Glycolysis: arsenate and ATP yield: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Glycolysis: arsenate and ATP yield

Sample item

Arsenate can substitute for inorganic phosphate at glyceraldehyde-3-phosphate dehydrogenase. The resulting 1-arseno-3-phosphoglycerate hydrolyses spontaneously, so phosphoglycerate kinase is bypassed. What is the net ATP yield from anaerobic glycolysis of one glucose molecule in this situation?

ATwoBMinus twoCZeroDFour

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Zero

Normally glycolysis consumes 2 ATP in the preparatory phase and makes 2 ATP at phosphoglycerate kinase and 2 at pyruvate kinase, a net 2. With arsenate the 2 ATP made at phosphoglycerate kinase are lost, leaving 2 (pyruvate kinase) minus 2 (investment), which equals zero. The pathway proceeds but yields no net energy.

Option by option

A. Two
Two is the normal net yield, which requires the phosphoglycerate kinase step that arsenate bypasses.
B. Minus two
Minus two would require pyruvate kinase to fail as well, which arsenate does not cause.
C. Zero (correct)
Two ATP are used and only the two from pyruvate kinase are made, so net ATP is 0.
D. Four
Four is the gross yield in normal glycolysis and ignores the 2 ATP invested and the lost kinase step.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Zero. Normally glycolysis consumes 2 ATP in the preparatory phase and makes 2 ATP at phosphoglycerate kinase and 2 at pyruvate kinase, a net 2.

Why is "Two" not the answer?

Two is the normal net yield, which requires the phosphoglycerate kinase step that arsenate bypasses.

Why is "Minus two" not the answer?

Minus two would require pyruvate kinase to fail as well, which arsenate does not cause.

Why is "Four" not the answer?

Four is the gross yield in normal glycolysis and ignores the 2 ATP invested and the lost kinase step.

What concept does this question test?

It tests Glycolysis: arsenate and ATP yield in Biochemistry. With arsenate the 2 ATP made at phosphoglycerate kinase are lost, leaving 2 (pyruvate kinase) minus 2 (investment), which equals zero. The pathway proceeds but yields no net energy.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Glycolysis: arsenate and ATP yield?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.