Question

In polypeptide chain of amino acids the end terms are
(A) Amino and serine
(B) Arginine and carboxy
(C) Glycine and valine
(D) Amino and carboxy

Answer 1

Hint: Amino acids are building blocks of protein which forms protein through polymerisation. An amino acid contains an amino group and carboxylic group on the same carbon atom. Serine, arginine, glycine and valine are examples of different types of amino acids.

Complete Solution :
- Amino acid gets polymerised to form a peptide chain by the linkage of successive amino acids through peptide bonds. Peptide bond \[\text{(-NH-CO-)}\] is formed in between two amino acids by eliminating a water molecule.
- The polarity of a polypeptide chain is due to its different polar terminal groups. In a polypeptide chain one end contains amino group$\text{(-N}{{\text{H}}_{\text{2}}}\text{)}$ which is called N-terminal, while the other end of polypeptide chain contains a carboxyl group$(-COOH)$ which is known as C-terminal of the polypeptide chain.
So, the correct answer is “Option D”.

- Additional information – in protoplasm free amino acid is present as a free zwitterion.
The sequence in which amino acids are arranged in a polypeptide chain of protein is known as primary structure of protein, and a protein has more than 100 amino acids in a polypeptide chain.

Note: Amino acids are known as substituted methane in which one hydrogen atom is substituted by an amino group and another hydrogen atom is substituted by a carboxylic group.
- Each amino acid is amphoteric in nature because it contains one acidic $(-COOH)$ and an alkaline group $\text{(-N}{{\text{H}}_{\text{2}}}\text{)}$.