Biology Immunity PMDC Conceptual Practice
PMDC Verified Question 43 of 99
Which distinct structural domain of an antibody molecule determines its unique antigen-binding specificity?
A
Constant region
B
Variable region
C
Fc region
D
Disulfide hinge region
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Variable region
Concept: Immunoglobulin primary structure and Fab domain.

Solution: The variable region (located at the amino-terminal ends of both light and heavy chains) exhibits hypervariable amino acid sequences that form a 3D antigen-binding site (paratope) tailored to a specific epitope.

Why other options are incorrect:
  • Option A & Option C: The constant (Fc) region determines the effector function class (e.g., complement activation, cell receptor binding) and does not bind antigens.

  • Option D: The hinge region provides flexibility to the two Fab arms.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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