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WJEC AS Biology
BY1 Topic 1.4…read more

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Enzyme Structure
· Tertiary globular proteins where protein chain is
folded back on itself into a spherical/ globular
· Each enzyme has its own sequence of amino
acids, held in tertiary form by hydrogen bonds,
disulphide bridges and ionic bonds
· Complex 3D shape gives enzyme many of its
· Although enzyme molecule is large, only a small
region ­ the active site ­ is functional…read more

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Grade Boosters
· In cells metabolic reactions take place quickly,
thousands of reactions are taking place
simultaneously. Order and control are essential if
reactions are not to interfere with each other ­ made
possible by action of enzymes
· Induced fit model of enzyme action ­ a modified
version of lock and key hypothesis. Proposes that the
enzyme changes it's shape slightly to accommodate
the substrate. As enzyme changes it's shape it places a
strain on the substrate molecule and distorts a
particular bond. This lowers the activation energy
needed to break the bond.…read more

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How enzymes work
Enzymes are biological catalysts that speed up
the rate of metabolic reactions
· Reactions where larger molecules get broken
down into smaller molecules
· Where smaller molecules are built up into
larger, complex molecules
Enzyme + substrate = Enzyme-substrate complex = Enzyme + product…read more

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Properties of Enzymes
· Specific ­ each enzyme will catalyse only one
particular reaction (sucrase sugar, sucrose)
· Very efficient, high turnover number- they can
convert many molecules of substrate per unit of
· Lowers activation energies ­ Chemical reactions
need energy to start them off (activation energy).
In the body, enzymes lower the activation energy
of a reaction and so reduces the input of energy
required allowing reactions to take place at lower
temperatures…read more

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Effect of temperature
· Increase in temp molecules
have greater kinetic energy
· Increases chances of collision,
increasing rate of reaction.
· Until an optimum (for most
enzymes approx 40C)
· Above optimum temp. Increasing
vibration of molecules causes
hydrogen bonds to break, causing
a change in tertiary structure and
active site is altered, so that
substrate no longer fits. It is said
to be denatured.
-This is a permanent change.
· If subjected to low temps,
(freezing) enzyme = inactivated,
only worrking again if temp is
raised…read more

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