Enzymes and Biological Catalysts

This lesson covers the structure and function of enzymes as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand the lock and key model, the role of the active site, what denaturation means, and how enzymes function as biological catalysts with optimum conditions.

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What Are Enzymes?

Enzymes are biological catalysts — they speed up chemical reactions in living organisms without being used up in the process. Without enzymes, the chemical reactions in cells would occur too slowly to sustain life.

Key facts about enzymes:

• Enzymes are proteins — they are made of long chains of amino acids folded into a specific 3D shape.
• Each enzyme catalyses a specific reaction — this is because of the unique shape of the enzyme's active site.
• Enzymes are not changed or used up during the reaction, so they can be reused.
• Enzymes work inside cells (intracellular, e.g. respiration enzymes) and outside cells (extracellular, e.g. digestive enzymes).

Exam Tip: The key word is "specific". Each enzyme only works on one type of substrate. This specificity is determined by the shape of the active site.

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