Top Score Lactic Acid Fermentation Question

[Meat Gyver]

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What do muscle cells during oxygen deprivation gain from the conversion of pyruvate?

A. ATP and lactate.
B. NAD+ and lactate
C. CO2 and lactate
D. ATP and alcohol
E. ATP, lactate, CO2

Correct answer is B, but couldn't A also be a correct answer too.

They clearly mention in the solution that "ATP, NAD+, and lactate are gained by the muscle cell"...so what makes B better than A.

I'd understand chioce B to be correct if they asked "what products are formed from the conversion of pyruvate in oxygen depleted muscle cells?"

However by saying what do the cells gain, is almost like saying "how do they benefit." Yes NAD+ forms, but it goes into making more ATP, so that is what the cell truly gains.

Haha I'm most likely over analyzing this, but if someone could better explain the answer, I'd appreciate it.

 

[themrn]

What do muscle cells during oxygen deprivation gain from the conversion of pyruvate?

A. ATP and lactate.
B. NAD+ and lactate
C. CO2 and lactate
D. ATP and alcohol
E. ATP, lactate, CO2

Correct answer is B, but couldn't A also be a correct answer too.

They clearly mention in the solution that "ATP, NAD+, and lactate are gained by the muscle cell"...so what makes B better than A.

I'd understand chioce B to be correct if they asked "what products are formed from the conversion of pyruvate in oxygen depleted muscle cells?"

However by saying what do the cells gain, is almost like saying "how do they benefit." Yes NAD+ forms, but it goes into making more ATP, so that is what the cell truly gains.

Haha I'm most likely over analyzing this, but if someone could better explain the answer, I'd appreciate it.

well the point of doing is to regenerate NAD+, since there's no pyruvate for TCA cycle. TCA cycle not only produces ATP (in forms of GTP), NADH, and FADH2, it also regenerates NADH back to NAD+ so it can be used in glycolysis. Since TCA cycle cannot do this job (b/c no pyruvate), it alternates to lactic acid fermentation in the muscle (which don't make any ATP).

Correct me if i'm wrong...

 

[kyeongkong]

What I think is, the question asks the gaining from conversion of "pyruvate". I think that part is important. ATP is generated when glucose is converted to pyruvate (Glycolysis). But pyruvate to lactic acid uses NADH and frees NAD+ as a product. So maybe that is why.

 

[Ogoz]

so if oxygen is absent there are two anaerobic pathways that pyruvate will go. First pathway is the Alcohol fermentation and the products are CO2, ethanol, and NAD+. The second pathway is Latic acid fermentation and the products are NAD+ and Lactate.

ATP are produce during glycolysis, Kreb cycle(aerobic) and Oxidative phosphorylation(aerobic). The key here is which pathway will pyruvate go if oxygen is not present. so therefore, all the answer keys with ATP are incorrect.

 

[Meat Gyver]

The reason the muscle cells switch from aerobic respiration to lactic acid fermentation doesn't deal with the TCA cycle, but rather when the sugar catabolism outpaces the supply of oxygen from the blood. The problem is that there will be a surplus of pyruvate, but no oxygen to accept electrons at the end of the electron transport chain. Through lactic acid fermentation, pyruvate is directly reduced by NADH into lactate, thus liberating NAD+. With the free NAD+, it can continue glycolysis since it doesn't rely on oxygen. The net ATP will be 2, which is much better than 0.

But I'd double-check the TCA cycle being able to convert NADH into NAD+. I'm pretty sure the only time that occurs in aerobic respiration is during oxidative phosphorylation where NADH and FADH2 give up electrons to the electron transport chain.

 

[Meat Gyver]

What I think is, the question asks the gaining from conversion of "pyruvate". I think that part is important. ATP is generated when glucose is converted to pyruvate (Glycolysis). But pyruvate to lactic acid uses NADH and frees NAD+ as a product. So maybe that is why.

Sweet, makes sense to me. I definitely over-thought that one. Thanks!