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Enzymes (REVISION)

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ENZYMES A protein with catalytic properties due to its power of specific activation. Chemical reactions Chemical reactions need an initial input of energy = THE ACTIVATION ENERGY During this part of the reaction the molecules are said to be in a transition state. One way to reach the transition state rapidly is to increase the temperature. But biological systems are very sensitive to temperature changes. Enzymes can increase the rate of reactions without increasing the temperature. They do this by lowering the activation energy. They create a new reaction pathway ?a short cut?. Enzyme controlled reactions proceed 108 to 1011 times faster than corresponding non-enzymic reactions. Substrate The substrate of an enzyme are the reactants that are activated by the enzyme. ...read more.


The effect of pH Extreme pH levels will produce denaturation. The structure of the enzyme is changed. The active site is distorted and the substrate molecules will no longer fit in it. At pH values slightly different from the enzyme?s optimum value, small changes in the charges of the enzyme and it?s substrate molecules will occur. This change in ionisation will affect the binding of the substrate with the active site. Note: The pH at which the enzyme molecule?s charges are equal is called it?s isoelectric point. This corresponds to its optimum pH. On an electrophoresis gel the enzyme would not move as it has no overall charge at this pH. The effect of temperature Q10 (the temperature coefficient) ...read more.


Reversible inhibitors: These can be washed out of the solution of enzyme by dialysis. There are two categories. Competitive: These compete with the substrate molecules for the active site. The inhibitors action is proportional to its concentration. Usually this type of inhibitor resembles the substrate?s structure closely If more substrate is added, the effect of the inhibitor is reduced. Non-competitive: These are not influenced by the concentration of the substrate. It inhibits by binding irreversibly to the enzyme but not at the active site Examples Cyanide combines with the Iron in the enzymes cytochrome oxidase. Heavy metals, Ag or Hg, combine with ?SH groups. These can be removed by using a chelating agent such as EDTA. Applications of inhibitors Negative feedback See end point or end product inhibition Poisons snake bite, plant alkaloids and nerve gases. Medicine antibiotics, sulphonamides, sedatives and stimulants ...read more.

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