Protein Modification Disrupts Enzyme Binding

Steps:

• Amino acid replacement alters the protein's primary structure.
• This change can modify the tertiary structure by affecting folding and side-chain interactions.
• The new shape reduces complementarity to the enzyme's active site, preventing binding.
• In induced fit models, the modified protein fails to trigger conformational changes needed for catalysis.

Why A is correct:

• All three explain resistance via enzyme-substrate specificity: tertiary changes (1) alter shape for non-complementarity (2) and prevent induced fit (3), per lock-and-key and induced fit theories.

Why the others are wrong:

• B: Omits 3, but induced fit failure is a valid mechanism for non-digestion.
• C: Omits 1, but tertiary structure shifts directly result from amino acid substitution.
• D: Ignores 1 and 3, as multiple structural factors contribute to enzyme evasion.

Final answer: A