on this cheat sheet
Everything on the GCSE Biology Enzymes poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
What Enzymes Do
Enzymes are proteins that act as biological catalysts. They speed up chemical reactions without being used up. Every chemical reaction in your body is controlled by an enzyme.
Lock and key
Each enzyme has a uniquely shaped active site.
- Only one specific substrate fits, like a key in a lock.
- The substrate binds, the reaction happens, and the products leave.
- The enzyme is unchanged and ready to work again.
Denaturation
Once denatured, an enzyme cannot be fixed. The active site has lost its shape and will not bind the substrate again.
- A normal enzyme has an active site that fits the substrate.
- A denatured enzyme has a deformed active site that will not bind.
Factors Affecting Rate
Temperature
- The rate rises with temperature up to an optimum (about 37°C in human bodies).
- Above the optimum, the rate falls sharply as the enzyme denatures – heat changes the active site shape so the substrate no longer fits.
pH
- Each enzyme has an optimum pH.
- Too acidic or too alkaline denatures the active site.
- Pepsin in the stomach works best at pH 2; amylase in the mouth works best at pH 7.
Substrate concentration
- The rate rises with more substrate, then plateaus once all active sites are full.
- Adding more substrate after that point makes no difference.
Where Enzymes Work
Digestion
Carbohydrase, protease and lipase break down food.
Respiration
Enzymes release energy from glucose.
Photosynthesis
Enzymes build glucose from CO₂ and water.
DNA replication
Enzymes copy DNA before cell division.