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 in living organisms 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 into a lock. When the substrate binds, the reaction happens and the products are released. The enzyme is unchanged and ready to work again.
Denaturation
If conditions change too much, the active site loses its shape and the substrate can no longer bind. Once an enzyme is denatured, it cannot be fixed.
Factors affecting rate
- Temperature - rate rises with temperature up to an optimum (around 37 °C for human enzymes), then falls sharply as the enzyme denatures.
- pH - every enzyme has an optimum pH. Pepsin in the stomach works best at pH 2; amylase in the mouth works best at pH 7. Outside the optimum the active site denatures.
- Substrate concentration - rate rises with more substrate, then plateaus once every active site is full. Adding more substrate beyond this point makes no difference.
Where enzymes work
- Digestion - carbohydrase breaks down carbohydrates, protease breaks down proteins, lipase breaks down fats.
- Respiration - enzymes release energy from glucose.
- Photosynthesis - enzymes build glucose from carbon dioxide and water.
- DNA replication - enzymes copy DNA before cell division.