Nonessential in normal health but essential during conditions of enhanced growth or surgical recovery

Case details

An 8-year-old child requires surgical intervention and substantial recovery time in the hospital. A nutritionist recommends a specific dietary plan. The plan includes a protein rich diet with the special supplementation of an amino acid that is typically considered a nonessential, but becomes an essential amino acid under conditions of enhanced growth or surgical recovery. Which of the following amino acids should be considered in this dietary plan?

A. Alanine

B. Arginine

C. Glycine

D. Serine

E. Tyrosine

The correct answer is Arginine.

Arginine is a semi essential amino acid. It can be synthesized in the human body but during the times of growth, reproduction or recovery from illness, its requirement is increased and under those conditions, an imbalance is set between demand and supply, thus it has to be supplied in the diet, which makes it essential during those conditions.

Arginine is synthesized in the urea cycle, from arginosuccinic acid, by the action of Argino succinic acid lyase enzyme (Figure).The urea cycle operates only in the liver, and thus the synthesis of arginine through this pathway is limiting. The amount of arginine produced through this pathway is sufficient for healthy adults, but it may not be sufficient in times of growth or repair, where increased protein synthesis demands increased supply of amino acids. Thus, in growing children and in adults following surgery, arginine becomes an essential amino acid.

Urea cycle

Figure- Synthesis of Arginine. Enzymes- CPS-1- Carbamoyl synthetase-1, OTC- Ornithine transcarbamoylase, ASS- Argino succinic acid synthetase, ASL- Argino succinic acid lyase and ARG- Arginase.

As regards other options

Glycine is a nonessential amino acid; it can be synthesized in sufficient amounts even at the times of increased requirement. It can be synthesized de novo or from serine.

Similarly serine can be synthesized from Glycine, phosphoglycerate or from hydroxy pyruvate, its production is also not limiting during conditions of increased demand.

Tyrosine can be synthesized from phenyl alanine, but it becomes an essential amino acid in Phenylketonuria, that occurs due to deficiency of phenyl alanine hydroxylase, the enzyme that catalyzes the conversion of phenyl alanine to tyrosine.

Hence the most suited option out of all is arginine.

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1 Response

  1. Anthony Moyi says:

    So what are the dietary sources for Arginine

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