Enzyme
Exam-ready definition
A protein that functions as a biological catalyst. It speeds up a chemical reaction without being changed or used up by the reaction.
How this is marked
Both halves are needed for full marks: 'protein' and 'catalyst'. Questions then test the lock-and-key model: substrate shape is complementary to the active site (never say 'same shape as the active site'. Complementary is the paying word).
In an exam answer
Asked what an enzyme does to a reaction: 'The enzyme acts as a biological catalyst, lowering the energy needed so the reaction speeds up, without the enzyme being used up.'
Full topic guide: Enzymes
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