Carbohydrate metabolism: dichloroacetate and lactic acidosis: 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: dichloroacetate and lactic acidosis

Sample item

Dichloroacetate lowers lactate in some cases of congenital lactic acidosis by increasing flux through pyruvate dehydrogenase. Which enzyme does it inhibit?

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

The answer and the reasoning

C. Pyruvate dehydrogenase kinase

Phosphorylation by pyruvate dehydrogenase kinase inactivates the complex. Dichloroacetate inhibits this kinase, so the complex stays dephosphorylated and active, and pyruvate is oxidised instead of being reduced to lactate.

Option by option

  • A. Pyruvate dehydrogenase phosphatase

    The phosphatase activates the complex; inhibiting it would increase lactate, not lower it.

  • B. Lactate dehydrogenase

    Inhibiting lactate dehydrogenase would block pyruvate-lactate interconversion and does not act on the complex.

  • C. Pyruvate dehydrogenase kinase (correct)

    Correct. Inhibiting the kinase keeps the complex in its active, dephosphorylated form.

  • D. Pyruvate carboxylase

    Pyruvate carboxylase converts pyruvate to oxaloacetate and inhibiting it would not enhance pyruvate oxidation.

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 kinase. Phosphorylation by pyruvate dehydrogenase kinase inactivates the complex.

Why is "Pyruvate dehydrogenase phosphatase" not the answer?

The phosphatase activates the complex; inhibiting it would increase lactate, not lower it.

Why is "Lactate dehydrogenase" not the answer?

Inhibiting lactate dehydrogenase would block pyruvate-lactate interconversion and does not act on the complex.

Why is "Pyruvate carboxylase" not the answer?

Pyruvate carboxylase converts pyruvate to oxaloacetate and inhibiting it would not enhance pyruvate oxidation.

What concept does this question test?

It tests Carbohydrate metabolism: dichloroacetate and lactic acidosis in Biochemistry. Dichloroacetate inhibits this kinase, so the complex stays dephosphorylated and active, and pyruvate is oxidised instead of being reduced to lactate.

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: dichloroacetate and lactic acidosis?

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.