Observe the diagram and answer the following question.

The parts 'P' and 'Q' of the molecule are held by.

Disulphide bonds

The correct answer is Option (4) –Disulphide bonds

Antibodies, also known as immunoglobulins, are protein molecules produced by B-cells as part of the immune response. Each antibody consists of several polypeptide chains. The structure of an antibody includes two types of chains: light chains and heavy chains.

Antibodies have four polypeptide chains in total. There are two small chains called light chains. The small chains are referred to as light chains.  Antibodies have two longer chains called heavy chains. The longer chains are referred to as heavy chains.  The antibody structure is represented as H₂L₂, indicating two heavy chains and two light chains.

The two heavy chains are linked to each other by disulfide bonds and each heavy chain is linked to a light chain by a disulfide bond.