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Preview of Enzymes

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Chemical Reactions
Chemical reactions can only take place when different particles collide with enough energy to react.
The minimum amount of energy particles must have to be able to react is known as the activation
Many chemical reactions take place in living cells. These have to be carried out at particular rates
otherwise life could not be sustained. Reactions in living cells need catalysts.
These are special chemicals which increase the rate of chemical reactions.
They are not used up in the reaction so they can be used over and over again.
Different types of reaction need different catalysts.
They work by bringing reacting particles together and lowering the activation energy needed for them to
These biological catalysts are called enzymes:
Enzymes catalyse many different reactions. These include:
- Building up large molecules from smaller ones ­ e.g. protein synthesis and photosynthesis.
- Breaking down large molecules into smaller ones ­ e.g. respiration and digestion.
- Changing one molecule into another.
Structure of an Enzyme
Enzymes are large protein molecules made up of long chains
of amino acids.
These long chains are folded and coiled to produce a specific
shape which enables other molecules to fit into the enzyme.
This part of the enzyme is called the active site.
Enzymes will only react with a specific substrate. The active
site is complementary in shape to the substrate molecule.
Enzymes are not changed when they perform their function.
An enzyme can therefore be used over and over again.
Mechanism of Enzyme Action
The Effect of Temperature and pH
on Enzymes
Changing the temperature
changes the rate of an
enzymecatalysed reaction.
Like with any other reaction, a
higher temperature increases the rate
at first. But if it gets too hot, some of
the bonds holding the enzyme

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This destroys the enzyme's special shape and so it won't work any more. This
means it has denatured.
Enzymes in the human body normally work best at around 37°C ­ body temperature.
The pH also affects enzymes. If it's too high or too low, the pH
interferes with the bonds holding the enzyme together. This
changes the shape and denatures the enzyme.
All enzymes have an optimum pH that they work best at. It's
often neutral pH 7, but not always ­ e.g.…read more

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- Bile is produced in the liver. It's stored in the gall bladder before it's releasing into the small intestine.
- The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to
work properly. Bile is alkaline ­ it neutralises the acid and makes conditions alkaline. The enzymes
in the small intestine work best in these alkaline conditions.
- It emulsifies fats. In other words in breaks the fat into tiny droplets.…read more

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Uses of Enzymes
Enzyme Use
Protease Used to predigest proteins during the manufacture of baby foods.
Used together with protease in biological detergents to break down digest the
substances in stains into smaller, water soluble substances.
Used to convert starch syrup, which is relatively cheap, into sugar syrup, which is more
valuable for example, as an ingredient in sports drinks.…read more


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