An Investigation into the Rate of Breakdown Of Hydrogen Peroxide By Potato Tissue

An Investigation into the Rate of Breakdown Of

Hydrogen Peroxide By Potato Tissue

Initial Observations: -

Hydrogen peroxide solution is toxic.
Hydrogen peroxide slowly beaks down to oxygen and water.
All living cells contain the enzyme catalase.
Catalase/living cells cause hydrogen peroxide to break down quickly.

Hypothesis: -

I predict that the greater the surface area the more oxygen will be produced in the first five minutes of collecting oxygen.

Each enzyme has an active site, which is an area of a particular shape into which only one type of molecule will fit. For this reason enzymes are specific to their substrate. The enzyme catalase splits hydrogen peroxide as follows: -

hydrogen peroxide oxygen + water

2H O O + 2H O

The above reaction will only occur when the hydrogen peroxide molecule collides with a catalase molecule. The more collisions there are, the larger the volume of oxygen produced.

If the temperature is increased there will be more successful collisions because the molecules have more energy so they move faster and collide more frequency. The collision will also have more energy so more catalase will be successful so therefore there will be more oxygen produced.

It is for this reason that temperature in my investigation must be controlled. If the temperature is not controlled then the oxygen being produced has not just been produced from the surface area but also from the temperature. If the temperature is changed as well as the surface area then the oxygen is being produced by two variables.

Enzymes

Enzymes are proteins. A protein is made up of a series of amino acids, which are unique to that protein. This is known as the proteins primary structure. If the enzyme is deformed in any way, then it will not be the right shape and will not function. Each enzyme has its own specific shape, with a gap at a different position. This gap is the Active Site and this is where the substrate binds with the enzyme.

Without an enzyme, molecules can still react by colliding with each other (see collision theory), but there is need for energy to be applied. For reactions to take place molecules or substrates have to collide with a large amount of energy to break and form bonds, which creates the products. This energy needed to make the substrate react to form the products is called the Activation energy.

Bonding for Reactions

For a reaction to take place a substrate molecule has to bond with an active site of an enzyme. Usually the substrate molecule is smaller than the enzyme’s active site. When the substrate bonds with the enzymes active site they slot into the active site like a key to the right lock. When they slot into the active site they are closer to the amino acids, which form the enzyme. The active site was first though of as a negative impression of the substrate. This idea was called “Lock and Key”.

The “Lock and Key” theory

This enzyme was pictured as a rigid structure, with an active site exclusive to the substrate. When substrate bonds with an enzyme, it changes the shape of the enzyme’s active site. The amino acids in the active site mould to the shape of the substrate, to allow the enzyme to perform its catalytic function. This method is called the induced fit because of the ability of the active site to mould to the shape of the substrate.

The Induced Fit theory.

Once the reaction has occurred then the substrate, which is not bonded to the active site any more, simply diffuses away and the active site returns to it’s original status and shape. Once it has returned to its original shape it is able to bond with another substrate.

Enzyme Reactions

The enzyme combines with the substrate, forming an enzyme-substrate compound. The ‘equation’ for the enzyme-substrate compound is:

Enzyme + substrate enzyme-substrate complex

E + S ES

When the enzyme-substrate compound breaks down to give the products, it releases the enzymes in an unchanged form:

Enzyme-substrate complex products + enzyme

ES P + E

This can be represented in diagrams.

Enzyme controlled reaction

Effect of Temperature on Enzymes

The graph (below) shows us how an enzyme reacts with different temperatures. The enzyme reaction is measured by how much substrate or the amount of product is made during a specific period of time.

At low temperatures, for example below 30°C when increasing the temperature more heat energy is produced. Increasing the temperature also increase the kinetic energy causing the enzyme and substrate molecules to move faster and to collide more frequently.

As the temperatures increase further the enzymes and substrates move even faster. But, because of the speed of the collisions some of the bonds of the enzyme break. As the bonds break the enzyme loses its shape and the active site is affected, causing the substrate to no longer fit into it. This is when the enzyme is denatured ...