AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Enzymes catalyse specific reactions in living organisms due to the shape of…
Full specification wording
The human digestive system: Enzymes catalyse specific reactions in living organisms due to the shape of their active site.
Enzymes are proteins that act as biological catalysts.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 5 of 25
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Enzymes are proteins that act as biological catalysts. Each enzyme has an active site, a region with a shape complementary to one particular substrate. Because shapes are specific, only that substrate binds, forming an enzyme–substrate complex. The enzyme lowers the activation energy needed for the reaction, so the reaction happens faster at body temperature. After the reaction, products are released and the enzyme is unchanged, ready to catalyse further reactions. This specificity explains why amylase acts on starch, protease acts on proteins and lipase acts on lipids. The lock-and-key idea helps describe how shape determines which reaction is catalysed, and it links directly to denaturation when shape is altered.
What earns the marks
- Enzymes are proteins that act as biological catalysts in living organisms.
- The active site has a shape complementary to a specific substrate.
- Substrate binds to the active site to form an enzyme–substrate complex.
- The enzyme lowers activation energy, increasing the rate of the specific reaction.
- Enzymes are specific because only substrates with a complementary shape can bind.
- Products are released and the enzyme is unchanged, so it can be reused.
- Named examples include amylase acting on starch, protease on proteins and lipase on lipids.
Common mistakes and how to put them right
Saying enzymes are used up in the reaction.
Put it right: Enzymes are catalysts and remain unchanged.
Stating that any substrate can bind to any enzyme.
Put it right: The active site is complementary to one specific substrate.
Confusing the active site with the whole enzyme.
Put it right: The active site is the specific region where the substrate binds.
Exam tips
- Use the terms 'complementary shape' and 'enzyme–substrate complex' to show precise understanding.
- Link each named enzyme to its substrate and product, for example amylase breaks starch into simpler sugars.
- Explain specificity by referring to shape, not by saying enzymes 'know' their substrate.
Try the lesson
The start of the The human digestive system: Enzymes catalyse specific reactions in living organisms due to the shape of their active site. lesson, made from checked teaching notes for this specification point.
Have a go first
Why is the shape of an enzyme's active site important for its function?
Listen
Enzymes are proteins that act as biological catalysts. Each enzyme has an active site, a region with a shape complementary to one particular substrate. Because shapes are specific, only that substrate binds, forming an enzyme–substrate complex. The enzyme lowers the activation energy needed for the reaction, so the reaction happens faster at body temperature. After the reaction, products are released and the enzyme is unchanged, ready to catalyse further reactions. This specificity explains why amylase acts on starch, protease acts on proteins and lipase acts on lipids. The lock-and-key idea helps describe how shape determines which reaction is catalysed, and it links directly to denaturation when shape is altered. A strong answer earns marks for these points. Enzymes are proteins that act as biological catalysts in living organisms. The active site has a shape complementary to a specific substrate. Substrate binds to the active site to form an enzyme–substrate complex. The enzyme lowers activation energy, increasing the rate of the specific reaction. A common slip: Saying enzymes are used up in the reaction. Instead, enzymes are catalysts and remain unchanged. Exam tip: Use the terms 'complementary shape' and 'enzyme–substrate complex' to show precise understanding.
Key words
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Biological catalysts
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Active site and substrate binding
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Enzyme specificity
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Digestive enzymes and their substrates
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See every definition
- Biological catalysts
- Proteins that act as biological catalysts in living organisms, lowering the activation energy needed for a reaction so it happens faster at body temperature.
- Active site and substrate binding
- The active site is a region with a shape complementary to one particular substrate, and only that substrate binds to form an enzyme–substrate complex.
- Enzyme specificity
- Only substrates with a complementary shape can bind, which explains why each enzyme catalyses a specific reaction.
- Digestive enzymes and their substrates
- Amylase acts on starch, protease acts on proteins and lipase acts on lipids.
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