5.1 Enzymes

2026 Syllabus Objectives

  1. Describe a catalyst as a substance that increases the rate of a chemical reaction and is not changed by the reaction
  2. Describe enzymes as proteins that are involved in all metabolic reactions, where they function as biological catalysts
  3. Describe why enzymes are important in all living organisms in terms of a reaction rate necessary to sustain life
  4. Describe enzyme action with reference to the shape of the active site of an enzyme being complementary to its substrate and the formation of products
  5. Investigate and describe the effect of changes in temperature and pH on enzyme activity with reference to optimum temperature and denaturation
  6. Explain enzyme action with reference to: active site, enzyme-substrate complex, substrate and product
  7. Explain the specificity of enzymes in terms of the complementary shape and fit of the active site with the substrate
  8. Explain the effect of changes in temperature on enzyme activity in terms of kinetic energy, shape and fit, frequency of effective collisions and denaturation
  9. Explain the effect of changes in pH on enzyme activity in terms of shape and fit and denaturation

Biological Catalysts 🔬

https://cambridgeassistant.com

What are Catalysts?

A catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction. Catalysts speed up reactions without being used up themselves.

Within living organisms, metabolic reactions are controlled by special catalysts called enzymes. Without enzymes, these reactions would take place very slowly or not at all - far too slowly to sustain life.

What are Enzymes? ⚡

Enzymes are proteins that are involved in all metabolic reactions, where they function as biological catalysts. They are called "biological" catalysts because they are made in living cells and maintain reaction speeds at a rate that can sustain life.

🔑 Key Point: Without enzymes, it would take around 2-3 weeks to digest one meal. With enzymes, digestion takes approximately 4 hours.

Why are Enzymes Important?

Enzymes are necessary to all living organisms because they maintain the reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life. Without enzymes:

  • Metabolic reactions would be too slow to support life processes
  • Digestion would take weeks instead of hours
  • Energy production would be insufficient
  • Growth and repair would be impossible

Examples of Enzyme Action

In the Digestive System:

  • Amylase catalyses the breakdown of starch to maltose
  • Protease catalyses the breakdown of proteins to amino acids
  • Maltase catalyses the breakdown of maltose to glucose
  • Sucrase breaks down sucrose
  • Lipases break down lipids (fats and oils) into fatty acids and glycerol

Breaking Down Harmful Substances:

Catalase catalyses the breakdown of hydrogen peroxide (a dangerous substance produced in cells) to harmless water and oxygen:

hydrogen peroxide→catalasewater+oxygen\text{hydrogen peroxide} \xrightarrow{\text{catalase}} \text{water} + \text{oxygen}

In Seed Germination:

When a seed soaks up water, amylase becomes active and breaks down stored starch into soluble maltose, which is then transported to the embryo for energy and growth.

Naming Enzymes 📝

Enzymes are named according to the reaction they catalyse, and their names often end in -ase:

Enzyme GroupSubstrateFunction
CarbohydrasesCarbohydratesBreak down carbohydrates
LipasesLipids (fats and oils)Break down lipids
ProteasesProteinsBreak down proteins
AmylaseStarchBreaks down starch to maltose
MaltaseMaltoseBreaks down maltose to glucose
SucraseSucroseBreaks down sucrose

The substance that an enzyme acts upon is called its substrate.

Sign in to view full notes