Notes
Enzymes are proteins that act as catalysts: they speed up chemical reactions without being used up.
- Enzymes lower the activation energy, the energy needed to start a reaction.
- The molecule an enzyme acts on is its substrate. It binds at the active site.
- Each enzyme is specific to its substrate, like a lock and key.
- Enzymes work best at an optimal temperature and pH. Extreme heat or pH can denature an enzyme by changing its shape.
- Enzyme names often end in -ase (lactase breaks down lactose).
Practice
How do enzymes speed up reactions?
Enzymes make it easier to start a reaction by lowering the energy barrier.
A student measures an enzyme's activity at 20°C, 37°C, 60°C and 80°C. Activity is highest at 37°C and nearly zero at 80°C. Best explanation?
Heat breaks the bonds holding the enzyme's shape, so the substrate no longer fits.
The enzyme lactase breaks down lactose but not sucrose. This shows that enzymes are:
Only substrates that fit the active site are acted on.
Ready for more? Take the Unit 1 test.