Enzymes Summary

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The chemical reactions within an organism
represent its metabolism. Each metabolic
reaction involves a substrate being
converted to a product and is catalysed by an enzyme.
Catalysts speed up the rate of reaction by lowering the activation energy needed for
the reaction to occur.
Enzymes are globular proteins with a specific tertiary shape, part of which forms an
active site.
A substrate binds with the active site to form an enzymesubstrate complex. Products
are formed at the active site. The products are released from the enzyme molecules,
which are unaltered.
There are two models of enzyme action the lock and key hypothesis and the induced
fit hypothesis The lock and key hypothesis explains enzyme specificity, due to the
complementary shape of the substrate and the enzyme's active site. The induced fit
hypothesis suggests that binding of the substrate induces a change in enzyme
structure which, through putting the substrate molecule under tension, explains why
activation energy is lowered in catabolic reactions.
Factors that increase the rate at which substrate and enzyme molecules might collide
will increase the rate of reaction and include temperature, substrate concentration
and enzyme concentration.
Factors that affect the tertiary structure of the enzyme will have an adverse effect on
the enzyme action by preventing binding of the substrate and include high
temperature, and pH changes away from the optimum.
Cofactors are nonprotein substances that are necessary for the action of some
enzymes. Cofactors can be ions or organic molecules (coenzymes).
Inhibitors are substances that reduce the activity of enzymes competitive inhibitors
mimic the substrate and compete with it for the enzymes active site, the extent of the
inhibition depends on the relative proportion of substrate and inhibitor molecules.
Noncompetitive inhibitors tend to stop enzyme activity and act in different ways.
Enzymes can be immobilised in a variety of ways and provide many advantages for
their commercial use.


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