Lec 5 Enzymes Flashcards
what is an enzyme?
a biological catalyst that increases the rate of reaction by lowering the activation energy by providing an alternate reaction pathway where it stabilises the transition state
what are the key features of an enzyme?
highly specific proteins unchanged after the reaction does not affect the equilibrium increases rate of reaction some need co factors such as metal ions or co enzymes to work
why are we interested in enzymes?
they can be linked to inheritable diseases
overactive enzymes can cause disease
we use measurement of enzyme activity in diagnoses
inhibition of enzymes is a use of drugs
what is the active site ?
the place on the enzyme where the substrate binds and the reaction takes place.
it is only a small part if the enzyme, the rest is scaffolding , to bring the active site together through folding into the tertiary structure (active site formed from amino acids on different parts of the primary sequence)
How does an active site work?
induced fit hypothesis - the substrate and active site are complementary in shape, once the substrate binds to form the enzyme substrate complex , this causes a confirmational change in the enzyme, so the reaction can now go ahead, the product is release afterwards
substrates bind to enzymes non covalently allowing for release
what is Vo, why is it useful?
rate of reaction at time 0, this is useful as we know the substrate concentration at this point.
it gives the intial rate of reaction.
what are Vm and Km, how are they related?
draw graphs to represent this.
what equations do these graphs apply to.
we can draw a plot where reaction velocity vs substrate concentration, it forms a hyperbole
it is linked by the michales menesen equation
v0=(vmax*S)/km + S
this can be turned into a straght line equation to give a linewaever burke plot.
1/V0= Km/Vmax * 1/S + 1/Vmax
where the gradient is Km/vmax
y intercept is 1/vmax
x intercept is -1/km
define Vmax
theoretical maximal rate of reaction when all enzymes are saturated with substrate
define Km
the substrate concentration that gives half Vmax
what useful information does Km tell us?
it tells us the affinity of an enzyme for its substrate
a low km has a high affinity for its substrate
a high km has a low affinity for its substrate
what happens if we double the amount of enzyme?
we double the rate of reaction, as they are proportional
But NOT the standardised rate
what do you know about enzyme inhibitors?
they slow or prevent an enzyme reaction
the may be irreversible, which bind covalently, and permanently stop the enzyme from working
they are mainly reversible (no covalent and can freely dissociate) which have two types competitive and non competitive
how does competitive inhibition work?
binds at the active site, as it resembles the inhibitor, so it competes for the active site, this will INCREASE the value for Km but not the V max,
adding more substrate will overcome the inhibitor
how does non competitve inhibition work?
it will bind to another active site on the molecule , meaing the ES complex can no longer form, the enzyme no longer works.
this does not affect km
but LOWERS Vmax
Go over the group works and do maths examples
ya foo !!!!
