Enzymes are proteins that speed up reactions without being used up. A substrate fits an enzyme’s active site. The specific shape explains why an enzyme catalyses a particular reaction. The lock-and-key model is a useful simplification.
As temperature rises towards the optimum, particles move faster and successful collisions increase. Above the optimum, high temperature changes the active site’s shape: the enzyme is denatured. Low temperature slows activity; it does not normally denature the enzyme.
Changing pH away from the optimum reduces activity and may denature the enzyme. Different enzymes have different optima: stomach protease works well in acidic conditions.
| Enzyme | Breaks down | Products | Made in |
|---|---|---|---|
| Amylase (a carbohydrase) | Starch | Sugars | Salivary glands, pancreas, small intestine |
| Proteases | Proteins | Amino acids | Stomach, pancreas, small intestine |
| Lipases | Lipids (fats) | Fatty acids and glycerol | Pancreas, small intestine |
Bile is not an enzyme. It is made in the liver, stored in the gall bladder and released into the small intestine. It is alkaline, so it neutralises stomach acid. It also emulsifies fat into smaller droplets, increasing surface area for lipase.
Specific active sites; optimum temperature and pH; amylase, proteases and lipases.
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