SARAH CHARLTON’S
SLIDE SHOW!
Biological processes are regulated by the action of enzymes. Enzymes as
proteins that act as catalysts. The importance of enzymes is lowering
activation energy so that the chemical reactions necessary to support life
can proceed sufficiently quickly and within an acceptable temperature
range. The mode of action of enzymes in terms of the formation of an
enzyme - substrate complex.
The way enzymes work can also be shown by considering the energy
changes that take place during a chemical reaction. We shall consider a
reaction where the product has a lower energy than the substrate, so the
substrate turns into the product. Before it can change into the product,
the substrate must overcome an “energy barrier” called the activation
energy (EA).
In a chemical reaction
the larger the activation
energy, the slower the
reaction will be because
only a few substrate
molecules will by
chance have sufficient
energy to overcome the
activation energy
barrier.
When you are calculating
activation energy it is useful to
know how much energy is in the
product and how much is in the
reaction. The graph will then
show you how it’s distributed.
Most physiological
reactions have the
largest activation
energies, so they
simply don’t happen
on a useful time
scale.
The activation energy of a chemical reaction is actually the energy
required to form the transition state, so enzymes lower the activation
energy by stabilizing the transition state, an they do this by changing the
conditions within the active site of the enzyme.
As you can see from
this diagram the
activation energy has
been lowered by
enzymes and this has
stabilized the
transition state to a
peak, the energy
barrier has been
broken.
When changing the conditions you can not lower the activation energy.
However, enzymes seem to lower the activation energy of a reaction because
they split the reaction into stages, each with a lower activation energy. The
cells in the product supply this much small amount of energy from ATP which
was produced in respiration from the enzymes. This allows many reactions to
take place easily at the temperatures that normally occur in the body of an
organism.
Enzymes are biological catalysts in the human body also enzymes are proteins.
Proteins are important compounds in living organisms - not just enzymes but
in other ways. There are about 40,000 enzymes in a human cell each
controlling a different chemical reaction. They increase the rate of reaction
but decrease activation energy as it’s a barrier for the enzymes. Enzymes make
it possible for chemical reactions to take place at normal temperatures. The
temperature in the human body is about 350c. If the activation energy is high
the enzyme reactions will be slower and the body will feel this, this is why the
enzymes lower the activation levels otherwise the body temperature will drop.
This is how a
substrate fits
onto an enzyme
in a reaction.
As you know the activation energy for many necessary
biological reactions is simply too high for these
reactions to proceed, however these reactions are vital
to the life of an organism. Enzymes will therefore
lower the activation energy barrier and allow these
reactions to occur.
It’s a key
idea.
Enzyme molecules have a complex tertiary structure. The substrate molecules of the
enzyme must be precisely the right shape to fit it into part of the molecule called the
active site. The substrate molecules are attracted to the active site and form an
enzyme - substrate complex. This complex only exists for a fraction of a second, this
is when the products of the reaction form. The activation energy is low in this
reaction because it is controlled by enzymes and little energy is needed to bring the
two substrate molecules together.
This is a diagram to
show an enzyme in
action.
THIS IS THE END OF MY
SLIDE SHOW.
HOPE YOU ENJOYED IT
AND LEARNT A LOT!