• Structural Architecture of the Antigen-Binding Site (Paratope):
• Immunoglobulin Anatomy:
• An antibody monomer consists of two identical heavy (H) chains and two identical light (L) chains.
• The antigen-combining paratope is formed by the pairing of the variable domain of the heavy chain ($V_H$) and the variable domain of the light chain ($V_L$), located at the N-terminal ends of both heavy and light chains (Fab fragment).
• terminal regions form the constant Fc effector domain.
• Conclusion: N terminal side of heavy and light chain (Option 3).

Correct option: (3) N terminal side of heavy and light chain