Enzymes — GCSE Biology Revision
Revise Enzymes for GCSE Biology. Step-by-step explanation, worked examples, common mistakes and exam-style practice aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP.
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Go to The Heart & Circulatory SystemWhat is Enzymes?
Enzymes are biological catalysts that speed up chemical reactions in living organisms without being used up. Each enzyme has a unique active site that is complementary to a specific substrate, a model known as the lock and key theory. Factors like temperature and pH can affect the rate of enzyme activity.
Board notes: A core topic for all major boards (AQA, Edexcel, OCR). Students must understand the lock and key model, specificity, and the effects of temperature and pH, often through practical investigations.
Step-by-step explanationWorked example
Amylase is an enzyme found in saliva that breaks down starch (the substrate) into maltose (the product). If you hold a piece of bread in your mouth, it will start to taste sweet as the amylase gets to work. The active site of amylase is specifically shaped to fit the starch molecule.
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Common mistakes
- 1Thinking that enzymes are 'killed' by high temperatures. The correct term is denatured. High temperatures change the shape of the active site, so the substrate can no longer fit, and the enzyme becomes non-functional.
- 2Confusing the substrate with the product. The substrate is the molecule that the enzyme acts upon, and the product is what it is converted into.
- 3Believing that any enzyme can act on any substrate. Enzymes are highly specific; for example, lipase only breaks down lipids, and protease only breaks down proteins.
Enzymes exam questions
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Step-by-step method
Step-by-step explanation
4 steps · Worked method for Enzymes
Core concept
Enzymes are biological catalysts that speed up chemical reactions in living organisms without being used up. Each enzyme has a unique active site that is complementary to a specific substrate, a model…
Frequently asked questions
What is the lock and key model of enzyme action?
The lock and key model describes how an enzyme's active site (the lock) has a specific shape that only allows a particular substrate (the key) to bind to it. This explains enzyme specificity.
How does pH affect enzyme activity?
Every enzyme has an optimal pH at which it works best. If the pH is too high or too low, it can interfere with the bonds that maintain the enzyme's shape, causing it to denature and lose its activity.