Question

A semi-indispensable amino acid for human consumption is
(a) Arginine
(b) Valine
(c) Lysine
(d) Leucine

Answer 1

Hint: Only under some pathological conditions, semi-indispensable amino acids are important. This amino acid is a precursor of three high-energy compounds such as guanidophosphate, phosphoarginine, and creatine found in muscles. This side chain of amino acids is composed of a straight 3-carbon aliphatic chain ending in a group of guanidino.

Complete answer:
Arginine and histidine are semi-indispensable, being slow to form in humans. Pathological conditions like premature babies (not completely developed) these amino acids are needed. It may also happen if it is made non-functional due to mutations in any enzyme involved in a particular amino acid synthetic pathway, therefore, although there is a dedicated pathway within the cells for the amino acid synthesis, affected individuals cannot synthesize it due to the underlying conditions. Such amino acids, whose synthesis in an individual's physiology is impaired by such changes, are known as semi-indispensable.
In animals determined by Hopkins, seven amino acids cannot be synthesized. They are also essential amino acids (lysine, methionine, leucine, isoleucine, valine, phenylalanine, and tryptophan) . In humans, there are eight essential amino acids (additional threonine) in number.
Non-essential amino acids include alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.
So, the correct answer is '(a) Arginine'.
Note: In muscle metabolism, arginine is necessary to maintain the nitrogen balance and aid weight control as it encourages muscle mass increase while reducing body fat. It also participates in the synthesis of DNA. In some conditions, arginine and histidine should be included in the diet.