Question

How many hypervariable loops are present in (a) IgG and (b) IgM?

Short answer

The number of hypervariable loops in (a) IgG is 12, and (b) IgM is 60.

Step-by-step solution

Structure of an immunoglobulin (Ig)

Immunoglobulins contain at least four subunits: two heavy chains and two light chains. Each of these chains contains one variable region.Threehypervariable loopsreside in every variable domain.

Thus, each chain will have three hypervariable loops. Hence, the total number of hypervariable loops in the four subunits or chains will be = 3 x 4 = 12.

Number of hypervariable loops present in (a) IgG

The IgG is the most common immunoglobulin molecule, which exists as a monomeric structure. Thus, one IgG molecule will have four subunits (two heavy chains and two light chains). Hence, the number of hypervariable loops will be 12.

Number of hypervariable loops present in (b) IgM

The IgM molecules are mostly pentamers; each monomer consists of two heavy chains and two light chains. Now, each monomer contains 12 hypervariable loops. Hence, one IgM molecule's total number of hypervariable loops will be = 5 x 12 = 60.