12

Question 1

What is the diffusion controlled unit

Answer 1

The upper limit of Kcat/km
- the rate at which enzyme and substrate diffuse together

Question 2

Absulote upper limit is

Answer 2

10^9s-1M-1
- anexymes about 10^8 are conc diehard to be perfect catalysis

Question 3

What is an inhibitor?

Answer 3

A compound that binds to an enzyme and reduces its acticity

Question 4

What are enzyme inhibitions important

Answer 4

• naturals inhibitors regulate metablioicsm
• many drugs, poisons and toxins are enzyme inhibitors
• used to study enzyme mechanisms
• used to study metablotic pathways

Question 5

Two classes of inhibitor

Answer 5

Irreversible inhibitor
Reversible inhibitor

Question 6

What is a irreversible in hibiritor ?

Answer 6

Binds covalantly to enzyme

Question 7

Reveersbale inhibirtr

Answer 7

Not coabvalently bound to the enzyme

Question 8

Reversible inhibitor can be either:

Answer 8

Competitive - binds at the active site, compères for site
Non competitive - doesn’t block substrate binding

Can be pure or mixed

Question 9

Features of irreversible inhibitor

Answer 9

• binds to enzyme and permetntly inactivarte a pool of enzyme
• inhibition reacts with a specific amino acid side chain, usually in the active site, and forms a covalent bond

Question 10

Features of reviewable inhibitor

Answer 10

• binds to enzyme but can also be released leaving enzyme in original conddiotn

Question 11

competitive inhibitor - mutually exclusives

Answer 11

• inhibitor competes diversely w the substrate for active site

Question 12

Kinetic parameters of competitive inhibition

Answer 12

• infinite [S] out competes inhibitor
• more substate needed to get V- Vmax/2

Question 13

Examples of competitive inhibitors

Answer 13

Transistor state analogues e.g Lipitor
Anastrozole (sold arimidex in NZ) - competitive inhibitor of the enzyme aromatise
- treatment for some breast cancers

Question 14

Non competitive einhibition features

Answer 14

• inhibitor binds at a different site then the substrate
• enzyme can bind to substrate or inhibitor or both
• changes how well enzyme can catalyse actual reaction - no matter much substrate you out in enzyme can bind fine, but enzyme can’t carry out reaction - Vmax reduces
• in pure non-competitive inhibition, the binding of I has no effect on binding of S ie the substrate binds to E and EI with the same affinity

Question 15

Pure non competitive inhibition

Answer 15

• binding changes the structures of the active site such that S still bonds, but the transition state stabilisation is no longer optimal

Question 16

Competitive vs pure non-competitive inhibition

Answer 16

Question 17

What is finer control

Answer 17

Turning an enzyme on and off

Question 18

Gycocgen phosporolyse is a

Answer 18

Dimer

Question 19

What is feedback and feed forward regulation needed for?

Answer 19

A sensible strategy is to avoid making unnecessary metabolic intermentiate

Question 20

Methods of enzyme regulation

Answer 20

• covalent modification e,g phosphorylation
• allosteric effects
• proteolytic cleavage
• turn gene expression on or off
• degrade the enzyme