I started to panic.

Chem: Definitely harder than Kaplan. I also did not expect this section to be so hard because I'm pretty good at chem. I think maybe there were too many calculation problems and thus I spent way too much time on this section.

Orgo: I think orgo was the easiest, but since I spent so much time on chem, I didn't have much time for orgo. I still managed to finish though since this section was the most straightforward and not twisted at all. I had a lot of reactions = fast and simple. 👍

Math: Sucked. Didn't even finish... 👎

Reading: Not bad at all. There a lot of weird questions though. They will give you two statements and ask which is true/false, or if they're both true/false, etc. I was not expecting those. That threw me off guard as well, but it's not difficult. I think maybe it does take a little more time though because it was like two questions in one. How mean!

PAT: On Kaplan I was ranging 21-23, and I got a 23, so I guess it was pretty similar to Kaplan... maybe a bit easier. But angle ranking was... ugh! hehe There were some angles that looked like they were only one degree different! I don't know how you're supposed to figure those out. I had to stare at the angles until I could convince myself that one was bigger than the other so that I could move on with the test. I hate leaving questions undone (perhaps this was the reason for my downfall in math).

Overall: I was thrown off guard so often I felt like I was taking a completely different test. LOL I wish I could have been more informed about the types of questions I would encounter, but what's done is done. Good luck to everyone else taking the exam! Stay calm and don't freak out like I did. I kept thinking that I should just give up and walk out of the test. I think I'm nuts. Be confident!
 
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Last question for a while.
------------------------

DNP (Dinitrophenol) is a proton uncoupler. It destroys the proton gradient by allowing protons a means to flow back into the mitochondrial matrix where it's concentration is lower. Which of the following is inhibited first ?

1) Pyruvate decarboxylation by the PDC
2) Electron Transport
3) Muscular contraction
4 The Krebs Cycle
 
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😍 your scores....do u mind letting me know what bio materials did u used to study and how long did you study to get those scores??? Thanks
 
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joey2007 said:
😍 your scores....do u mind letting me know what bio materials did u used to study and how long did you study to get those scores??? Thanks
Click to expand...

I used DAT Destroyer, DAT Achiever, and Kaplan online course materials. I haven't taken very many biology courses besides the minimum prerequisites (which I took my first year of college = years ago), so my foundation was pretty weak. I started studying around September, so I guess a little less than four months. I didn't study the entire time though, so I'm not sure how long I really studied. Definitely supplement the biology section with other materials. I should've and I've read other people suggesting to do so, but I was too lazy to listen... haha... so umm, you should not make my mistake... so listen to me! LOL :laugh: There was a lot of stuff on the biology section that I don't think I could've known about with the review materials that I was studying from. I asked my boyfriend if he knew how to answer some of the questions that I couldn't, and he was able to pretty easily. He has taken way more upper-level biology courses, so I guess those help. It's hard to buckle down for some hardcore studying RIGHT after you graduate...... haha 🙄 I'd imagine that you could study all three materials (multiple times) in perhaps two months or less if you have a lot of self control. I generally do, but I'm not applying until the next cycle, so I was not under any sort of time constraints.
 
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Montserrat said:
Last question for a while.
------------------------

DNP (Dinitrophenol) is a proton uncoupler. It destroys the proton gradient by allowing protons a means to flow back into the mitochondrial matrix where it's concentration is lower. Which of the following is inhibited first ?

1) Pyruvate decarboxylation by the PDC
2) Electron Transport
3) Muscular contraction
4 The Krebs Cycle
Click to expand...
Oh make them harder! 🙂
 
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Montserrat said:
Last question for a while.
------------------------

DNP (Dinitrophenol) is a proton uncoupler. It destroys the proton gradient by allowing protons a means to flow back into the mitochondrial matrix where it's concentration is lower. Which of the following is inhibited first ?

1) Pyruvate decarboxylation by the PDC
2) Electron Transport
3) Muscular contraction
4 The Krebs Cycle
Click to expand...

Way too easy... unless it's a trick question? I don't think I'll answer now. 😛
 
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rose786 said:
Way too easy... unless it's a trick question?
Click to expand...

It most definitely is a trick question - the answer is not what it seems to be. For the previous question I put up, thinking simple was key. For this problem, the strategy is a bit different 😀.
 
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Montserrat said:
Last question for a while.
------------------------

DNP (Dinitrophenol) is a proton uncoupler. It destroys the proton gradient by allowing protons a means to flow back into the mitochondrial matrix where it's concentration is lower. Which of the following is inhibited first ?

1) Pyruvate decarboxylation by the PDC
2) Electron Transport
3) Muscular contraction
4 The Krebs Cycle
Click to expand...

It took me about 5 solid minutes of hardcore biochemical thought, and re-reading the question about 4 times before I realized what a go-**** I was.

Seems like that biochem degree is working real hard for me :laugh:
 
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My pleasure.

But still... no one even wagered a guess yet ? Paging Dr. Streetwolf - This thread is coding.
 
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the indecision causes even Worf to frown.

8468a5a1-1.gif
 
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Streetwolf said:
I have my answer. Let someone else shout it out first!
Click to expand...

What is 3) Muscular contraction, Alex?

People are going to want to say 2) Electron Transport but decouplers don't inhibit proton transfer, they just break down the gradient. That doesn't affect electron transport, it affects ATP synthesis without which you can't contract your muscles.
 
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armorshell said:
What is 3) Muscular contraction, Alex?

People are going to want to say 2) Electron Transport but decouplers don't inhibit proton transfer, they just break down the gradient. That doesn't affect electron transport, it affects ATP synthesis without which you can't contract your muscles.
Click to expand...

👍

alex.jpg
 
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Okay, I lied. Seriously though, this is the last question, because I can't think of anything else worth asking that involves the PDC. (Psst. No trick questions - all straight forward. Enjoy ! )
---------------------------------

Patients in shock will often suffer from lactic acidosis due to a deficiency in oxygen.

1) Why does a lack of oxygen lead to lactic acid accumulation, since neither the oxidative decarboxylation of pyruvate nor TCA directly require oxygen ?

2) One treatment for shock is to administer dichloroacetate, which inhibits the kinase associated with the pyruvate dehydrogenase complex. What is teh biochemical rational for this treatment ?
 
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You are right!😀 I wrote to them yesterday about this error and here's what they said -

Thank you for your email, and our apologies for the confusion. The
Electron transport chain occurs on the inner mitochondrial
membrane, not inside the matrix. Pyruvate decarboxylation, meanwhile,
occurs in the mitochondrial matrix. Therefore, (E) is the correct
answer to this question. We apologize for this error and any
inconvenience that it may have caused you. Our developers have been
made aware of this issue so that it can be corrected.

Please let us know if you have any other questions.

Good luck with your studies!

Regards,

Bevin
Kaplan Customer Care Center
www.kaptest.com/service
 
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