Question

Which \[\alpha - \]amino acid can cross linked peptide chains?
A.Serine
B.Cysteine
C.Protein
D.Carbohydrate

Answer 1

Hint: We have to know that the alpha amino acids are made up with a central carbon atom, labelled calcium and it is bound to a primary amino group and one carboxylic group. Which means, the amino group and carboxylic group are the functional group of amino acids which bind with the central carbon atom and naturally, these occur in the form of proteins and peptides.

Complete answer:
We must have to know that serine is an amino acid which his non- essential to the human body. And this is synthesized by the human body. And this serine is used for the protein biosynthesis. But it is not a cross linked peptide chain of alpha amino acids. Hence, option (A) is incorrect.
Cysteine is an amino acid having the formula \[COOH - CH - C{H_2} - SH\]. And it is mainly used to prepare proteins and used in other metabolic functions. The structure of cysteine can be drawn as,

Here, the cross lined linear peptide chain is present and it is formed by the oxidation of cysteine residues. Hence, option (B) is correct.
Proteins are the building blocks of body tissue and it is an essential nutrient for our body. And it does not contain any cross linked peptide chain. Hence, option (C) is incorrect.
The carbohydrates will supply the energy to our body which contain carbon, hydrogen and oxygen atoms. But, there is no cross linked peptide chain in carbohydrates. Hence, the option (D) is incorrect.

Note:
Among these alpha amino acids, the cross linked alpha amino acids is present in cysteine which is a non- essential amino acid. And cysteine contains sulphur in their structure. And this alpha amino acid acts as nucleophile while participating in an enzymatic reaction. This is very essential for metabolic functions. And the other three alpha amino acids do not contain any cross linked peptide chains.