Toxicology: biochemical effects of lead: practice question

A Forensic Medicine 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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Forensic Medicine · Toxicology: biochemical effects of lead

Sample item

A battery-factory worker has anaemia and abdominal colic, and the blood film shows coarse basophilic stippling of red cells. Which enzymes are inhibited by the metal responsible?

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

The answer and the reasoning

A. ALA dehydratase and ferrochelatase

Lead inhibits delta-aminolevulinic acid dehydratase and ferrochelatase, interfering with haem synthesis. This causes anaemia, basophilic stippling from the inhibition of pyrimidine 5'-nucleotidase, and the excretion of ALA and coproporphyrin in urine. Cyanide inhibits cytochrome oxidase, arsenic inhibits pyruvate dehydrogenase, and organophosphates inhibit cholinesterase.

Option by option

  • A. ALA dehydratase and ferrochelatase (correct)

    Correct. Blocking haem synthesis explains the anaemia and urinary ALA.

  • B. Cytochrome oxidase

    Cytochrome oxidase is inhibited by cyanide.

  • C. Pyruvate dehydrogenase

    Pyruvate dehydrogenase is inhibited by arsenic.

  • D. Acetylcholinesterase

    Acetylcholinesterase is inhibited by organophosphate and carbamate compounds.

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 Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is A, ALA dehydratase and ferrochelatase. Lead inhibits delta-aminolevulinic acid dehydratase and ferrochelatase, interfering with haem synthesis.

Why is "Cytochrome oxidase" not the answer?

Cytochrome oxidase is inhibited by cyanide.

Why is "Pyruvate dehydrogenase" not the answer?

Pyruvate dehydrogenase is inhibited by arsenic.

Why is "Acetylcholinesterase" not the answer?

Acetylcholinesterase is inhibited by organophosphate and carbamate compounds.

What concept does this question test?

It tests Toxicology: biochemical effects of lead in Forensic Medicine. This causes anaemia, basophilic stippling from the inhibition of pyrimidine 5'-nucleotidase, and the excretion of ALA and coproporphyrin in urine. Cyanide inhibits cytochrome oxidase, arsenic inhibits pyruvate dehydrogenase, and organophosphates inhibit cholinesterase.

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 Toxicology: biochemical effects of lead?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine 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.