Enzymes

Enzymes

What Are Enzymes?

Enzymes are biological catalysts that speed up chemical reactions in the body without being used up. They are made of proteins and have a specific shape that allows them to function.

💡 Key Fact: Without enzymes, many reactions in the body would be too slow to sustain life.

Minimalist enzyme icon with a defined, labelled active site pocket showing a specific complementary shape.

How Do Enzymes Work?

Enzymes work using the lock and key model:

  1. The active site of the enzyme has a specific shape.
  2. The substrate (the molecule the enzyme acts on) fits into the active site like a key in a lock.
  3. The enzyme breaks down or builds up the substrate, forming a product.
  4. The enzyme remains unchanged and can be reused.

💡 Key Terms:

  • Enzyme – A protein that speeds up reactions.
  • Active Site – The part of the enzyme that binds to the substrate.
  • Substrate – The molecule that the enzyme acts on.
  • Product – The result of the reaction.
Three-stage diagram of enzyme action: enzyme and complementary substrate, enzyme–substrate complex at the active site, then the enzyme releasing two product molecules.

Factors Affecting Enzyme Activity

Several conditions affect how well an enzyme works:

Factor

How It Affects Enzyme Activity

Temperature

Too low = slow reaction, too high = enzyme denatures (loses shape).

pH

Too high or too low = enzyme denatures.

Substrate Concentration

More substrate = faster reaction (until enzymes become saturated).

💡 Denaturation: When an enzyme loses its shape, its active site no longer fits the substrate, stopping the reaction.

Examples of Enzymes in the Human Body

Enzyme

Where Found

Substrate

Product

Amylase

Saliva & pancreas

Starch

Maltose (sugar)

Protease

Stomach & pancreas

Proteins

Amino acids

Lipase

Pancreas & small intestine

Lipids (fats)

Glycerol & fatty acids

💡 Bile (made in the liver) neutralises stomach acid and emulsifies fats, helping lipase work efficiently.

Questions 

  1. What is the function of enzymes?
  2. What happens when an enzyme is denatured?
  3. Which enzyme breaks down starch?
  4. How does temperature affect enzyme activity?
  5. What is the role of bile in digestion?

Summary 

  • Enzymes are biological catalysts that speed up reactions without being used up.
  • They work using the lock and key model.
  • Temperature, pH, and substrate concentration affect enzyme activity.
  • Enzymes are essential in digestion (e.g., amylase, protease, and lipase).