Question

The $\alpha $ - amino acid which contain the aromatic side chain is:
This question has multiple correct options:
A.proline
B.tyrosine
C.valine
D.tryptophan

Answer 1

Hint: In this question, we have to identify which of the $\alpha $ - amino acids contains aromatic side chains. Amino acids are the organic acids having an amino group $\left( { - N{H_2}} \right)$ attached to the carbon chain. Amino groups can be present anywhere in the chain. The amino acids which are derived from proteins contain amino groups on the alpha carbon atom.

Complete step by step answer:
Now we will discuss the given options one by one.
First option is proline. Proline is an essential amino acid but it is not aromatic. It contains a pyrrolidine ring and an acid group is present. The body conditions convert it into a carboxylate ion and are thereby basic.
Second option is tyrosine. Tyrosine is also known as 4-hydroxyphenylalanine and hence in aniline ring there is a phenyl ring which is aromatic in nature. It is obtained from high protein foods like chicken, fish etc.
Third option is valine. Valine is an $\alpha $ - amino acid but is not aromatic. It contains an amino group, a carboxylic group and a side chain of isopropyl group.
Fourth option is tryptophan. Tryptophan is an $\alpha $ - amino acid which is aromatic in nature and used in the biosynthesis of proteins. It contains an amino group, a carboxylic acid group and a side chain indole making it a nonpolar aromatic $\alpha $ - amino acid.
After discussing it we can conclude that tyrosine and tryptophan are the $\alpha $ - amino acids containing an aromatic side chain.
Thus, the correct option is (B) and (D).

Note:
It is found that twenty $\alpha $ - amino acids are the building blocks of peptides and proteins. Ten out of twenty amino acids cannot be synthesized by mammalian tissues through biochemical pathways from the available material in diet. Thus, these amino acids are supplied as such in the diet for proper growth and such amino acids are called Essential or Indispensable amino acids.