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Summary Biological Molecules - Enzymes
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Biological Molecules - Enzymes
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EnzymesEnzymes are biological catalysts.
They catalyse metabolic reactions at a cellular level and as a whole.
They can affect the structure of an organism (production of collagen) and functions
(respiration).
Enzyme action can be intracellular (within cells) and extra cellular (outside cells).
They are proteins.
They have an active site which is a specific shape so that a specific substrate can bind to
it.
They are highly specific due to their tertiary structure.
Enzymes lower the activation energy of a reaction allowing a reaction to occur at a lower
temperature. This occurs because when an substrate fits into an enzymes active site it forms an
enzyme-substrate complex which lowers the activation energy due to:
If two substrate molecules need to be joined being attached to an enzyme holds them
closer together reducing repulsion so they can bond more easily.
If an enzyme is catalysing a breakdown reaction, fitting into an active site puts strain on
the bonds in the substrate so it can break down more easily.
The lock and key model was replaced by the induced fit model as it helps to explain why
enzymes are so specific and only bond to one particular substrate - it demonstrates that the
substrate doesn't just have to be the right fit but it also has to somewhat make the active site
change shape.
Enzyme properties relate to their tertiary structure:
Enzymes are very specific as they only catalyse one reaction as only one complementary
substrate would fit into it. The active site of an enzyme is determined by the enzymes tertiary
structure which is determined by the primary structure. The primary structure is determined by
a gene therefore if the order of bases changes or there is a mutation the tertiary structure also
changes (temperature, pH). The primary structure affects the secondary structure as if the
sequence of amino acids changes then the hydrogen bonding in the secondary structure which
determines the alpha helix shape and the beta pleated sheet would also change. This would
mean that for the tertiary structure the 3D shape would not be specific. If the tertiary structure
is altered in anyway the shape of the active site changes so the substrate will no longer fit into
it and the enzyme-substrate complex will not be formed.
Enzyme activity is affected by:
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