TPR Amplifire Biochemistry ?

[sshah92]

Hey all,

A little confused about a question I'm working on to review before my test. This is from the amplifire series from TPR.

"Arsenite inhibits the pyruvate dehydrogenase complex. What would be true of a patient exposed to high levels of arsenite?

A) Expired carbon dioxide will decrease substantially
B) Arsenite exerts its effect primarily in the cytoplasm
C) The second complex of the electron transport chain would persist in reduced form
D) Activity of the Krebs Cycle will increase to compensate

So I would think that the answer would be D. My reasoning being that as less pyruvate is converted to acetyl-coA, more fatty acids are used up in place of sugars and therefore the Krebs Cycle picks up. However, the answer is A. I don't really understand why this could be true, especially with the key word "substantially" used. Two CO2s are expired in Krebs whereas just one is released from PDC. So if Krebs continues and PDC is blocked, there isn't that much of a decrease right?

Thanks in advance!

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[horcruxxx]

Probably because PDC also inhibits further Krebs Cycle activity, therefore preventing a lot more CO2 from being expired?

 

[Warrenc]

Pyruvate dehydrogenase is the enzyme that converts pyruvate into acetyl-coa by decarboxylation, giving off CO2.
If you inhibit this enzyme, you don't have any pyruvate converting into acetyl-coa. So if you have high levels of the arsenite (inhibition), you don't undergo the reaction and produce CO2, so A is correct.

I think maybe you're trying to over-complicate the question. I'm sure there is a way for fatty acids to be shunted to the Kreb's cycle instead of glycolysis, but I think the question just wants to see if you know what pyruvate dehydrogenase does and what happens if you inhibit it.
Just my interpretation.