Enzymes

What are enzymes?

Chemically, enzymes are proteins.

They act as catalysts in chemical reactions.

The substances on which enzymes act are known as substrates.

Enzymes convert them into different molecules.

They catalyze chemical reactions by reducing their activation energy, thus increasing the rate of reaction.

Notes:

For a reaction to take place, these reactive sites have to be bought together.

This is where enzymes step in.

Because of its shape an enzyme has an area called the active site which can bring the reactive areas of two substrate molecules together.

The reactive site is a small area where it can react with other chemicals.

An enzyme-substrate complex is formed and the two chemicals react, joining together.

Lock and Key Model:

Induced Fit

In this model, when the substrate binds to the enzyme it may induce a change in the shape of the enzyme.

Once the product is released, the enzyme returns to its original shape.

Activation Energy Barrier:

A certain amount of energy is needed to get the reaction going.

Activation energy may also be defined as the minimum energy required to start a chemical reaction.

In the lab you can use heat to provide the energy, but a body uses enzymes, which lower the activation energy barrier.

Activation Energy Graph:

Denaturation of Enzymes:

Freezing does not affect enzyme activity whereas heating denatures the enzyme.

Denaturing enzymes can be either permanent or reversible.

Reversible denaturation occurs if you add a chemical such as urea. It will temporarily change the enzymes shape.

Irreversible denaturing takes place with heat. It breaks the covalent bonds in the protein.

Activity:

Summarise the notes on ‘Enzymes and the factors that affect them’ on page 96-97 of Patterns of Life.

Enzyme Action: (pg 89 L.S.)

Aim: To investigate the effect of temperature on enzyme action.

Notes: Hydrogen peroxide is a poisonous substance produced during cell respiration. Fortunately cells contain an enzyme peroxidase that very rapidly breaks down hydrogen peroxide into water and oxygen.

2H2O2 2H2O + O2

Method: Drop a little ground up raw liver into a test tube containing

5% hydrogen peroxide.

Use a glowing splint to test an gas given off. (Oxygen will cause a glowing splint to flare up.)

Repeat the activity with a piece of frozen and cooked liver.