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Enzyme-controlled reaction.

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I may be able to carry out an investigation into the rate at which substrate is converted into product during an enzyme-controlled reaction. In a specific enzyme controlled reaction, the substrate molecules combine with the active site of an enzyme, as in all hydrolysis reactions, water participates in the breakdown, with the release of 'products' which diffuse back into the environment around the active site. The process continues as long as there are substrate molecules to be converted, as the enzyme molecule is unchanged at the end of the reaction. The enzyme itself is found in the tissues of most living things and catalyses the breakdown of hydrogen peroxide into water oxygen. It is an easy reaction to follow as the oxygen that is released can be collected and measured. For example looking at the diagram below:- Enzyme concentration At low enzyme concentration there is great competition for the active sites and the rate of reaction is low. As the enzyme concentration increases, there are more active sites and the reaction can proceed at a faster rate. Eventually, increasing the enzyme concentration beyond a certain point has no effect because the substrate concentration becomes the limiting factor. ...read more.


The graph below illustrates the effects of substrate concentration on a 'reaction'. Temperature activity Enzymes work best at an optimum temperature. Below this, an increase in temperature provides more kinetic energy to the molecules involved. The numbers of collisions between enzyme and substrate will increase, so the rate will too. Above the optimum temperature, and the enzymes are denatured. Bonds holding the structure together will be broken and the active site loses its shape and will no longer work. Therefore at low temperatures, the reaction takes place only very slowly. This is because molecules are moving slowly. In order to have more impact in collisions with enzyme active site and the substrate, rising the temperature to a certain level is essential. Not only the amount of collisions increase, also they do so with more energy as this makes it easier for bonds to be broken so that reaction can occur. The optimum temperature for most human enzymes is around 40 C. A slight rise above this would begin to denature enzymes. This graph below is an example of a how temperature could affect the rate of a reaction. pH activity As with temperature, enzymes have an optimum pH. ...read more.


Non-competitive reversible inhibitors: these molecules are not necessarily anything like the substrate in shape. They bind with the enzyme, but not at the active site. This binding does change the shape of the enzyme though, so the reaction rate decreases. Irreversible inhibitors: These molecules bind permanently with the enzyme molecule and so effectively reduce the enzyme concentration, thus limiting the rate of reaction, for example, cyanide irreversibly inhibits the enzyme cytochrome oxidase found in the electron transport chain used in respiration. If this cannot be used, death will occur. However metabolic reaction must be finely controlled and balanced, so no single enzyme can be allowed to 'run wild', constantly churning out more and more product. One way of ensuring that this cannot happen is to use end product of a chain reactions as an enzyme inhibitor. For example:- As the enzyme converts substrate to product, it is slowed down because the end-product binds to another part of the enzyme and prevents more substrate binding. However, the end-product can lose its attachment to the enzyme and go on to be used elsewhere, allowing the enzyme reform into its active state. As product level falls, the enzyme is able to top them up again. This is end-product inhabitation and is an example of non-competitive reversible inhabitation. ...read more.

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