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  • Created by: Leavers14
  • Created on: 08-04-14 19:10


Enzymes are catalysts produced by living things

A catalyst is a substance which increases the speed of a reaction, without being changed or used up in the reaction. 

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Enzymes have special shapes

Chemical reactions usually involve things either being split apart or joining together

Every enzyme has a unique shape that fits into the substance involved in the reaction.

Enzymes are really picky- they usually catalyse only one reaction

For the enzyme to work, the substance has to fit its special shape. If the substance doesn't match the enzyme's shape, then the reaction will not be catalysed.  

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Optimum Temperature and pH for enzymes

Changing the temperature changes the rate of an enzyme-catalysed reaction. 

A higher temperature increases the rate at first. But if it gets too hot, some of the bonds holding the enzyme together break. This destroys the enzyme's special shape and so it won't work anymore. This means that the enzyme is denatured

Enzymes in the human body work best at around 37 degrees celsius.

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. pepsin is an enzyme used to break down proteins in the stomach. It works best at pH 2, which means it's well-suited to the acidic conditions in the stomach. 

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Enzymes and digestion- Amylase

Amylase converts starch into sugars. Amylase is made in three places:

1). The salivary glands

2). The pancreas

3). The small intestine 

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Enzymes and digestion- Protease

Protease converts proteins into amino acids

Protease is made in three places:

1). The stomach (it's called pepsin there)

2). The pancreas 

3). The small intestine 

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Enzymes and digestion- Lipase

Lipase converts lipids into glycerol and fatty acids 

Lipase is made in two places:

1). The pancreas

2). The small intestine 


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Bile neutralises the stomach acid and emulsifies fats 

Bile is produced in the liver. It's stored in the gall bladder before it's released 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 the conditions alkaline. The enzymes in the small intestine work best in these alkline conditions. 

It emulsifies fats. In other words it breaks the fat into tiny droplets. This gives a much bigger surface area of fat for the enzyme lipase to work on- which makes its digestion faster

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