Enzymes (REVISION)

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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.


The substrate of an enzyme are the reactants that are activated by the enzyme.


An additional non-protein molecule that is needed by some enzymes to help the reaction.

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Tightly bound cofactors are called prosthetic groups.

Cofactors that are bound and released easily are called coenzymes.

Many vitamins are coenzymes.


Inhibitors are chemicals that reduce the rate of enzymic reactions. The are usually specific and they work at low concentrations.

They block the enzyme but they do not usually destroy it.

Many drugs and poisons are inhibitors of enzymes in the nervous system


Substrate concentration

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 ...

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