Antibody Structure Statements Evaluation

Steps:

• Examine statement 1: X labels the variable region (Fab), which has a complementary shape to the antigen for binding, not a similar shape.
• Examine statement 2: Y labels the hinge region, a flexible area linking Fab and Fc arms, stabilized by disulfide bonds.
• Examine statement 3: Z labels the Fc region, which functions as a hinge-like connector and binds Fc receptors on B-lymphocytes via non-covalent interactions, not disulfides.
• Select option combining correct statements 2 and 3, excluding incorrect 1.

Why C is correct:

• C pairs statements 2 and 3, aligning with antibody anatomy where the hinge (Y) is disulfide-linked and Fc (Z) engages B-cell receptors per immunology definitions.

Why the others are wrong:

• A includes incorrect statement 1 on shape similarity.
• B includes incorrect statement 1 and misattributes hinge to Z.
• D omits correct statement 3 on Z's receptor role.

Final answer: C