Lock and Key Model in Enzyme Action

Steps:

• Identify the lock and key model: enzymes bind substrates specifically like a lock and key.
• Locate the active site: it forms on the enzyme's surface for substrate binding.
• Assign roles: enzyme functions as the lock, substrate as the key.
• Match to question: active site on enzyme, lock on enzyme, key on substrate.

Why A is correct:

• In the lock and key model, the active site is on the enzyme (the lock), while the substrate is the key that fits precisely, ensuring specificity.

Why the others are wrong:

• B: Incorrectly places active site on substrate instead of enzyme.
• C: Wrongly locates active site on substrate, reversing the model.
• D: Erroneously puts active site and lock on substrate, not enzyme.

Final answer: A