Carbohydrate metabolism: fructose: 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: fructose

Sample item

A 1-year-old develops vomiting, hypoglycaemia and jaundice soon after fruit juice and sucrose are introduced. Reducing substances are present in urine. Which enzyme is deficient?

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

The answer and the reasoning

B. Aldolase B

In hereditary fructose intolerance, aldolase B deficiency causes accumulation of fructose 1-phosphate, which traps phosphate and inhibits glycogenolysis and gluconeogenesis, producing hypoglycaemia and liver injury. Treatment is avoidance of fructose, sucrose and sorbitol.

Option by option

  • A. Glucose-6-phosphatase

    G6Pase deficiency causes von Gierke disease and is not triggered by fruit.

  • B. Aldolase B (correct)

    Correct. Fructose 1-phosphate cannot be cleaved.

  • C. Galactose-1-phosphate uridyltransferase

    A deficiency of this transferase causes galactosaemia, triggered by milk.

  • D. Fructokinase

    Fructokinase deficiency causes benign essential fructosuria without symptoms.

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 B, Aldolase B. In hereditary fructose intolerance, aldolase B deficiency causes accumulation of fructose 1-phosphate, which traps phosphate and inhibits glycogenolysis and gluconeogenesis, producing hypoglycaemia and liver injury.

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

G6Pase deficiency causes von Gierke disease and is not triggered by fruit.

Why is "Galactose-1-phosphate uridyltransferase" not the answer?

A deficiency of this transferase causes galactosaemia, triggered by milk.

Why is "Fructokinase" not the answer?

Fructokinase deficiency causes benign essential fructosuria without symptoms.

What concept does this question test?

It tests Carbohydrate metabolism: fructose in Biochemistry. Treatment is avoidance of fructose, sucrose and sorbitol.

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: fructose?

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.