Enzyme action

First step of enzyme action

Substrate must collide with the active site of an enzyme in the correct orientation and with enough energy.

Second step of enzyme action

Substrate binds to active site to form an enzyme-substrate complex (ESC).

Third step of enzyme action

Substrates are converted into products.

Fourth step of enzyme action

Products are released so the active site is available to bind to another substrate.

What are the two models used to represent enzyme action

Lock an key model

Induced fit model

What is the difference between the lock and key model and the induced fit model

In the lock and key model, the shape of the active site never changes however in the induced fit model, the substrate binding to the active site causes its shape to change.

Which model is more widely accepted and why

The induced fit model is more widely accepted as it is supported by more recent evidence.

Activation energy

The amount of energy needed to get a reaction to start.

What do enzymes do to the activation energy

They lower it so less energy is required for the reaction to take place.

What is the effect of lowering the activation energy

There will be more frequent successful collisions between the substrate and enzyme active site and the rate of reaction will increase.

Why might R groups at the active site be oppositely charge to the substate

To assist binding.

Why does the active site change shape as the substrate binds

So that it is complementary in shape to the substrate in the ESC.

Why does the substrate change shape as it binds to the active site

Strains the bonds in the substrate so the break more easily.

Why does the enzyme stabilise the transition state

So the activation energy to form the transition state is lower.

Why do enzymes provide alternative reaction pathways

To provide an alternative transition state which has lower energy.