Enzymes

Question 1

What is the transition state of a reaction?

Answer 1

High energy intermediate that lies between S and P

Question 2

What is the activation energy of a reaction?

Answer 2

Minimum energy S must have to allow reaction

Question 3

How can you increase the rate of a reaction?

Answer 3

Increase the number of molecule with activation energy
Increase chance of molecular collisions
E.g. Temperature, concentration and enzymes

Question 4

What is an enzyme?

Answer 4

Biological catalyst that increases the rate of a reaction by lowering the activation energy
Facilitates formation of the transition state

Question 5

What are some important features of enzymes?

Answer 5

Highly specific
Unchanged after the reaction 
Do not affect the reaction equillibrium 
Increase rate of reaction 
Proteins 
May require associated cofactors

Question 6

Why are we interested in enzymes?

Answer 6

Inheritable genetic disorders
Overactive enzymes can cause disease
Measurement of enzyme activity for diagnosis
Inhibition of enzymes by drugs

Question 7

What is the active site?

Answer 7

The place where substrates bind and where the chemical reaction occurs
Formed from amino acids at different parts of the primary sequence
Clefts or crevices
Have a complementary shale to substrate- lock and key
The active site forms a complementary shape after binding- induced fit
Bound by weak bonds

Question 8

How do enzymes work?

Answer 8

Substrate binds with enzyme active site to form enzyme substrate complex
Enzyme changes shape of substrate - ES transition
Product forms

Question 9

What happens if you increase the amount of substrate in a reaction?

Answer 9

Amount of product will increase until maximal amount of enzyme substrate complexes form

Question 10

What causes enzymes to denatures?

Answer 10

Temperature and pH

Question 11

What is the Michaelis-Menten model for enzyme catalysis?

Answer 11

A specific complex between the enzyme and the substrate is a necessary intermediate in catalysis
Not all enzymes obey this model

Question 12

What is vmax?

Answer 12

The maximal rate when all enzymes active sites are saturated with substrate

Question 13

What is km?

Answer 13

Substrate concentration that gives half maximal velocity

Question 14

What does a low km mean?

Answer 14

High affinity for substrate

Question 15

What does a high km mean?

Answer 15

Low affinity for substrate

Question 16

What is vmax measured in?

Answer 16

It is a rate so 1 unit is the amount of unit that converts 1 micromol of product per minute under standard conditions

Question 17

What is a lineweaver-Burke plot?

Answer 17

Allows for easy estimation of km and vmax

Question 18

What is an enzyme inhibitor?

Answer 18

Molecules that slow down or prevent enzyme reactions

Question 19

What is an irreversible enzyme inhibitor?

Answer 19

Binds very tightly
Generally convalent bond
E.g. Nerve gas

Question 20

What is a reversible enzyme inhibitor?

Answer 20

Not covalent so can dissociate freely e.g. Competitive- binds at active site
Non-competitive- binds at allosteric site

Question 21

What do competitive inhibitors affect?

Answer 21

Km

Question 22

What do non-competitive inhibitors affect?

Answer 22

Vmax

Question 23

What happens when you add more substrate when competitive inhibitor is present?

Answer 23

Will overcome effect of inhibitor so no effect on v max

But as competes for active site km increases

Question 24

Why does the non- competitive inhibitor lower vmax?

Answer 24

Decreased the turnover number of the enzyme