Enzymes- protein molecules made up of chains of amino acids.
- They turn larger molecules into smaller ones
- They do not get used up as they work
- They are specific to a certain type of molecule
- They change shape as they work.
They act as biological catalysts so they can speed up chemical reactions.
Activation energy- the minimum amount of energy particles must have to be able to react.
The reaction is more likely to happen if:
- reacting particles bump into each other
- increase the energy of the particle collisions
- reduce the activation energy needed
How an enzyme works
- Enzymes are made of long chains
of amino acids. The chains are
folded to form the active site.
- The substrate (reactant)
binds to the enzyme to form an
- When the reaction is complete the
products are released and the enzyme
can be used again.
Factors affecting enzyme action
- Enzyme activity is affected by temperature and pH.
- Effect of temperature on enzymes: the rate of enzyme controlled reactions increases with an increase in temperature.
- Substrate particles are more likely to collide with enough energy to react.
- After temperatures of about 40'C, the protein structure of the enzyme is affected by the temperature.
- The long amino acid chains begin to unravel and the shape of the active site changes.
- The enzyme is denatured
- It can no longer act as a catalyst, so the rate of reaction drops dramatically.
- Most human enzymes work best at 37'C
Effect of pH on enzymes: A change in pH affect the forces between the different parts of the protein molecule which hold the folded chains in place.
- If the pH changes, it interferes with the bonds/forces holding the enzyme together, changing the shape of the molecule and denaturing it.
- All enzymes have an optimum pH, eg.
- pepsin: used to break down proteins in the stomach and works best at pH 2.
- amylase: found in the small intestine and works best at pH 8.
- Aerobic respiration involves chemical reactions which use oxygen and sugar and release energy.
- Glucose + oxygen → Carbon dioxide + water (energy)
- Most reactions in aerobic respiration happen inside the mitochondria.