# Explain how the structure of lactose and the enzyme lactase relate to the specificity of enzyme–substrate interactions in carbohydrate digestion.

> IB DP Biology Higher Level (2023 syllabus) — B1.1 Carbohydrates and lipids · Explain · 4 marks

> Lactose is a disaccharide found in mammalian milk. Individuals who do not produce sufficient lactase experience digestive discomfort after consuming dairy products.

## Mark scheme (4 marks)

1. Lactose is a disaccharide formed by a glycosidic bond between glucose and galactose.
2. The active site of lactase has a specific three-dimensional shape complementary to the structure of lactose.
3. Only lactose can form an enzyme–substrate complex with lactase, so other disaccharides (e.g. sucrose or maltose) are not hydrolysed by lactase.
4. Lactase catalyses hydrolysis of the glycosidic bond in lactose, releasing glucose and galactose for absorption; without sufficient lactase the disaccharide accumulates and causes osmotic/fermentation-related symptoms.

## Key terms

- [specificity](https://www.gradenine.co.uk/glossary/specificity)

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-lactose-b89c1793) · Published by Druglandscape Ltd.