The big idea: The shape and chemical properties of the active site make an enzyme specific. Anything that permanently changes that shape denatures the enzyme, and it stops working.
The points to remember
- Specificity: only a substrate whose shape and chemistry match the active site can bind.
- The active site's shape is held by bonds between amino acids across the whole protein.
- High temperature or extreme pH breaks these bonds, so the protein's shape changes.
- Denaturation is a permanent change: the active site no longer fits the substrate, so activity is lost.
Remember it as: Shape gives specificity; lose the shape and the enzyme is denatured.
Real example: pepsin. Pepsin digests proteins in the stomach, where the pH is about 2. In the less acidic small intestine it stops working: the change in pH alters the bonds that hold its active site in shape.
Trap: Never say enzymes are killed. Enzymes are molecules, not living things: they are denatured.
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How it is asked: Expect an explanation of why enzymes are specific, why they denature, or, at HL, a long answer on what changes active sites.
IB-style questionExplain[3 marks]
Explain how denaturation affects the activity of an enzyme.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.