Final answer:
Each Fab region on an antibody contains 3 CDRs and 3 HVs, responsible for the specific recognition and binding to antigens.
Step-by-step explanation:
For a single Fab on an antibody, there are 3 CDRs (Complementarity-Determining Regions) and 3 HVs (Hypervariable regions) present. The correct answer is d. 3 ; 3.
The two 'arms' of the Y-shaped antibody molecule are known as the Fab region, which stands for "fragment of antigen binding." Within each Fab region, the light and heavy chains each contain a variable domain that has the antigen-binding site. These domains consist of hypervariable regions, also known as complementarity-determining regions (CDRs), which are crucial for the specific recognition of antigens. There are three CDRs on the light chain and three on the heavy chain, totaling six per Fab.
However, because the question likely refers to each arm individually, each Fab contains three CDRs. The epitope specificity of each Fab region allows for the antibody to bind specifically to an antigen, a crucial part of the immune response.