Carbohydrate metabolism: pyruvate dehydrogenase: 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 · Carbohydrate metabolism: pyruvate dehydrogenase

Sample item

A chronic alcoholic presents with confusion, ophthalmoplegia and lactic acidosis. Which enzyme complex needs the cofactor whose deficiency is responsible, besides alpha-ketoglutarate dehydrogenase?

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

The answer and the reasoning

C. Pyruvate dehydrogenase

Thiamine pyrophosphate is a cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, branched-chain keto acid dehydrogenase and transketolase. In deficiency, pyruvate accumulates and is converted to lactate, producing lactic acidosis with Wernicke encephalopathy.

Option by option

  • A. Lactate dehydrogenase

    Lactate dehydrogenase uses NAD+, derived from niacin.

  • B. Glucose-6-phosphatase

    Glucose-6-phosphatase needs no vitamin cofactor.

  • C. Pyruvate dehydrogenase (correct)

    Correct. Thiamine pyrophosphate is required by the E1 subunit.

  • D. Pyruvate carboxylase

    Pyruvate carboxylase uses biotin.

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.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Pyruvate dehydrogenase. Thiamine pyrophosphate is a cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, branched-chain keto acid dehydrogenase and transketolase.

Why is "Lactate dehydrogenase" not the answer?

Lactate dehydrogenase uses NAD+, derived from niacin.

Why is "Glucose-6-phosphatase" not the answer?

Glucose-6-phosphatase needs no vitamin cofactor.

Why is "Pyruvate carboxylase" not the answer?

Pyruvate carboxylase uses biotin.

What concept does this question test?

It tests Carbohydrate metabolism: pyruvate dehydrogenase in Biochemistry. In deficiency, pyruvate accumulates and is converted to lactate, producing lactic acidosis with Wernicke encephalopathy.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Carbohydrate metabolism: pyruvate dehydrogenase?

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.