Antibody Structure and Binding Specificity

Steps:

• Identify key antibody regions: variable (V) for antigen binding, hinge for flexibility, constant (Fc) for effector functions.
• Match labels to functions: V at antigen-binding tips, U as hinge region, X and W in constant areas.
• Evaluate choices: A involves flexibility (U), B specificity (V), C/D phagocyte binding (likely Fc as X).
• Confirm B: V's unique sequence ensures specific antigen recognition.

Why B is correct:

• The variable region (V) contains hypervariable loops that form a unique binding site for one specific antigen, per immunological specificity principle.

Why the others are wrong:

• A: Flexibility comes from the hinge (U) alone, not U and X (X is Fc, rigid).
• C: W is likely a constant region without phagocyte receptor binding.
• D: X may be part of Fab or non-Fc, not the phagocyte-binding Fc region.

Final answer: B