Biology Gcse Enzymes

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  • Created on: 06-04-13 07:56
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CIE IGCSE Biology: Enzymes
Catalyst: a substance that speeds up a chemical reaction and is not changed by the reaction.
Enzymes: proteins that function as biological catalysts.
The enzyme action:
1. The substrate molecule fits onto the active site of the enzyme.
2. The substrate molecule has a specific shape which fits only onto the active site of a specific enzyme in a lock and
key model in which the active site is the lock and the substrate is the key.
3. The substrate molecule is brought closer together and broken down / build up (depends on the type of reaction)
forming a new product.
4. The enzyme is not changed and is reused.
The effect of changes in temperature and pH on enzyme activity
At a very low temperature, the enzyme molecules and the substrate molecules
are moving very slowly. As the temperature increases, their kinetic energy
increases and they move faster. The higher the temperature, the faster they
move around, and the more frequently they collide with each other. When they
have more energy when they collide, it's easier for the reaction to take place.
So as the temperature rises, the rate of reaction also increases. However, at a
very high temperature, the reaction starts to slow down because the enzyme
molecules are beginning to denature. They lose their shape and the substrate no
longer fits into the active site. In an extremely high temperature, the enzyme
molecules are completely denatured so no reaction takes place. The
temperature the enzymes work the best at is called the optimum temperature.
Most enzymes in the human body have an optimum temperature around 37°C while most enzymes in plants have an
optimum temperature of around 25°C.
At a very low or high pH, the enzyme molecules lose their shape so their substrate
cannot fit into their active site. For example, pepsin is a proteindigesting enzyme

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CIE IGCSE Biology: Enzymes
(protease) that works in the stomach at a very low pH ­ pH2 which is why the stomach secretes hydrochloric acid.
Amylase works best at pH 7 or slightly above and is found in the mouth.
Germination of Seeds
1. The seed contains the following enzymes: amylase, maltase, lipase, and protease.
Amylase breaks down starch in the seed into maltose. Maltose breaks down maltose into glucose.
Glucose is then used in respiration to release energy.…read more

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CIE IGCSE Biology: Enzymes
The use of microorganisms and fermenters to manufacture the antibiotic penicillin and enzymes
for use in biological washing powders:
In a fermenter, the microorganism grows in a liquid called the medium. The medium must contain everything that the
microorganism needs to live and produce the desired product.…read more

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CIE IGCSE Biology: Enzymes
3. Bacteria provided with oxygen for aerobic respiration
4. Optimum temperature (26°C) and optimum pH 56 are set
5. The mixture is stirred to prevent settling
6. Bacteria grow and reproduce rapidly
7.…read more


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