enzymes 2

Question 1

pre steady state

Answer 1

with excess substrates, for a few hundred
milliseconds product formation gradually
builds up

Question 2

steady state

Answer 2

reaction rate and intermediate concentration change relatively slowly

Question 3

initial rate

Answer 3

V0

varies hyperbolically with substrate concentration for a fixed enzyme concentration

Question 4

Michaelis-menten equation

Answer 4

vo = Vmax [S] / Km + [S
applies to simple enzyme

relies on assumptions: number of molecules is large
equation relates initial velocity to concentration of substrate, and two parameters, Km & Vmax

Question 5

high concentrations ([S]» Km )

Answer 5

all active sites are used
Reaction rate is independent of [substrate]
No more enzyme-substrate complex can be formed
0 order/saturation kinetics

Question 6

km

Answer 6

vmax/2
Enzyme velocity is most sensitive to changes
in substrate concentration just below Km
- Knowing Km permits calculation of [substrate]
required to saturate all active sites
Low Km = high substrate affinity
High Km = low substrate affinity

Question 7

low concentrations ([S]&laquo_space;Km ),

Answer 7

active site occupancy is low
Reaction rates is directly related to number of site occupied
- 1st order kinetics (rate is proportional to [substrate])

Question 8

Maximum Catalytic Efficiency

Answer 8

for substrate to be converted to product, substrate and enzyme molecules must collide
some enzymes have evolved to maximum catalytic activity random diffusion
organised assemblies can breach this rule

Question 9

inhibitors

Answer 9

can affect enzyme activity by binding to the active site
decrease reaction velocity and in time the affinity with substrates

• insight into catalytic mechanisms
• insight into metabolic control
• permits synthesis of inhibitors as therapeutic agents

Question 10

inhibitor not covalently bound

Answer 10

reversible inhibitor

can be removed by dialysis

Question 11

competitive inhibition

Answer 11

Competes with substrate at substrate recognition site
increase the km as you need more substrate to get started but don’t change Vmax
can be overcome by increasing substrate

Question 12

non-competitive inhibitoror

Answer 12

doesn’t compete for binding site
lowers enzymes v max as it lowers active enzyme but does not affect km
reduces active sites

Question 13

uncompetitive reversible inhibitor

Answer 13

can only bind to the enzyme-substrate complex (ES) and not to free enzyme
it needs to bind at a site created by conformational change or to the substrates itself
can not be overcome by substrate concentration

Question 14

Irreversible Inhibition

Answer 14

inhibitors bind via covalent bonds to enzyme
cannot be removed by dialysis
reduces the amount of enzymes available for reaction
can target functional group or metal atom of active site

Question 15

suicide inhibitors

Answer 15

unreactive until they bind to the active site of the enzyme and then combines irreversibly stopping it from doing it’s job
good for specialisation because it doesn’t react until binded

Question 16

comparing isozymes

Answer 16

different kinetic parameters: they have different roles so they need different parameters

Question 17

substrate inhibition

Answer 17

substrate of enzymes act as uncompetitive inhibitors: very high substrate concentrations binds to second non-catalytic site

Question 18

product inhibition

Answer 18

end-product of an enzymatic pathway may affect activity