Investigation in to factors affecting the rate of an enzyme catalysed reaction.

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In the human body virtually every metabolic reaction that takes place is catalysed by an enzyme. Enzymes are globular proteins and their molecules are coiled with a precise three-dimensional shape. There are many different groups of enzymes each with their own jobs. An enzyme works by breaking down a substrate into its separate parts. Each group of enzymes works on breaking down different groups of substrates in different parts of the body.

Each enzyme and substrate when joined, act like a lock and key mechanism, the enzymes ‘unlock’ the substrate and out come the products. In order for this to work enzymes have a special site, which the substrate is attracted to. This is the enzymes active site, which is usually a cleft or depression to which the substrate can bind. Enzymes are designed so the substrate can fit perfectly into the active site, and to hold the substrate in place with temporary bonds that form between the substrate and some of the R groups of the enzymes amino acids.                

            There are many factors that affect the rate of enzyme reaction, for example, temperature, enzyme concentration, substrate concentration, pH and inhibitors. Enzymes are suited to the conditions in which they work in, for example protease pepsin; enzymes that work in the stomach are adapted to working in an area with a high pH. The same goes for temperature. Enzymes in the body have an optimum temperature of about 37°C, if they go too far above this temperature or too far below then the enzyme molecule begins to lose its shape and activity and becomes denatured. At low temperatures the reaction takes place only very slowly because the molecules are moving relatively slowly. Substrate molecules will not often collide with the active site and so the binding of the enzyme and substrate rarely happens. If the temperature is then increased collisions happen more frequently, so the substrate molecules enter the active site more often. Also when they do collide they have more energy making the binds easier to be broken. Until a certain point the more you increase the temperature the faster the reaction. Once this point has been reached the bonds holding the enzyme molecule in its shape begin to break, causing it to denature.

            A very similar thing happens with pH, most enzymes work fastest at a pH of about seven, which is fairly neutral, where as protease pepsin have a different optimum pH as it works in the stomach which has an acidic pH. If the pH falls too far above or below the optimum then this also denatures the enzyme.

            Enzyme concentration is another factor affecting the reaction rate, as the more enzyme present the more active sites will be available for the substrate to slot into. As long as there is plenty of substrate available the initial rate of reaction increases linearly with enzyme concentration. The same process applies to substrate concentration, as long as there is enough enzyme available then the reaction will increase, but if there is a low amount of enzyme then the reaction will decrease.

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           In many reactions in our bodies a chemical called hydrogen peroxide is produced as a bi-product. It is a metabolic poison and if not broken down results in cells death.

H20 2    H2O +    O2

Substrate + Catalase (Enzyme)  H2O +   O2

The enzyme catalase can bind with hydrogen peroxide molecules, split them into water and oxygen and release these products at a rate of 107 molecules per second.

        Does temperature affect the ...

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