Amino acid metabolism: tyrosine catabolic products: 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 · Amino acid metabolism: tyrosine catabolic products

Sample item

Tyrosine is degraded by transamination, oxidation and ring cleavage. The terminal products of this pathway enter intermediary metabolism, making tyrosine both glucogenic and ketogenic. What are these products?

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

The answer and the reasoning

C. Fumarate and acetoacetate

Fumarylacetoacetate is cleaved by fumarylacetoacetate hydrolase into fumarate, which is glucogenic, and acetoacetate, which is ketogenic. Phenylalanine follows the same route after hydroxylation to tyrosine. A block at the last step causes tyrosinaemia type I.

Option by option

  • A. Succinyl-CoA and acetyl-CoA

    Succinyl-CoA and acetyl-CoA arise in the catabolism of isoleucine, not tyrosine.

  • B. Pyruvate and acetyl-CoA

    Pyruvate and acetyl-CoA arise from tryptophan and threonine.

  • C. Fumarate and acetoacetate (correct)

    Correct. Fumarate (glucogenic) and acetoacetate (ketogenic) are the end products.

  • D. Alpha-ketoglutarate and acetoacetate

    Alpha-ketoglutarate arises from glutamate, histidine and proline, not tyrosine.

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, Fumarate and acetoacetate. Fumarylacetoacetate is cleaved by fumarylacetoacetate hydrolase into fumarate, which is glucogenic, and acetoacetate, which is ketogenic.

Why is "Succinyl-CoA and acetyl-CoA" not the answer?

Succinyl-CoA and acetyl-CoA arise in the catabolism of isoleucine, not tyrosine.

Why is "Pyruvate and acetyl-CoA" not the answer?

Pyruvate and acetyl-CoA arise from tryptophan and threonine.

Why is "Alpha-ketoglutarate and acetoacetate" not the answer?

Alpha-ketoglutarate arises from glutamate, histidine and proline, not tyrosine.

What concept does this question test?

It tests Amino acid metabolism: tyrosine catabolic products in Biochemistry. Phenylalanine follows the same route after hydroxylation to tyrosine. A block at the last step causes tyrosinaemia type I.

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 Amino acid metabolism: tyrosine catabolic products?

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.