The effect of a competitive inhibitor on the rate of reaction.

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The effect of an competitive inhibitor on the rate of reaction

Nature of the problem

There have been many problems with pollution, which have affected agriculture. An example of this is pollution from coal mines in area such as Sheffield. Ions such as copper, leak from the mines into the soil in nearby fields. These fields are used to grow crops on. When leaching of metal ions occur from coalmines it can affect crops growing in near by fields. The ions get into the soil and affect the growth of the crop by acting as inhibitors and not allowing enzyme substrate complexes to form; an example of this is what will be investigated in the investigation – copper II sulphate ions leach from the coalmines and get into the soil affecting the rate at which the catalase in celery is broken down.                      

In the case of catalase the active site is the haem group. Competitive inhibition occurs because the inhibitor has a similar shape to the substrate, and due to the ‘lock and key’ theory can bind to the active site. Copper sulphate is a competitive inhibitor of catalase.

   Enzymes are proteins which are responsible for catalysing almost every metabolic reaction which can occur in living organisms. Most enzymes catalyse only one type of reaction, so each living organism requires thousands of different enzymes. These biological catalysts are important because they speed up the rate of the reaction they catalyze that would otherwise be too slow to support life.

Catalase is an enzyme that is located in a cell organelle called the peroxisome. It is present in the cells of plants, animals and aerobic (oxygen requiring) bacteria Peroxisomes in animal cells are involved in the oxidation of fatty acids, and the synthesis of cholesterol and bile acids. Hydrogen peroxide is a by-product of fatty acid oxidation. White blood cells produce hydrogen peroxide to kill bacteria. In both cases catalase prevents the hydrogen peroxide from harming the cell itself. Peroxisomes in plant cells are involved in photorespiration (the use of oxygen and production of carbon dioxide) and symbiotic nitrogen fixation (the breaking apart of the nitrogen molecule N2 to reactive nitrogen atoms). Hydrogen peroxide is produced as an intermediate during these chemical processes and must be removed to prevent damage to cellular machinery. Aerobic (oxygen requiring) bacteria produce hydrogen peroxide as a by-product of metabolism.

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A catalase molecule is a  tetramer of four polypeptide chains, with each chain comprising of over 500 amino acids. There are  four porphyrin- haem groups in the tetramer that are very much like the familiar haemoglobins, cytochromes, chlorophylls and nitrogen-fixing enzymes in legumes. The haem group is responsible for catalase’s enzyme activity. Catalase has one of the highest turnover rates for all enzymes: one molecule of catalase can convert 6 million molecules of hydrogen peroxide, a powerful and potentially harmful oxidising agent, to water and oxygen each minute;

2H2O2                          ...

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