Enzymes … what do you know and will find out these next few

lessons

Lets find out millionaire styley remember the tips from “Mrs B

how to answer MCQ”

• Recap enzyme properties, activation energy and factors affecting enzymes

• Explain the induced fit theory• Examine the effect of substrate concentration

Quick Recap ...

• Enzymes made of proteins (affected by temp & pH)• Active site (AS) where it binds to one specific substrate

(affinity of one substrate)- denature alters AS• Enzymes are biological catalysts;

– Lower activation energy required for a reaction to proceed

(done by reactants forming unstable

transition state which will form products)

– Speeds up the rate of reaction of a reaction– Takes part in a reaction but remains unchanged at the end

of it

Old model of enzyme -

The old idea of enzymes working with their substrate like a “lock and key” is over-simplistic.

Better is the Induced fit model ....

.

.

• where the substrate molecule induces (a slight change in the shape of the active site to allow the substrate molecule to fit perfectly)

• The change in shape of the active site makes the reaction take place more easily.

• After the reaction is over, the product is released and the active site returns to its normal shape and the enzyme is free to attach to more substrate

Induced Fit Model

• Proposed by Daniel Koshland and is now widely seen as the preferred model

• However when he first proposed it some resistance difficult getting scientific journals to published his work

• Indirect support – such as certain chemicals, known not to bind to the active site, altered the binding and catalysis of the substrate (non-competitive inhibition)

• Eventually direct support such as visualising the active site by X-ray crystallography

Induced Fit Model

• It showed;

• The activity of enzymes depends on their flexible and dynamic shape. The affinity of substrate molecules for the active site of an enzyme and induced fit.

Hint - like hands into a small

rubber glove!

Draw these pictures / add labels and describe what is going on using these key words.....

• Active site• Orientation• Substrate

• Induced • Chemical bonds • Affinity

1. The active site determines the orientation of the reactants, allowing for them to held so a reaction can occur.

2. The chemical bonds weaken, which reduces the activation energy for the reactants to reach transition state.

3. Finally the products have a low affinity to the active site and are released.

4. Active site free for new substrates.

Orientation of reactants

What factors affect enzyme action?

What factors affect enzyme action?

• Suitable temperature• Appropriate pH• Correct substrate• Adequate supply of substrate• Presence of an inhibitor (more next time)

For example the direction in this metabolic pathway if substrate W becomes available enzyme 1 becomes active and converts to X and so one. A continued supply of W ensure the direction drive. Most metabolic reactions are reversible – depending on concentration as pathways are rarely isolated. So alternatively could go back to X if Y concentration high. Enzymes often act in groups; multi-enzyme complex like DNA/RNA polymerases.

LO3 – Enzyme activity .....

• Substrate concentration – hydrogen peroxide concentration

• Enzyme concentration – L-Dopa and banana (+colorimeter)

• Read what is expected of your plan/design/ execution of experiment and write up

Homework

• Complete your plan

• Next two lessons – carry out and write up your LO3