Up Learn – A Level Biology (AQA) – Enzymes

Role and Structure of Enzymes

A reaction is catalysed by an enzyme when the substrate binds to it, forming an ‘enzyme-substrate complex’.
The induced fit model is one model for how an enzyme substrate complex lowers a reaction’s activation energy

More videos on Enzymes:

Factors Affecting Enzyme Controlled Reactions – Part 1

Role and Structure of Enzymes

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Up Learn – A Level Biology (AQA)


Here’s a reminder of the key points you need to know about the role and structure of enzymes.

All reactions require a minimum amount of energy to proceed, called activation energy. 

Enzymes are catalysts.

They lower the activation energy of a reaction without undergoing a permanent change themselves, which increases the rate of reaction.

Enzymes can catalyse a range of intracellular and extracellular reactions.

A reaction is catalysed when the substrate binds to a complementary active site on an enzyme

The shape of an enzyme’s active site is determined by the enzyme’s tertiary structure.

The induced fit model proposes that the enzyme’s active site and substrate initially aren’t completely complementary. 

When the substrate starts to bind, the active site changes shape to become complementary.

This puts stress on the substrate’s bonds, making them easier to break, and therefore lowers the reaction’s activation energy.