Unit 4 - Enzymes

Question 1

What is an enzyme?

Answer 1

Biological catalyst

Question 2

What is the role of enzymes?

Answer 2

To speed up chemical reactions

Question 3

What are virtually all enzymes made of?

Answer 3

Proteins

Question 4

What do most enzymes have associated with them?

Answer 4

Co-factors

Question 5

What is the difference between enzymes and chemical catalysts?

Answer 5

Enzymes are very specific in the substrates that they will use
- active site only accepts certain molecules
Chemical catalysts are not specific

Question 6

How can inhibition of an enzyme be used to halt a particular reaction?

Answer 6

Interferes with a metabolic process

- can be used to treat a disease or infection

Question 7

Give an example of how inhibition of a human enzyme can be used to treat a metabolic disease

Answer 7

Inhibition of angiotensin converting enzyme (ACE) can be used to treat high blood pressure

Question 8

Give an example of how inhibition of a pathogen enzyme can be used to treat an infection

Answer 8

Inhibition of bacterial cell wall enzyme can be used to treat bacterial infections

Question 9

What factors are important in a drug?

Answer 9

Toxicity
- inhibition of related enzymes or enzymes involved in other processes
Bioavailability
Penetration across membranes
Clearance from the body
- low half life
Non-specific binding to other macromolecules
Degredation
- e.g. by the liver

Question 10

What are the six major types of enzyme classification?

Answer 10

Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases

Question 11

What are the two types of enzyme inhibition?

Answer 11

Reversible

Irreversible

Question 12

Describe reversible inhibition of enzymes

Answer 12

Rapid dissociation of the enzyme-inhibitor complex when the inhibitor is removed

Question 13

Describe irreversible inhibition of enzymes

Answer 13

Very slow dissociation of the enzyme-inhibitor complex

- often there is covalent attachment of the inhibitor to the enzyme

Question 14

What types of reversible inhibition are there?

Answer 14

Competitive inhibition
- most common
- direct competition
Non-competitive inhibition
- binds at different site
- rare
Uncompetitive inhibition
- very rare!

Question 15

Describe competitive inhibition

Answer 15

The inhibitor almost always binds to the same active site as the substrate
The enzyme can bind the inhibitor or the substrate but not both at the same time
- competitive!
Usually the inhibitor is closely related to the substrate
- structurally

Question 16

How can competitive inhibition be overcome?

Answer 16

Increasing concentration of substrate

- related to how tightly bound the enzyme-substrate complex is

Question 17

What is plotted to determine important kinetic data from easily measurable parameters?

Answer 17

Lineweaver-Burk plot

Question 18

What effect does a competitive inhibitor have on a Lineweaver-Burk plot?

Answer 18

The steepness of the line increases relative to the control
Vmax remains unchanged
Km is increased

Question 19

What effect does increasing concentration of substrate have on non-competitive inhibition?

Answer 19

No effect

Question 20

What is allosteric inhibition?

Answer 20

Binding of inhibitor at site other than the enzyme active site

Question 21

What does binding of an inhibitor at an allosteric site cause?

Answer 21

Conformational change to enzyme reducing binding between enzyme and substrate

Question 22

Give an example of an allosteric inhibitor

Answer 22

Non-nucleoside Reverse Transcriptase Inhibitors for HIV Infection

Question 23

What is a reverse transcriptase enzyme?

Answer 23

Replicative enzyme of HIV

- converts viral RNA to double stranded DNA

Question 24

What effect does a non-competitive inhibitor have on a Lineweaver-Burk plot?

Answer 24

As non-competitive inhibitor concentration against a control experiment show an increase in gradient compared to with the origin at the x-axis intercept
Increased Y intercept same x axis point

Vmax is reduced
Km remains the same as no affect on affinity

Question 25

What is uncompetitive inhibition?

Answer 25

Inhibitor binds to the enzyme substrate complex but not to the enzyme