An IgG molecule is digested with papain. Which fragments are generated, and what functional property does each retain?
- A One F(ab')2 fragment that can cross-link antigen and one Fc fragment
- B Two Fab fragments and one Fc fragment that fixes complement but binds no antigen
- C Two Fab fragments that bind antigen individually and one Fc fragment ✓
- D Two Fab fragments and degraded peptide with no intact Fc
Correct answer: C. Two Fab fragments that bind antigen individually and one Fc fragment
Explanation
Papain cleaves the IgG molecule just proximal to the hinge disulfide bonds, yielding two separate monovalent Fab fragments, each retaining a single antigen binding site, plus one intact Fc fragment carrying complement fixation and Fc receptor binding functions. Pepsin cleaves distal to the hinge, producing one bivalent F(ab')2 fragment capable of antigen cross-linking and a degraded Fc portion.
Reference: Basic Immunology, Abbas, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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