Enzyme inhibition

Question 1

Two main categories/classes of inhibitors

Answer 1

Irreversibel
Reversible

Question 2

Definition of inhibitors

Answer 2

Molecules that interfere with catalysis, slowing or halting enzymatic reactions

Question 3

3 types of reversible inhibitors

Answer 3

Competitive
Uncompetitive
Noncompetitive

Question 4

Difference between uncompetitive and noncompetitive inhibition

Answer 4

Uncompetitive binds only when the substrate is bound and it binds to additional binding site on active site
Noncompetitive binds only to allosteric site and in all conditions (so when substrate is bound and when it is not)

Question 5

When does the uncompetitive inhibitor bind?

Answer 5

Only after substrate is bound

Question 6

When does the noncompetitive inhibitor bind?

Answer 6

In all conditions, substrat bound or not bound

Question 7

What does sulphanilamide mimic the structure of? and thus inhibits the metabolisation of

Answer 7

PABA (p-aminobenzoic acid)

Question 8

How is the rate of reaction effected by the inhibitor?

Answer 8

The rate decreases
Due to decrease in affinity
More substrate is needed

Question 9

What is Km?

Answer 9

Substrate concentration at half Vmax

Question 10

What happens to the Vmax during competitive inhibition?

Answer 10

Nothing
It is not changing because as substrate increases inhibition decreases eventually to the point where it disappears

Question 11

What happens to the Km during competitive inhibition?

Answer 11

Increases

Question 12

Does competitive inhibition affect catalysis?

Answer 12

No, does not effect the catalysis and the process

Question 13

With competitive inhibitors how do the Vmax compare to reaction with no inhibitor?

Answer 13

They are the same

Question 14

In a noncompetitive inhibitor how is the Km effected?

Answer 14

No change
Because the binding site is the same and the binding is the same (affinity for binding is the same)

Question 15

In a noncompetitive inhibitor how is the Vmax effected?

Answer 15

Decrease
Activity of enzyme is decreased

Question 16

What does the noncompetitive inhibitor affect? The affinity to bind or the enzymatic activity?

Answer 16

Enzymatic activity

Question 17

Can a change in conformation cause and enzyme to have affinity for a different substrate?

Answer 17

Yes

Question 18

Which inhibitor can be used to map an active site?

Answer 18

Irreversible inhibitor
Affinity labels

Question 19

3 major types of irreversible inhibitors

Answer 19

Group specific reagents
Affinity labels (or reactive substrate analogs)
Suicide inhibitors (or mechanism-based inhibitors)

Question 20

Why is it group specific reagents irreversible inhibition?

Answer 20

Only interacts with one specific amino acid in a specific position in the compound (the ex serine of the active site)

Question 21

How does the affinity labelling irreversible inhibitor work?

Answer 21

Part of inhibitors attaches to part of the enzyme

Question 22

How does the suicide irreversible inhibitor work?

Answer 22

Binds as a substrate and is then modified by enzyme into an irreversible inhibitor

Question 23

What kind of inhibitor is penicillin?

Answer 23

Suicide irreversibel inhibitor

Question 24

What are transition state inhibitors?

Answer 24

Inhibitor that resembles the transition state substrate

Question 25

What are enzyme inhibitors?

Answer 25

Compounds that decrease an enzyme’s activity

Question 26

What are competitive inhibitors?

Answer 26

Inhibitors that bind to the active site

Question 27

What is noncompetitive inhibition?

Answer 27

Inhibitors that bind to a different part of the enzyme than the active site

Question 28

How does a competitive inhibitor change the Vmax?

Answer 28

No change

Question 29

How does a competitive inhibitor change the Km?

Answer 29

Increase

Question 30

How does a noncompetitive inhibitor change the Vmax?

Answer 30

Decrease

Question 31

How does a noncompetitive inhibitor change the Km?

Answer 31

No change

Question 32

What kind of bond does irreversible inhibitors form with the active site?

Answer 32

Covalent bond

Question 33

How can you displace the reversible inhibitors?

Answer 33

By increasing the amount of substrates

Question 34

2 most common types of inhibitors

Answer 34

Competitive
Uncompetitive

Question 35

Example of competitive inhibitor drug

Answer 35

Sulfanilamide

Question 36

What does methotrexate inhibit?

Answer 36

DNA synthesis

Question 37

Where does the lineweaver-burk plot of a competitive inhibitor intersect with that one no inhibitor?

Answer 37

At the y axis

Question 38

What does a non competitive inhibitor effect, the enzyme activity or the ability to bind?

Answer 38

The enzyme activity

Question 39

Where does the lineweaver-burk plot of a noncompetitive inhibitor intersect with that one no inhibitor?

Answer 39

At the x-axis

Question 40

What can irreversible inhibitors be used to map?

Answer 40

The active site

Question 41

How does suicide inhibitors work?

Answer 41

They bind to the enzyme as a substrate and when catalysis occur they are modified into an irreversible inhibitor

Question 42

What does penicillin do?

Answer 42

Irreversibly inactivate a key enzyme in bacterial cell-wall synthesis

Question 43

What is the reactive site of penicillin?

Answer 43

The peptide bond of its beta-lactam ring

Question 44

Does uncompetitive inhibitors have affinity for free enzymes?

Answer 44

Very little

Question 45

What does uncompetitive inhibitors mainly bind to

Answer 45

Enzyme-substrate complex

Question 46

What is mixed inhibition?

Answer 46

When the inhibitor can bind both to the free enzyme and the enzyme-substrate complex

Question 47

How does a mixed competitive inhibitor change the Vmax?

Answer 47

Decreases

Question 48

How does a mixed competitive inhibitor change the Km?

Answer 48

No change

Question 49

What does penicillin bind to?

Answer 49

Transpeptidase

Question 50

What kind of inhibitor is penicillin?

Answer 50

Suicide inhibitor