AQA AS Biology Unit 1- enzymes

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They are GLOBULAR PROTEINS that act as catalysts. Catalysts alter the rate of
chemical reaction without undergoing permanent changes themselves. They are not
used up in the reaction, so it can be REUSED and they are effective in very small
amounts. They do not make reactions happen, just speeds up the reaction
Molecules must collide with sufficient energy to alter the arrangement of their
atoms to form the products
The energy of the products must be less than that of the substrates
Initial boost of energy id needed to start the reaction.
The minimum amount of energy needed to activate the reaction is called activation
Enzymes work by lowering this activation energy. In this way enzymes allow reactions
to take place at a lower temperature than normal. This enables some metabolic process
to occur rapidly at the human body temperature of 37 degree Celsius. Without
enzymes these reactions will take longer time
Enzyme structure
They have a specific 3-D shape (tertiary structure) that is the result of their sequence
of amino acids (primary protein structure)

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The molecule on which the enzyme acts is called SUBSTRATE. This fits neatly into
active site to form an enzyme-substrate complex. This is held together by temporary
bonds formed between certain amino acids of the active site and groups on the
substrate molecule.
Changing certain amino acids that are not part of the active site also prevent the
enzyme from functioning because changed amino acid may be one that forms hydrogen
bonds with other amino acids.…read more

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H ON ENZYME ACTION- pH is a measure of hydrogen ion
concentration. Each enzyme has an optimum pH at which it works fastest and it
depends on where it is. For e.g. salivary amylase has an optimum pH of 7.
A change in pH alters the shape of the enzyme and active site because changes in
pH can cause the bonds that maintain the tertiary structure of the enzymes to
break. So enzymes are no longer complementary. The enzyme has been denatured.…read more

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INHIBITORS - Inhibitors slow the rate of reaction
Inhibitors interfere with the functioning of the active site and so it reduces its
They can be;
INHIBITORS-which binds to the active site of the enzyme
They have a molecular shape similar to that of the substrate. This allows them to
occupy the active site of an enzyme. Therefore they compete with substrate for
the active sites.…read more

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Commercial use of enzymes
Biological washing powder- it contains enzymes that remove stains.
The enzymes are coated with a special wax that melts in the wash, releasing the
enzymes.…read more


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