What does the lock and key concept in enzymes illustrate?

• A. The substrate fits the enzyme's active site like a key fits a lock, showing specificity
• B. The enzyme is reused after the reaction
• C. The substrate changes the enzyme shape
• D. The active site is destroyed after reaction

Answer: (D)

Enzyme specificity is shown by the lock and key idea: the active site has a precise shape that fits only the right substrate. When the substrate binds, it forms an enzyme–substrate complex, aligning chemical groups so the reaction can proceed with lower activation energy. After the reaction, the products are released and the enzyme is free to catalyze more substrate molecules; the enzyme isn’t used up and the active site isn’t destroyed. In reality, some enzymes can shift their shape a little to better fit the substrate (induced fit), but the core message is that a specific substrate fits a specific active site, enabling the reaction to occur efficiently.