Enzymes



You should know the following points
Define enzymes as proteins which functions asbiological catalysts.
Explain enzyme action in terms of the "lock and key hypothesis".
investigate and describe the effect of temperature and of pH on enzyme activity.































 

 

 

 

 

 



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Speed in chemical reactions can be very important. Think of what would happen if the food you just ate takes 3 days to digest.

There are chemicals (or substances) that can change the speed of chemical reactions. These are known as catalysts.

Important properties of catalysts are:
         - Only a small amount is needed change the speed of reactions.
         - They remain unchanged at the end of the reaction. They are "reusable".

Enzymes are biological catalysts that changes the speed of chemical reactions without themselves being changed at the end of the reaction.

Properties of Enzymes:
- Enzymes are made of proteins.

- They speed up chemical reactions inside the cytoplasm.

- They are needed only in small amounts. They remain unchanged after each reaction and can therefore
   be reused.

- Each enzyme can only work on one chemical reaction. For example, catalase will only work on hydrogen
  peroxide (to form water and oxygen). They are highly specific. Substrate is the chemical that the
  enzyme is working on.

- They are affected by temperature.

- They are affected by pH.

Therefore, how fast the enzyme can catalyze or work on the chemical reaction depends on factors like temperature and pH.

Effect of Temperature on Enzyme
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- At very low temperatures, enzymes are inactive.
- The activity of enzymes increases when the temperature increases (and therefore the reactions that
  they work on, or catalyze, will also become faster).
- Each enzyme has a special temperature that they are most active. This is the optimum temperature
  for that enzyme. Each enzyme has it’s own optimum temperature.
- When the temperature is too high, the enzymes are destroyed, or denatured.

Effect of pH on Enzyme
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- Different enzymes work best at different pH. You will understand this better in “Nutrition –
  digestion”.
- The pH that makes the enzyme most active is known as the optimum pH.
- If the pH is very high or very low, enzymes can be denatured.

Therefore, how fast the enzyme can catalyse depends on factors like temperature or pH. 2 other factors that affect the speed of enzyme reactions are:
     - Concentration of substrate
              - when substrate concentration increases, the speed of reaction increases.
     - Concentration of enzymes
              - the higher the concentration of enzyme, the faster the speed of reaction.

How Enzymes Work
The enzymes work has been explained using the "lock and key hypothesis".

lock and key.bmp (1082934 bytes)

Check out this site:
http://www.bbc.co.uk/schools/gcsebitesize/biology/humans/enzymesrev1.shtml

This topic is a favourite in practical exams. You are frequently asked to investigate the effect of temperature and pH on the speed of enzyme activity. This topic may also be asked together with nutrition.

Design a mind map to summerise the properties and nature of enzymes.

Think about this:
If you increase the concentration of substrate, the speed of enzyme reaction will increase. But, there will come a time when any more increase in the substrate concentration will not increase the speed of reaction.
WHY?

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