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Year 12 Enzymes Project
Enzymes are organic catalysts. This means that they speed up the rate of a chemical
reaction without being used up themselves. They are very specific and only work with
certain substrates. A substrate the substance that the enzyme combines with. Each
enzyme is responsible for a single reaction within the cell.
1. Active site
For two molecules, or an enzyme and its substrate to react with each other they must
collide, firstly with sufficient force and also from the right direction or orientation.
The force needed to overcome the energy barrier and to allow a reaction to take place
is called the activation energy. An enzyme lowers the activation energy required. It
must also have the right orientation as enzymes have what is called an active site.
This is part of the molecule it is the right shape for a certain substrate and has the
functional groups needed to bind one of the reacting molecules, or substrate.
2. Lock and Key Hypothesis
The lock and key hypothesis is brought about because both the substrate and the
enzyme are very specific. Each enzyme targets a specific substrate which matches the
shape and size of the enzyme. Once the substrate and enzyme come together the new
compound is activated and formed. In this analogy, the enzyme is the lock and the
substrate the key.
Diagram 1 ­ Enzyme and Substrate
3. Induced fit Hypothesis

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The induced fit model is a modification of the lock and key model. The enzyme
molecule changes shape as the substrate molecules gets close. The change in shape is
'induced' by the approaching substrate molecule. This is because the molecules are
flexible because single covalent bonds are free to rotate. As the substrate molecule
enters the active site it changes shape, the active site then changes shape until the
substrate is completely bound.…read more

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However if the substrate concentration increases but the concentration of enzyme
molecules stays the same the rate of reaction will increase as substrate concentration
increases but only up until the point where all enzyme molecules are being used. This
is the point of saturation. The enzyme/substrate has to dissociate before the active
sites are free to accommodate more substrate.
3. pH
Most enzymes have an optimum pH at which they function. This usually depends upon
where in the body they are found.…read more

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Oxidoreductases these enzymes catalyse oxidation and reduction of hydrogen. An
example of an Oxidoreductases is succinate dehydrogenase.
Transferases these enzymes catalyse the transfer of a group from one compound to
another. An example of Transferases is aminotransferase.
Hydrolases these enzymes catalyse hydrolysis. An example of hydrolases is sucrase.
Lyases these enzymes catalyse the elimination of a group to form a double bond. An
example of lyases is citrate lyase.
Isomerases these enzymes catalyse intramolecular rearrangements. An example of
isomerases is phosphoglucose isomerase.…read more


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