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biology
biology module 2
biology chapter 4
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enzymes
are globular proteins that
catalyse
reactions in living organisms, they have an active site
how activation energy is lowered:
if two substrate molecules need to be joined the
enzyme
holds them together so they can
bond
more easily
if the ezyme is catalysing a breakdown, fitting into the active site puts a strain on the
bonds
of the
substrate
so they can be broken more easily
induced fit model:
active
site is not
complementary
active site is flexible, changes shape so substrate can bind to it
E-S complex forms
lock and key model:
active site is
complementary
active site is a
fixed shape
active site
doesn't wrap around substrate
factors affecting enzyme activity - temperature:
higher
temperature =
faster
rate of reaction
more
kinetic energy
for molecules so they move
faster
more frequent successful collisions between
active site
and
substrate
enzymes become
inactive
at low temperatures, and
denatured
at high temperatures
factors affecting enzyme activity - pH:
affects
ionic
and
hydrogen
bonds
protons interact with
polar
and
charged
amino acids
higher pH = increase in enzyme activity, until it reaches the
optimum
pH
factors affecting enzyme activity - substrate/enzyme concentration:
higher substrate concentration
increases
rate
higher enzyme concentration
increases
rate
factors affecting enzyme activity - enzyme concentration:
higher enzyme concentration
increases
rate as there are more
active
sites available
rate stops
increasing
when there is not enough
substrate
to occupy all the
active
sites
factors affecting enzyme activity - substrate concentration:
higher substrate concentration
increases
rate
the rate stops
increasing
when all the
active
sites are
occupied
competitive inhibition:
Ic have a
similar
structure to S (substrate)
Ic competes with S for the same
active
site
higher substrate concentration means that S can
out-compete
Ic and
restore
Vmax
non-competitive inhibition:
In binds to
allostenic
site
changes to
3D
structure of
active
site, the active site is no longer
complementary
to S
higher substrate concentration cannot restore
Vmax
equation for Q10:
A)
higher
B)
lower
2
cofactor
: a non-protein component that helps some enzymes carry out their function.
a coenzyme is an
organic
cofactor
coenzymes (organic cofactors):
participate in the
reaction
and are
changed
by it
they often act as
carriers
moving
chemical
groups between enzymes
they are continually
recycled
during the process
vitamins
are coenzymes
prosthetic groups:
a
cofactor
that is tightly bound to an enzyme
they are a
permanent
part of the enzyme's
active
site
competitive inhibitors:
similar
shape
to substrate
they bind to the
active
site but no
reaction
takes place, instead the active site is
blocked
non-competitive inhibitors:
the bind to a different site to the active site, called the
allosteric
site
causes the active site to change
shape
so that substrate molecules can
no longer fit
and bind to it
V-max: the enzyme's active sites are
saturated
, so the rate of reaction will not
increase
further
reversible inhibition
:
forms weaker hydrogen bonds or weak ionic bonds
the inhibitor can be removed
non-reversible inhibition:
forms
strong
covalent bonds
the
inhibitor
cannot be removed easily