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OCR GCSE Chemistry A · J248
OCR J248 · C5.2i Check the specification (PDF) (opens in a new tab)
Living cells carry out chemical reactions to release energy, build substances and remove harmful materials. Some of these reactions would happen too slowly to support life without a . A catalyst makes a reaction faster but is not used up, so it can act again.
An enzyme is a protein that acts as a catalyst in a biological system, such as a living cell. Enzymes are therefore biological catalysts: they do the same essential job as other catalysts, but in the reactions of living things. For example, enzymes speed up reactions involved in digestion and respiration. Enzymes in cells also help break down harmful hydrogen peroxide into water and oxygen.
The substances being changed are the reactants; the enzyme is not one of the reactants being used up. Like other catalysts, it provides a route with a lower activation energy, allowing the reaction to proceed faster. An enzyme's shape helps it act on particular substances, rather than speeding up every reaction in a cell.
Enzymes are biological catalysts: proteins that speed up reactions in living systems without being used up. They help essential reactions, including digestion and respiration, happen fast enough to support life. Like other catalysts, they lower activation energy.
If asked what an enzyme does, state that it speeds up a reaction in a biological system without being used up.
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Put your knowledge into practice — try past paper questions for Chemistry A