Observing the Rate of Reaction of the enzyme Catalase upon changing Concentrations

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Valentina Zunarelli

IB Biology Practicals

Observing the Rate of Reaction of the enzyme Catalase upon changing Concentrations

Aim

To identify at which concentrations of salt solution (0%, 0.5%, 1%, 1.5%) the enzyme catalase (liver) works best and breaks down the most hydrogen peroxide.

Introduction

Enzymes are proteins that act as catalysts. They are made in cells. A catalyst is something that speeds up a reaction, but does not get used up in the reaction. One can usually be used many times. The majority of the reactions that occur in living organisms are enzyme-controlled. Without them, the rate of the reactions would be so slow as to cause serious, if not fatal, damage. Without enzymes toxins would soon build up and the supply of respiratory substrate would decrease. Enzymes, being proteins, have a specific shape. They are therefore specific in the reactions that they catalyse – one enzyme will react with molecules of one substrate. The site of the reaction occurs in an area on the surface of the protein called the active site. Since the active site for all molecules of one enzyme will be made up of the same arrangement of amino acids, it has a highly specific shape. Generally, there is only one active site on each enzyme molecule and only one type of substrate molecule will fit into it. This specificity leads to the lock and key hypothesis. However, it has been discovered that competitors for an active site (similar in shape to the substrate) could fit even though they are larger than the substrate. This means that the substrate and active site are a little flexible.

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Catalase is an enzyme found in food such as potato 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.

When there is an excess of enzyme molecules, an increase in the substrate concentration (salt solution), produces a corresponding increase in the rate of reaction. If there are ...

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