LIFE SCIENCE

Detailed explanation-1: -This toroidal (doughnut-shaped) form is the one in which insulin is stored in the beta cells and secreted into the blood stream. Insulin may also form into dimers (double units). However, the active form is a apparently a single unit (monomer).

Detailed explanation-2: -Hence, insulin is a quaternary structure.

Detailed explanation-3: -Insulin is composed of two peptide chains referred to as the A chain and B chain. A and B chains are linked together by two disulfide bonds, and an additional disulfide is formed within the A chain. In most species, the A chain consists of 21 amino acids and the B chain of 30 amino acids.

Detailed explanation-4: -Protein quaternary structure is the fourth (and highest) classification level of protein structure. Protein quaternary structure refers to the structure of proteins which are themselves composed of two or more smaller protein chains (also referred to as subunits).

Detailed explanation-5: -Primary structure. The simplest level of protein structure, primary structure, is simply the sequence of amino acids in a polypeptide chain. For example, the hormone insulin has two polypeptide chains, A and B, shown in diagram below.