IGCSE Biology glossary
Substrate
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Definition
The molecule on which an enzyme acts. The substrate binds to the enzyme's active site, where it is converted into products. Each enzyme is specific to its substrate.
What to include in an exam answer
In lock-and-key questions, say the substrate has a 'complementary shape' to the active site. Never say 'the same shape' as the active site.
Example in context
Explain enzyme specificity using the lock-and-key hypothesis (3 marks): Each enzyme has a specifically shaped active site. Only a substrate with a complementary shape can fit into the active site, like a key fitting a lock. Other substrates cannot bind because their shape is not complementary.
Related syllabus topic
Enzymes