Investigating the break down of Hydrogen Peroxide using celery tissue to supply the enzyme - Catalase

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Biology Investigation 5/12/01                                                                                             Jessica Roach

Investigating the break down of Hydrogen Peroxide using celery tissue

to supply the enzyme – Catalase

PLAN:

Aim: To investigate the rate at which hydrogen peroxide is broken down by the enzyme catalase by measuring the volume of oxygen produced.

Variables: Catalase is an enzyme that breaks down hydrogen peroxide into water and oxygen. The factors that affect the activity of catalase are:

· Enzyme concentration  

· Substrate concentration

· Temperature

· pH

The variable chosen to investigate is the concentration of the substrate Hydrogen Peroxide. The other variables will have to remain the same to ensure that it is a fair test.

Scientific knowledge:

Enzymes

Enzymes are biological catalysts; they speed up the rate of a chemical reaction whilst remaining chemically unchanged themselves. Enzymes are among the most powerful catalysts, and play an essential role in living organisms, where they accelerate reactions that would otherwise require temperatures that would destroy most of the organic matter.

Enzymes are made of proteins, in their globular structure, one or more polypeptide chains twist and fold, bringing together a small number of amino acids to form the active site, or the location on the enzyme where the substrate binds and the reaction takes place. If the shapes do not match exactly, the enzyme and substrate will not react. This ensures that the enzyme does not participate in the wrong reaction. The enzyme itself is unaffected by the reaction. When the products have been released, the enzyme is ready to bind with a new substrate.

This diagram shows clearly how an enzyme reacts with a substrate. This type of reaction is called a lock and key reaction. In order for an enzyme to react with a substrate it has to collide with enough energy that the enzyme and substrate can react. There are many factors that affect the speed of the collision between the enzyme and substrate.

The higher the concentration of the substrate the greater the number of collisions, which take place with the enzymes. If there is a large number of substrates then there is a higher chance that they will collide with an enzyme and result in a successful reaction. With more successful reactions taking place, there will be a larger volume of product given off.

Collision theory

Collision theory is used to predict the rates of chemical reactions, particularly for gases. The collision theory is based on the assumption that for a reaction to occur it is necessary for the reacting atoms or molecules to come together or collide with one another. Not all collisions, however, bring about chemical change. A collision will be effective in producing chemical change only if the atoms or molecules brought together possess a certain minimum value of internal energy, equal to the activation energy of the reaction. Furthermore, the colliding atoms or molecules must be oriented in a manner favourable to the necessary rearrangement of enzymes and substrates. Therefore, according to the collision theory, the rate at which a chemical reaction proceeds is equal to the frequency of effective collisions.

What constitutes an effective collision?

In order for a molecular collision to be effective it must meet two conditions:

The collision must have enough impact energy to overcome the Activation Energy. The Activation energy is the minimum energy necessary for product to form. This impact energy must be sufficient so that bonds can be broken within the reactant molecules and new bonds formed to produce the products.

The molecules must have a proper positioning for effective collisions to occur.

In this investigation the enzyme catalase is being used to break down hydrogen peroxide. Catalase is an enzyme found in food such as potato, celery and liver. It is used for removing Hydrogen Peroxide from the cells. Catalase speeds up the decomposition of Hydrogen Peroxide into water and oxygen. It is able to speed up the decomposition of Hydrogen Peroxide because of the shape of the Hydrogen Peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is called an anabolic reaction.

Catalase is a very fast reacting enzyme, it is found in many living cells. In fact one molecule of it can deal with six million molecules of hydrogen peroxide in 1 minute. Hydrogen peroxide is toxic so needs to be changed into harmless substances. This information was found in textbooks and on Encarta where the functions and uses of enzymes, specifically catalase, were researched.

In my investigation I will study the effect of substrate concentration on the rate of catalase activity.

Formula:

Hydrogen Peroxide Water + Oxygen

         H2O2 (aq)   H2O (l)   +  O2 (g)

To test how much the rate of the products will increase as the substrate concentration increases the experiment will need to be carried out a number of times using different concentrations and recording the volume of gas given off at each of the different concentrations. Also it is possible to tell whether the correct gas is given off, because it is known that if a glowing splint is put into a test tube containing oxygen the splint will relight showing oxygen is present.

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Variables affecting the rate of enzyme reaction

        PH level is a factor because enzymes will only function well at an optimum pH value; this is normally 7 because enzymes are proteins which are damaged by very acidic or very alkaline conditions. If the pH level changes then the enzymes become denatured and do not function properly.

        Temperature is a variable in the experiment because of the nature of enzymes. Enzymes all work best at an optimum temperature, which is usually body temperature at 37C. If the temperature that the enzyme has to work at gets too high, normally 40C it ...

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