enzyme inhibitors

Question 1

state 4 ways in which multi-step reaction pathways can be regulated by cells

Answer 1

• competitive inhibition
• non-competitive inhibition
• end-product inhibition
• cofactors

Question 2

define enzyme inhibitor

Answer 2

molecule that prevents enzymes from carrying out normal function - reduce rate of reaction

Question 3

define competitive inhibitor

Answer 3

competes with substrate to bind to active site on an enzyme

Question 4

define non-competitive inhibitor

Answer 4

binds to an enzyme at an allosteric site
- does not compete with substrate

Question 5

define reversible inhibitor

Answer 5

can dissociate from the enzyme with ease
- most competitive inhibitors
- effect can be reversed (increase substrate concentration)

Question 6

define irreversible inhibitor

Answer 6

cannot dissociate from the enzyme - permanently disables the enzyme
- some competitive inhibitors, all non-competitive inhibitors

Question 7

explain how a competitive inhibitor affects the rate of an enzyme controlled reaction

Answer 7

• has similar shape to substrate so fits into active site
• blocks substrate from entering active site, preventing enzyme from catalysing
• substrate + inhibitor molecules compete to bind to active sites
• # of molecules binding to active site in given time reduced, rate of reaction slowed

Question 8

state 2 examples of competitive inhibitors and describe their actions

Answer 8

• statins: reduce production of cholesterol and conc. in blood
• aspirin: inhibits COX enzymes - prevents synthesis of chemical that produce pain + fever

Question 9

explain how a non-competitive inhibitor affects the rate of an enzyme-controlled reaction

Answer 9

• inhibitor binds allosteric site
• binding causes tertiary structure of enzyme to change, active site changes shape
• active site no longer has complementary shape so substrate is unable to bind to enzyme
• inhibitor does not compete with the substrate for the active site
• # of available active sites is reduced permanently, less molecules bind to them in given time, rate of reaction reduced

Question 10

state 2 examples of non-competitive inhibitors and describe their action

Answer 10

• organophosphates: inhibit acetylcholinesterase - leads to muscle cramps, paralysis or death
• proton pump inhibitors: block enzyme responsible for H+ secretion in stomach - prevents ulcers

Question 11

explain the effect of non-competitive inhibitors on the Vmax of an enzyme controlled reaction

Answer 11

permanently lower Vmax of a reaction, adding more substrate will not overcome effect of them

Question 12

explain the effect of competitive inhibitors on the Vmax of an enzyme controlled reaction

Answer 12

do not lower Vmax of a reaction, adding more substrate will result in more substrate than inhibitor and original Vmax will be reached

Question 13

define end-product inhibition

Answer 13

when product of a reaction inhibits the enzyme required for the reaction

Question 14

describe end-product inhibitions usefulness in controlling metabolic pathways

Answer 14

makes sure no excess products are made and resources are not wasted - negative feedback