Question

Which of the following is not an essential amino acid?
A. Alanine
B. Valine
C. Histidine
D. Methionine

Answer 1

Amino acids are organic compounds whose major components are carbon, hydrogen, oxygen, and nitrogen. Amine and carboxyl groups are present as functional groups in all the amino acids with additional characteristic elements in side chains. 20 amino acids appear in the genetic code. Essential amino acids are those that can’t be made inside the body but are required from dietary sources.

Complete answer: Amino acids are organic compounds that are required by the cells for their proper functioning and other metabolic activities. The genetic code of the cells encodes the amino acids. There are only 20 amino acids encoded by the body and are termed as standard or non-essential amino acids. In total there are 500 known natural amino acids. The structure of amino acids consists of a carboxyl group and an amine group with a side chain of R-groups that are specific to each type of amino acid. There are a total of 9 essential amino acids that cannot be made by the body and thus are obtained from outer sources such as diet. The rest of the amino acids are conditionally essential amino acids as they are required as supplements in certain age or diseases.
Let us understand the characteristic properties of each given amino acid to know whether it is essential or non-essential.
-Alanine is an amino acid required for the biosynthesis of proteins. Its structure consists of a carboxyl group, amine group, and methyl group as its characteristic side chain. It can be synthesized metabolically from the codon sequences of the genome and thus it is a non-essential amino acid. Codons that encode alanine are GCA, GCC, GCG, and GCU.
-Valine consists of an amino group, a carboxylic group, and an isopropyl group as its characteristic side chain. It is obtained from diet only as the body cannot make it. It is obtained majorly from dairy products, soy products, legumes, and beans. Valine is required for the renewal of hematopoietic stem cells. Also, it has medical significance in the insulin resistance mechanism.
-Histidine contains an amine group, a carboxylic group, and an imidazole side chain as its characteristic property. Histidine is required from dietary sources which makes it an essential amino acid. It is considered essential for infant growth.
-Methionine is also an essential amino acid. It is required for the health of an individual and also for the generation of new blood vessels. Methionine can be obtained from food like eggs, meat, and fish.
Therefore, option A is the correct answer, i.e., Alanine is a non-essential amino acid.

Note: Amino acids are essential requirements of the body to maintain the metabolic processes, protein production, etc inside the cell. The nine essential amino acids are histidine, valine, methionine, tryptophan, threonine, lysine, leucine, isoleucine, phenylalanine. These should be obtained from dietary sources.