1.1 Enzymes speed up chemical reactions
in the body, acting as a biological
catalyst. They catalyse METABOLIC
REACTIONS in the body, such as
digestion and respiration.
1.2 Enzyme reactions can be
INTRACELLULAR, within cells. Or
EXTRACELLULAR, outside cells, like
inside the blood or digestive system.
1.3 Enzymes are globular proteins which
have an active site, which has a
specific shape. The active site is the
part of the enzyme where the
SUBSTRATE molecules (The
substrate that the enzyme interacts
with) bind to. Enzymes are HIGHLY
SPECIFIC due to their 3D structure.
2 ACTIVATION ENERGY
2.1 In a chemical reaction a certain
amount of ENERGY is needed to be
supplied to the chemicals before the
reaction can start, this is called the
ACTIVATION ENERGY. It is often
provided as heat. Enzymes (Catalysts
in general also) lower the amount of
activation energy required, meaning
reactions not only happen at a lower
temperature but also increases the
rate of reactions.
2.2 When a substrate fits into the
enzymes ACTIVE SITE, it forms a
This is what lowers the activation
energy. Two reasons why:
2.2.1 1) If the two substrate molecules need to be
JOINED together then the enzyme's active sit
will hold them close together so reducing any
repulsion between the molecules, allowing
them to bond more easily.
2.2.2 2) If the enzymes is catalysing a
BREAKDOWN reaction then fiiting the
substrate into the active site allows the enzyme
to put a strain on the bonds, so the substrate
molecules break up more easily.
3 MODELS OF FIT
3.1 The LOCK AND KEY MODEL, is the
idea that the enzymes only work with
specific substrates which will fit into
their active site. Early scientists came
up with the idea of the lock and key
model, where the substrate fits into the
active site in the same way that key fits
into a lock. However this was soon
dismissed as the enzyme and substrate
did not have to exactly fit into
eachother. The enzyme substrate
complex could change shape slightly.
3.2 The INDUCED FIT MODEL explains
why enzymes are so specific and only
form a bond to one specific substrate.
The substrate doesn't only have to be
the right shape, it also has to change
the active site's shape in the correct
4 ENZYME SPECIFICITY
4.1 Due to their 3D structure enzymes are
very specific and they usually only
catalyse one reaction, for example
maltase only breaks down maltose.
This is because only one substrate will
fit in the active site. The active site itself
is determined by the enzymes 3D
structure, which in turn is determind by
its own primary structure.
4.2 Each different enzyme has a different
3D structure so a different active site
shape. If the substrate does not fit into
the active site then the reaction
cannot be catalysed. Also if the 3D
Structure is altered in any way, as will
be the active site, this would mean
that the substrate would no longer fit,
so the enzyme will be unable to carry
out its function.
5 ENZYME CONCENTRATION
5.1 The more enzyme molecules that
there are in a solution then the more
likely a substrate molecule is to collide
with one and form and enzyme
substrate complex. So increasing the
rate of reaction. However if the amount
of substrate is limited there comes a
point where there is more than enough
enzymes and adding more would have
no further effect.
5.2 One possible question is how to
inestigate the effect of enzyme
concentration on the initial rate of a
reaction. This would be measured by
showing HYDROGEN PEROXIDE
being broken down into water and
oxygen by the enzyme CATALYSE.