2.4.8 enzyme inhibitors

Question 1

competitive inhibition

Answer 1

inhibitor molecule has similar shape to substrate & competes for active site of enzyme which blocks active site & prevents formation of ESCs

Question 2

inhibitor

Answer 2

substance which reduces/stops reaction

Question 3

non-competitive inhibition

Answer 3

competitor molecule attaches to part of enzyme but not active site which changes its shape so no longer complementary to substrate & prevents formation of ESCs

Question 4

name 3 types of inhibition

Answer 4

1. competitive inhibition
2. non-competitive inhibition
3. end-product inhibition

Question 5

describe competitive inhibitors

Answer 5

• fits into active site
• amount of inhibition relative to conc. of inhibitor/substrate molecules
• increasing substrate conc. ‘dilutes’ effect
• compete directly with substrate molecules
• form enzyme-inhibitor complex = catalytically inactive
• inhibitor isn’t changed
• reduces formation of ESCs & thus, product molecule formation
• reduces no. of free active sites
• usually reversible
• if binds irreversibly = called inactivator

Question 6

effect of more competitive inhibitor molecules

Answer 6

• more inhibitors collide with active sites & so effect of inhibition is greater

Question 7

describe non-competitive inhibitors

Answer 7

• don’t compete with substrate
• bind to enzyme at allosteric site = disrupts enzymes tertiary structure & changes it’s shape
• changes shape of active site so no longer complementary to substrate molecule = no ESCs can form
• increasing substrate conc. makes little difference
• some bind reversibly & some bind irreversibly

Question 8

what does end-product inhibition do

Answer 8

regulate enzyme-catalysed reactions
(eg. of negative feedback)

Question 9

describe process of end-product inhibition

Answer 9

1. product of 1 enzyme-catalysed reaction becomes the substrate for the next enzyme-catalysed reaction (in metabolic pathway)
2. changes shape of active site but is reversible - competitive/non-competitive inhibition
3. when conc. of product in cells fall, molecules detach from enzyme (1) & allow active site to resume normal shape

• multi-enzyme complexes increase efficiency of metabolic reactions without increasing substrate conc.