Investigation: Enzyme Activity

Aim:

To investigate how the concentration of hydrogen peroxide effects the rate of reaction of an enzyme (catalase)

Variables:

These factors could effect the rate of reaction on an enzyme:

pH
Concentration
Temperature
Surface Area

pH - Enzymes function at different pH values. In neutral conditions the amount of oxygen gas given of in an enzyme-catalysed reaction will increase.

An enzyme is affected by how much acid or alkali is present. Many enzymes work best in neutral conditions but some prefer acids and some prefer alkalis.

This graph shows that the enzyme activity reacts best at pH7 (neutral)

Concentration - In concentrated solution there are more collisions between each particle, so the reaction occurs more quickly.

This graph shows that increasing the concentration increases the enzyme activity.

Temperature - Reactions go faster as temperature rises. The rate of reaction also increases as the temperature rises, but with enzyme-catalysed reactions the reaction rate starts to decrease when the temperature is above 40 C. This is because enzymes are proteins and their structures start to damage above 40 C.

This graph shows that the enzyme activity reacts best at 40°C as the enzyme starts to denature above 40°C

Surface Area - Reactions can react faster when solids are cut into smaller pieces. This is because there is more surface area which is exposed.

The more surface area there is, the more collisions that take place between particles so the reaction rate is much quicker.

This graph shows that small pieces react better than bigger pieces.

Brief Outline

I will test the effects of changing the level of concentration. For this variable I will use three different concentrations of hydrogen peroxide with catalase (enzyme). I will change the concentration whilst keeping the time, concentration of catalase and the volume of hydrogen peroxide constant.

I will begin all my tests at a constant temperature (room temperature) and I will repeat each test three times so I can obtain an average result.

Background Knowledge:

Lock and Key Model

A catalyst is a substance which alters the rate of reaction without being used up. Enzymes are the catalysts in biological processes. They are large proteins that speed up chemical reactions. The enzyme forms the active site from small numbers of amino acids.

The active site is the location on the enzyme where the substrate collides and the reaction takes place. If the shape of and the substrate do not match exactly then they do not bind. This makes sure that the enzyme does not work with the wrong reaction.

Enzymes are not affected by the reaction, so when the products have been released, the enzyme is ready to bind with a new substrate.

In my experiment the substrate was the hydrogen peroxide, the enzyme that we used was hydrogen peroxide and the product that was formed was oxygen and water.

This can be explained by an equation:

Enzyme + Substrate ⇒ Product

In my experiment this is shown as:

Catalase + H202 ⇒ H202 + 02

This equation explains how the catalase in our experiment binded with the H202 to break it down and form oxygen.

Induced Fit Theory

The induced fit theory states that the binding of a substrate to an enzyme causes a change in the shape of the enzyme.

The enzyme and the substrate act on each other to affect the making of the active site to the usual complex between the enzyme and its substrate. As a result, this means the enzyme to catalyze a reaction has changed.

This shows that enzymes are specific for specific substrates.

I can tell that the catalase in my experiment is a suitable enzyme to break down the H202 as it will form oxygen as a product which is unharmful

Denaturing

Denaturing is the damage to the protein structure of an enzyme. Most enzymes react faster as the temperature increases. Enzymes also react at low temperatures, but when the temperature rises above 40 C their reaction rate start to decrease. This is because enzymes are proteins and their structures get damaged when the temperature rises above 40 C.

When the protein is denatured it becomes less effective as a catalyst and soon the enzyme reaction gets slower and then finally it stops.

This is why enzymes in washing powders which clean by breaking down grease and other stains, cannot be used with hot water above 40 C

Activation Energy

In order for a reaction too occur activation energy must be supplied.

The activation energy is the energy required to start a chemical reaction.

Some elements and compounds react together to bring themselves into contact. For others it is necessary to supply energy in order to start the reaction. This energy is the activation energy.

Enzymes such as catalyst work by lowering the activation energy.

The Kinetic Theory of Matter

Everything is made of moving particles. The main points of the kinetic theory are:

All matter is made up of small particles called molecules
The molecules are always vibrating
The higher the temperature, the faster the molecules are moving
As the temperatures rises the particles get hotter. They have more energy and move around faster.

Solid Liquid Gas

Solid - In a solid the particles are very close together and have very strong forces between them. Solid particles can only vibrate, this is why they cannot flow. Solids have a fixed shape and a fixed volume

Liquid - In a liquid the particles are a little further apart. The forces are not very strong. Liquids can flow and change shape but they always have a fixed volume.

Gas - In a gas the particles are further apart. There are no forces to hold all the particles together. Thy move about very quickly in the space they find. Gases can flow easily and change their shape and their volume depending on the container.

Collision Theory

The collision theory explains chemical reactions and the way in which the rate of reaction alters when the conditions alter.

For a reaction to occur the reactant particles must collide. Only a fraction of the total collisions cause a chemical change. These are called fruitful collisions. The fruitful collisions have ...