Show that the copper found in copper copper(II)sulphate is indeed a non-competitive inhibitor of the enzyme called catalase which is mainly found in the liver.

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Introduction

 

Catalase is an enzyme that consists of a protein complex with haematin groups and catalyses the decomposition of hydrogen peroxide into water and oxygen, this equation shows this.

2H O                        2H O  +  O

Free radicals are produced in most cells of the body as a byproduct of metabolism, although some cell types manufacture larger quantities for specific purposes. The most important free radicals found in aerobic cells, such as those in humans, are oxygen, superoxide, hydroxyl radical, hydrogen peroxide, and the transition metals.

When free radicals form within cells they can oxidise biomolecules (molecules used inside cells, especially lipids) and thus cause cell death and injury. However, the human body has developed various mechanisms in order to protect itself from the damaging effects of free radicals. One of these mechanisms are enzymes, such as catalase which decompose peroxides and transition metals in the liver.

A simple definition of an enzyme would be that they are protein molecules that act as biological catalysts.  Enzyme molecules are globular proteins.  The shape of an enzyme molecule is a precise 3-dimensional shape, with hydrophilic R groups on the outside of the molecule ensuring that they are soluble.  The properties that are possessed in the structure of the enzyme molecule are shared with all other globular proteins.  Enzymes are specialized molecules, the special feature being an active site.  The active site of an enzyme is a region to which another molecule or molecule can bind to as stated in Biology 1 (Page 42).  The active site is often perfectly shaped so that the substrate can fit.  

Each type of enzyme will usually bind with one type of substrate molecule.  The reason this happens is that each type of enzyme has a different shape that is only specific to one type of substrate molecule.  This concept is shown in diagram 1 below.

Diagram 1

As you can see enzyme A and substrate A fit perfectly as the active site and the substrate are the same shape.  Diagram 1 also shows that substrate B and Enzyme A do not fit together properly as the active site on Enzyme A is not the same shape as the substrate B molecule.  From this we can determine that enzyme A is specific for only substrate A and not substrate B.

The function of an enzyme is to lower the activation energy so that the reaction could take place at a lower temperature, but that is not always the case.  Nearly all enzymes are specific to one type of substrate molecule, but there are other molecules that are very similar to the enzymes substrate and can bind to the enzyme rather than the substrate.  Theses molecules are referred to as inhibitors for the simple reason that they inhibit the enzymes functions.

Heavy metals tend to be non-competitive inhibitor, which means that they inhibit the action of the enzyme-controlled reactions by attaching themselves to the enzyme molecule outside of the active site, thereby preventing the enzyme carrying out its normal catalytic function.  In this case, the extent of the inhibition depends entirely on the concentration of the inhibitor and cannot be varied by changing the amount of substrate present.  

Aim

The aim of this experiment is to be able to show that the copper found in copper copper(II)sulphate is indeed a non-competitive inhibitor of the enzyme called catalase which is mainly found in the liver.

Prediction

I predict that as the concentration of copper(II)sulphate increases, inhibition on the enzymes will be greater, thus the slower the rate of the enzyme-controlled reaction. I think that at the end of the experiment the rate of reaction would generally be reduced by up to 50% if the concentration is reduced by the same percentage.

Variables

Before the experiment can commence all the variables that could hold a bearing on the results must be discussed, and also to determine which variables would be kept constant during the experiment and which variable would be altered aster each test.

Temperature

The temperature affects the rate of reaction significantly.  The reason to this is that enzymes work at different rates depending on the temperature.  Enzymes work at the optimum rate at between 37°C to 40°C, any higher and the enzymes will denature and cease to work properly.  The reason the enzyme denatures is that at moderately high temperatures the hydrogen bonds that support the structure of the enzyme breaks down, therefore the enzyme would loose its 3-D structure and collapse.  If the temperature becomes too low the rate of reaction will slow down and not enough oxygen will be released.

Concentration of Substrate

The amount of substrate affects the rate of reaction.  The reason this happens is that if there is more substrate then there are enzymes then there will be less collisions between the substrate and the enzyme, then the rate of reaction will be at the optimum and over time it will eventually slow down and the reaction will stop.  If the amount of substrate is very small then there will be less substrate then enzymes there fore there will be a slower reaction, as most enzymes will be waiting to bind with a substrate molecule.

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Concentration of Enzymes

The amount of enzymes affects the rate of reaction.  The enzyme molecules bind with the substrate molecule to lower the activation energy of the substrate.  If there are more enzyme molecules present then substrate molecules there would be more collisions between the enzymes and the substrates.  Increased chances of there being a collision would increase the rate of reaction, when the number of enzyme molecules exceeds the number of substrate molecules then the rate of reaction will not increase further.

Concentration of Inhibitor

If the concentration of the inhibitor is high then a higher number ...

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