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Factors affecting enzyme activity.

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Factors affecting Enzyme Activity Enzymes are biological catalysts. Enzymes have specifically shaped active sites. The shape of the active site is complementary to the shape of the substrate molecules involved in the reaction. This means that the substrate molecules which are usually much smaller than the enzyme molecule, can fit into the active site. This is described as the lock and key hypothesis. This is because the substrate key fits into the active site lock. The substrate is then held in one place so the reaction can go ahead. This allows the active site to fit more closely around the substrate, The substrate is held in place because of oppositely charged groups on the substrate and active site are located close to each other. This is known as an enzyme-substrate complex. Due to the change in shape of the enzyme, the substrate molecule is destabilised; this allows the reaction to go ahead with ease. ...read more.


Consequently the shape of the active site changes due to the change in the charges around the active site, when the pH is changed, this in turn changes the rate of the enzyme-controlled reaction. This occurs because more hydrogen ions are attracted towards the negatively charged groups in the active site. All enzymes have their own unique optimum pH, at which the rate of reaction is highest, which is generally pH7. At this optimum pH, an effective overall shape is given to the tertiary structure of the enzyme by the hydrogen ions. Therefore the active site is held in the best possible shape the substrate can complementarily fit into. When the pH is changed, or the concentration of the hydrogen ions is modified, the reaction rate decreases rapidly. This is because the shape of the enzyme molecule is altered which in turn changes the shape of the active site. ...read more.


The level of inhibition is dependent on the concentration of the inhibitor and substrate. The level of inhibition decreases when the amounts of substrate molecules are increased. This is because a substrate molecule is more likely to collide with an active site than an inhibitor molecule. There is no competition between non-competitive inhibitors and substrate molecules for a place within the active site. They attach on to the enzyme molecule in a location that is distant form the active site. This distorts the tertiary structure of the enzyme molecule which in turn changes the shape of the active site. Therefore the substrate can no longer fit into the active site, which prevents enzyme-substrate complexes from forming and the reaction rate s decreased. The level of inhibition is dependent on the amount of inhibitor molecules present. The enzyme controlled reaction will halt if there are enough inhibitor molecules to bind to all the enzyme molecules present. This type of inhibition is not affected by changing the substrate concentration. ...read more.

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