An Investigation into the Effect of Temperature on an Enzyme Catalysed Reaction.

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Rebecca Worley                                                                                        Biology

An Investigation into the Effect of Temperature on an Enzyme Catalysed Reaction.

The aim of our investigation is to show how various temperatures affects the rate at which oxygen and water are produced in the catalysed reaction of Hydrogen Peroxide.

The catalyst we are going to use is found naturally occurring in potato.

Background Information:

Enzymes can be divided into two main groups, intracellular and extracellular. Intracellular are found inside the cell, from where the control metabolism. These cells will also produce the extracellular cells, but these achieve their affect outside the cell. These include digestive enzymes that break down food in the gut.

An enzyme is named by adding the suffix – ASE to the substrate, which it acts upon. Hydrolase’s catalyse the hydrolysis of a substrate by the addition of a water molecule. Oxoreductases are involved with redox reactions. Transferases transfer a group of atoms from one molecule to another, and so on.

Enzymes are complex globular proteins, folded up into a precise 3d shape. They are made from a long polypeptide chain, which in a globular protein is wound and folded into a precise spherical shape. Hydrogen, ionic, disulphide bonds as well as hydrophobic interactions all hold the chain in its three dimensional shape.

The precise shape of the active site, the place at which the substrate is to bind, is so because the enzyme is specific to one substrate, hence the need for specificality. Thus meaning that the active site of an enzyme has a distinct chemical configuration to which only one substrate has the correct and complementary chemical configuration. This is known as the ‘ lock and key’ hypothesis.

An enzyme works by combining with the substrate molecule to form an enzyme – substrate complex. With their various bonds held into relation with each other, the substrate molecule then reacts to form the enzyme – product complex. This then splits into the enzyme and product(s). The enzyme remains unchanged by the reaction and is free to be used elsewhere.

Enzyme +                    Enzyme –                         Enzyme -                            Enzyme +

Substrate                Substrate complex              Product Complex                    Product

Catalase:

Catalase behaves as a catalyst for the conversion of hydrogen peroxide into water and oxygen.  Catalase is an example of a particularly efficient enzyme. Catalase has one of the highest turnover numbers for all known enzymes (40,000,000 molecules/second)2.  This high rate shows an importance for the enzymes capability for detoxifying hydrogen peroxide and preventing the formation of carbon dioxide bubbles in the blood

Catalase is composed of four subunits. Each subunit contains a heme group. This heme group is responsible for carrying out catalase's activity. Catalase functions to break down hydrogen peroxide (H2O2) into water and oxygen:

2H2O2                 2H2O + O2

This reaction is performed by oxidation, the loss of electrons, and reduction, which is the gain of electrons. Each of the sub-units in Catalase uses the energy from electrons to decompose the Hydrogen Peroxide.

Catalase functions by the oxidation of Iron within its heme group. This happens by removing an electron from 2 molecules of hydrogen peroxide (H2O2) to form 2 water molecules (H2O) and 1 oxygen molecule (O2)

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In Catalase, heme functions as a prosthetic group. A prosthetic group is a tightly bound, specific non-polypeptide unit required for the biological function of some proteins.

There are factors, which will control/affect the rate at which an enzyme-controlled experiment will take place. These include:

The Enzyme/Substrate concentration:

Providing conditions such as pH and temperature are at the normal for that specific enzyme, and there is an excess amount of substrate, then the arte of reaction will be directly proportional to the enzyme concentration. Increasing the amount of enzyme will increase the rate of reaction. If the amount of ...

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