enzymes 2

Question 1

how to measure enzyme activity?

Answer 1

1-electrophoresis: place different samples labelled into a well and apply current. see how much they move- depends on electrical activity
2-measure activity in a sample- can be difficult when more than one enzyme carry out the same function

Question 2

how do enzymes which have more than one substrate work?

Answer 2

they tend to transfer one group to another.
1-random order
2- ordered First add S1, then add S2. first two steps are reversible.
E+S1–> ES1–> ES1ES2–> E + S1+ S2
3-ping-pong displacements- substrates bounce on and off the enzyme. all steps reversible except for last. product 1 bounces off,substrate 2 bounces on.
E+S1–> ES1–>EP1–>ES2–>E+P2

Question 3

allosteric enzymes

Answer 3

have multiple sub-units with many active sites
when substrate binds to one active site, it can change the shape of other active sites making it easier for other molecules to attach- COOPERATIVE BINDING

Question 4

What affects enzyme activity?

Answer 4

1- Temperature (increases collisions, internal energy, can denature)
2-Ph (affects charge, can denature)
3-competitors

Question 5

competitive inhibitors

Answer 5

1-compete with substrate for active site
2- If high substrate concentration is added, it can overcome the effect of the competitor
3-Km will increase-affinity decreases
4-Vmax will stay the same

Question 6

non-competitive inhibitors

Answer 6

1- will bind to site on enzyme which will alter shape of active site
2- Km will stay the same as active site is still free
3-Vmax will decrease as shape of active site is altered so may take more time to bind

Question 7

uncompetitive inhibitors

Answer 7

binds to site near active site when substrate is bound- prevents substrate from detaching

Question 8

how to control enzyme activity?

Answer 8

feedback inhibition: enzymes usually involved in metabolic pathways so inhibiting the function of one enzyme will inhibit the rest. so build up of one products slows down reaction pathway
BY:
1-allosteric control: binding of competitor to site which is not active site. this alters shape of active site so substrate can no longer bind.
2- covalent modification: phosphorylation at single or multiple sites.
3-proteolytic cleavage: proproteins/enzymes= inactive precursor protein are cleaved to give active enzymes by proteases. e.g. digestive enzymes and insulin.