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Investigation of how PH affects the action of the enzyme catalase.

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Introduction

Investigation of how PH affects the action of the enzyme catalase Aim: The aim of this investigation is to discover the affects of PH on the enzyme catalase. Hypothesis: The enzyme calatase has an optimum PH at which it will catalyse a reaction. A PH above or below the optimum level will result in the enzyme not working at it's potential, causing it to decrease the reaction rate, or denature. The optimum PH at which the enzyme catalase will function correctly is around seven (neutral). The hypothesis explained What are enzymes? Enzymes are globular proteins that control reactions in living cells. They are biochemical catalysts, speeding up reactions that would otherwise happen too slowly to be of any use to the organism. An active enzyme may speed up a particular reaction, but living things do not need reactions to be carried out at a constant speed all the time. Enzymes interact with simpler molecules to produce an ordered, stable reaction system in which the products of any reaction are made when they are needed, and the amount needed. The specific shape of enzymes An enzyme has a specific three-dimensional shape and an active site, onto which the substrate joins during a reaction. If the enzyme and substrate are able to fit together, they are said to have complementary shapes. Each enzyme's active site has it's own three-dimensional shape, therefore, only a substrate with that particular complementary shape will fit. A short-term bond, known as a binding is created between the substrate and active site, which causes the substrate to react more rapidly. Enzymes are described as specific as they will only catalyse certain reactions. Enzymes are proteins, and the three-dimensional structure determines the function of the enzyme. The enzyme is made specific by the active site. The diagram shows a simplified active site, which is held together by different bonds, such as hydrogen bonds, and ionic bonds. ...read more.

Middle

These reduce the activation energy by joining to the enzyme or substrate, and are known as activators, which are believed to create the enzyme-substrate complex more easily. An example is the action of amylase on starch, which occurs more quickly in the presence of chloride ions. * A coenzyme is also a co-factor, which will momentarily join to the active site of the enzyme and take part in the reaction. A link between two different reactions can be made with a coenzyme. * A coenzyme that is permanently joined to the enzyme by a covalent bond is called a prosthetic group. This assists the enzyme to act as a catalyst. Enzyme Cofactor Substrate (c)James K. Hardy and the University of Akron. The effect of temperature on the rate of reaction The graph indicates the effect that temperature has on reaction rate. Due to the low temperature, and therefore kinetic energy, then enzyme and substrate at A travel slowly. This results in a slow rate of reaction as there are very few successful collisions between the molecules. An increase in temperature will provide the enzyme and substrate molecules with more kinetic energy, which will result in an increased number of successful collisions between the molecules. The number of enzyme-substrate complexes will also increase with the reaction rate. It is these factors that will determine the rate of reaction. For these reasons, the rate of reaction will increase with the temperature, as shown by the graph. The substrate and enzyme molecules will have a large amount of kinetic energy at a high temperature. Molecules vibrate as a result of kinetic energy. Therefore, an increase in temperature will cause the molecules to vibrate more. The shape of the enzyme will change if the hydrogen bonds are broken, i.e. the enzyme will denature. This will happen if the molecules have a large amount vibrational energy. By observing the graph, denaturing of the enzyme is taking place between points B and C. ...read more.

Conclusion

Each of the subunits in catalase uses the energy from electrons to decompose (breakdown) hydrogen peroxide. Catalase is found in all animal organs, particularly in the liver. The enzyme is also found in plant tissues and in nearly all aerobic microorganisms. A large number of catalase enzymes have been found in bacteria. An example of the biological use of this enzyme occurs in the bombardier beetle. The beetle uses a peroxidase to synthesize a quinone which causes a stinging sensation when sprayed on its victim. The beetle delivers this noxious liquid using the very exothermic catalase reaction to generate steam as the propellant. Heme's Structure 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. Heme consists of a protoporphyrin ring and a central iron (Fe) atom. A protoporphyrin ring is made up of four pyrrole rings linked by methene bridges. Four methyl, two vinyl, and two propionate side chains are attached. The iron can either be in the ferrous (Fe++) or the ferric (Fe+++) oxidation state. Catalase functions by the oxidation of Iron within its heme group, as shown below. Catalase functions by removing an electron from two molecules of hydrogen peroxide (H2O2) to form two water molecules (H2O) and one oxygen molecule (O2). Colour code Oxygen | Carbon | Nitrogen | Hydrogen | Iron (c)Brannon Carter and Robin L. Carter Examples of processes that produce H2O2 Peroxisomes partially oxidise fatty acids producing H2O2 as a by-product. This peroxisomal oxidation shortens the fatty acids to length C8 or longer and facilitates an energy efficient deprivation in the mitochondrion. The peroxisomal oxidation is slightly less efficient at ATP production than mitochondrial oxidation. However, it does not waste much of the available energy. Some of the "missing energy" is stored away in the oxidative power of H2O2 which is used in the peroxidative reaction. Both of these reactions are catalysed by catalase. The hydrogen peroxide disproportionation and the peroxidative reaction consume H2O2. Catalase activity in the cell is therefore an important process. Daniel O'Farrell 12F1 ...read more.

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