Enzymes

This lesson covers the structure and function of enzymes as required by the Edexcel GCSE Biology specification (1BI0), Topic 1: Key Concepts in Biology. You need to understand how enzymes work, the lock-and-key model, the concept of specificity, and what happens when enzymes are denatured.

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What Are Enzymes?

Enzymes are biological catalysts. A catalyst is a substance that speeds up a chemical reaction without being used up or permanently changed in the process. This means an enzyme can be used over and over again.

Enzymes are proteins — they are made of long chains of amino acids folded into a precise 3D shape. This shape is critical because it determines which substrate the enzyme can act on.

Key Points

• Enzymes speed up reactions that would otherwise occur too slowly to sustain life.
• They work inside cells (intracellular enzymes, e.g. catalase in cells, DNA polymerase) and outside cells (extracellular enzymes, e.g. digestive enzymes in the gut).
• Enzymes are not living — they are molecules. But they are produced by living cells.
• Enzymes are highly specific — each enzyme catalyses only one type of reaction.