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Effect of temperature

An increase in temperature, increases the kinetic energy between molecules, therefore more successul collisions between the substrate and the active site.

Each enzyme has an optimum temperature. Once this temperature is reached the enzyme begins to denature. This means that the active site's 3D specific shape is lost and is no longer complememntary to the substrate.

The denaturation of an enzyme is permenant.

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Effect of PH

Each enzyme has an optimum PH, at which the enzyme works best, and is the most productive.

This is why PH buffers are used. To maintain the PH of a solution to help stop the enzyme denaturing if the PH changed.

A change in PH alters the charges on the amino acids, which make up the active site. Furthermore the active site is no longer complementary and so there is a loss of enzyme-substrate complex producton.

A change in PH may also break the bonds in the tertiary structure of the globular protein and so will change the shape of the enzyme. Once it's unique tertiary structure has been changed it can no longer fulfill it's functions.

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Effect of substrate concentration

As the concentration of the substrate increases so will the rate of reaction. This is becasue there will be an increase in collisions between the substrate and the enzyme.

However there comes a point wher all the active sites are filled with substrate and so no more substrate can fit into the active site as they are already pre-occupied.

The rate of reaction is now at it's maximum.

This means that the substrate concentration is a limiting factor.

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Competitive Inhibition

Competitive inhibition:

  • Substrate an inhibitor are a similar shape.
  • The inhibitor beats the substrate for a place in the active site.
  • The inhibitor binds with the active site.
  • The inhibitor is not permenantly bound to the active site so it leaves and another molecule can take it's place.
  • If there is an increase in the substrate concentration then there will be a reduction in the inhibition concentration.
  • The inhibitor does not change the active site.
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Non-competitive inhibition

Non-competitive inhibition:

  • The substrate and the inhibitor are not a similar shape.
  • The inhibitor binds to the enzyme and not the active site.
  • However when it binds to the enzyme it changes the 3D shape specificness of the active site and so the active site is no longer complementary to the substrate.
  • Therefore the substrate can no longer fit in the active site.
  • If there is an increase in the substrate, it will not affect the concentration of the inhibitor.
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Enzyme action

The substrate fits into the active site of the enzyme. This active site is complementary to the substrate as the active site is 3D shape specific. This catalyses the reaction as the product formed is the Enzyme-Substrate Complex.

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Enzyme- A protein or RNA that acts as a biological catalyst. It alters the speed of a biochemical reaction. An enzyme is also a Globular protein

Catalyst- Something that increases the rate of reaction without being used up.

Active site- A group of amino acids  that make up the region of an enzyme into which the substrate fits. It is shape specific.

Substrate- A substance which fits into the active site. A substance that undergoes a chemical reaction.

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Induced fit model

The shape of the active site is not completely complementary but change specific in the prescence of a specific substrate to become complementary. 

When a substrate molecule collides with an enzyme, if its composition is specifically correct, the shape of the enzyme's active site will change so that the substrate fits into it and an enzyme- substrate complex can form. The reaction is then catalysed and an enzyme-product complex forms.

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Lock and key Hypothesis

It states that the shape and charge of the active sites of enzymes are exactly complementary to the shape of the substrate.

When the substrate collides with the enzyme whose active site is complementary, the substrate will fit into the active site and an enzyme-substrate complex is formed.

The enzyme will catalyse the reaction and the product, together with the enzyme, will form an enzyme-product complex

According to this model, it is possible for an enzyme to catalyse a reversible reaction.

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