Free radicals: superoxide dismutase: 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 · Free radicals: superoxide dismutase

Sample item

A 45-year-old man has progressive limb weakness with both upper and lower motor neuron signs, and a family history of similar illness. Genetic testing finds a mutation in the SOD1 gene. Which reaction is normally catalysed by this enzyme?

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

The answer and the reasoning

A. Dismutation of superoxide to hydrogen peroxide and oxygen

Copper-zinc superoxide dismutase (SOD1) converts two superoxide radicals and two protons to hydrogen peroxide and oxygen. Catalase and glutathione peroxidase then detoxify the peroxide. Dominant SOD1 mutations cause familial amyotrophic lateral sclerosis through a toxic gain of function.

Option by option

  • A. Dismutation of superoxide to hydrogen peroxide and oxygen (correct)

    Correct. SOD dismutates superoxide to hydrogen peroxide.

  • B. Conversion of hydrogen peroxide to water and oxygen

    This is the reaction of catalase.

  • C. Reduction of hydrogen peroxide using reduced glutathione

    This is the reaction of glutathione peroxidase, a selenoenzyme.

  • D. Reduction of oxygen to superoxide using NADPH

    This is the action of NADPH oxidase in phagocytes, which generates superoxide.

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 A, Dismutation of superoxide to hydrogen peroxide and oxygen. Copper-zinc superoxide dismutase (SOD1) converts two superoxide radicals and two protons to hydrogen peroxide and oxygen.

Why is "Conversion of hydrogen peroxide to water and oxygen" not the answer?

This is the reaction of catalase.

Why is "Reduction of hydrogen peroxide using reduced glutathione" not the answer?

This is the reaction of glutathione peroxidase, a selenoenzyme.

Why is "Reduction of oxygen to superoxide using NADPH" not the answer?

This is the action of NADPH oxidase in phagocytes, which generates superoxide.

What concept does this question test?

It tests Free radicals: superoxide dismutase in Biochemistry. Catalase and glutathione peroxidase then detoxify the peroxide. Dominant SOD1 mutations cause familial amyotrophic lateral sclerosis through a toxic gain of function.

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 Free radicals: superoxide dismutase?

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.