Question

The two polypeptides of human insulin linked together by
A) Hydrogen bonds
B) Phosphodiester bond
C) Covalent bond
D) Disulphide bridges

Answer 1

Peptide is the sort of an Amide bond as being connected between the Alpha-Carboxyl group of one amino acid to the Alpha amino group of another amino group. And the polypeptide is simply a long chain of amino acids which is connected by the Peptide bonds.

Complete answer:

The synthetic insulin prepared in the laboratory to mimic the natural insulin found in humans is called human insulin.
The amino acids are joined in a peptide bond so that they can perform their functions.
Hydrogen bonds are one of the strongest intermolecular attractions. However, it is weaker in comparison with covalent or ionic bonds. Hydrogen bond is found in the human DNA and thus enables the replication of DNA strands.
Phosphodiester bond is a special type of diester bond in which phosphoric acid along with sugar molecules present in the DNA and RNA backbone links two nucleotides together to form oligonucleotide polymers.
Covalent bonds are basically rigid and planar in structure. It is because of the characteristic of partial double bonds of peptide bonds and for the resonating lone pair of electrons on the amide nitrogen.
Disulfide is a different type of protein bond whose main functions include stabilizing the tertiary and quaternary structures of proteins. Two peptide chains as referred to A and B chains are linked together by two disulfide bonds while the additional disulfide is created within the A Chain.
Hence, we can say that two polypeptides of human insulin are linked together by Disulfide bridges.

Thus the correct answer is option ‘D’

Note: When two amino acids are used to link via a peptide bond, it is called a Dipeptide. Similarly, three amino acids will result in a tripeptide and more than three will make a polypeptide bond. In most of the species, it can be seen that A chain of peptide chains consists of 21 and B chain consists of 30 amino acids.