GI physiology: protein absorption: practice question

A Physiology 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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Physiology · GI physiology: protein absorption

Sample item

An 8-year-old child has a photosensitive pellagra-like rash and intermittent ataxia. Urine shows a large excess of neutral amino acids, yet plasma amino acid levels and growth are near normal. Which mechanism explains the preserved nutrition?

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

The answer and the reasoning

D. Dipeptides and tripeptides are absorbed by the PepT1 transporter, bypassing the defective neutral amino acid carrier

In Hartnup disease the neutral amino acid transporter of the small intestine and proximal tubule is defective, so tryptophan is lost and nicotinamide synthesis falls, causing pellagra-like features. Most protein is absorbed as di- and tripeptides through the H+-coupled PepT1 carrier, so overall amino acid nutrition is largely maintained. Nicotinamide and a high-protein diet are used for treatment.

Option by option

  • A. Pancreatic enzymes convert the neutral amino acids into essential amino acids

    Enzymes do not convert one amino acid into another in the lumen.

  • B. Gut bacteria synthesise sufficient tryptophan and nicotinamide from dietary protein

    Bacterial synthesis does not supply enough, as shown by the pellagra-like features.

  • C. Neutral amino acids are absorbed passively by simple diffusion in the colon

    Amino acids are not absorbed by passive diffusion in the colon in significant amounts.

  • D. Dipeptides and tripeptides are absorbed by the PepT1 transporter, bypassing the defective neutral amino acid carrier (correct)

    The PepT1 peptide route bypasses the amino acid transporter defect.

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 Physiology question

What is the answer to this Physiology question?

The best answer is D, Dipeptides and tripeptides are absorbed by the PepT1 transporter, bypassing the defective neutral amino acid carrier. In Hartnup disease the neutral amino acid transporter of the small intestine and proximal tubule is defective, so tryptophan is lost and nicotinamide synthesis falls, causing pellagra-like features.

Why is "Pancreatic enzymes convert the neutral amino acids into essential ami…" not the answer?

Enzymes do not convert one amino acid into another in the lumen.

Why is "Gut bacteria synthesise sufficient tryptophan and nicotinamide from d…" not the answer?

Bacterial synthesis does not supply enough, as shown by the pellagra-like features.

Why is "Neutral amino acids are absorbed passively by simple diffusion in the…" not the answer?

Amino acids are not absorbed by passive diffusion in the colon in significant amounts.

What concept does this question test?

It tests GI physiology: protein absorption in Physiology. Most protein is absorbed as di- and tripeptides through the H+-coupled PepT1 carrier, so overall amino acid nutrition is largely maintained. Nicotinamide and a high-protein diet are used for treatment.

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 GI physiology: protein absorption?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.