Enzyme Inhibition (Quiz 1)

Question 1

____________ are chemicals that reduce the rate of enzymic reactions.

• are usually specific and they work at low concentrations.
• block the enzyme, but they do not usually destroy it.
• Many drugs and poisons are ______ of enzymes in the nervous system.

Note: Same Answer

Answer 1

Inhibitors

Question 2

Type of Enzyme Inhibitors (2)

Answer 2

• Nonspecific
• Specific

Question 3

Type of Enzyme: Nonspecific Inhibitor (7)

Answer 3

Denaturation,
pH,
temperature,
Acids & bases,
Alcohol,
Heavy Metals,
Reducing Agents

Question 4

Type of Specific Inhibitors (2)

inhibition can be ________ or __________

Answer 4

• Irreversible Enzyme Inhibitors
• Reversible Enzyme Inhibitors

Question 5

Certain compounds inhibit enzymes - decrease the rates of their ___________

Answer 5

catalysis

Question 6

3 types of reversible Inhibitors

The various types of inhibitors can be distinguished by the kinetics of their inhibition.

Answer 6

o competitive inhibitors
o non-competitive inhibitors
o un-competitive inhibitors

Question 7

suicide inhibitors

Answer 7

Irreversible inhibition

Question 8

If covalently bond to enzyme, bond relatively easily be ________. i.e. hydrol. of ester

Answer 8

broken

Question 9

____ Enzyme Inhibition:

is a compound that binds to an enzyme and interferes with its activity. Many drugs are enzyme ___________

Answer 9

Reversible Enzyme Inhibition
inhibitor

Question 10

The effect of enzyme inhibition:

Combine with the functional groups of the amino acids in the active site, irreversibly.

Examples: nerve gases and pesticides, containing organophosphorus, combine with serine residues in the enzyme acetylcholine esterase.

Answer 10

Irreversible inhibitors

Question 11

These can be washed out of the solution of enzyme by dialysis.

Answer 11

Reversible inhibitors

Question 12

The substrate [S] and the inhibitor [I] compete for the same site on the enzyme.

Answer 12

Classical Competitive Inhibition

Question 13

• [I] binds to [E] only
  In the presence of this inhibition
• Km increases,
• Vm remains unchanged or stays the same

Answer 13

Competitive Inhibition

Question 14

• its inhibitor mimics substrate
• fits into active site

Answer 14

Competitive Inhibition

Question 15

__________ is a competitive inhibitor of succinate dehydrogenase

• has a structure that is similar to succinate.
• inhibition is reversed by adding succinate

Answer 15

Malonate

Question 16

The effects of competitive inhibition can be overcome by increasing _________

Answer 16

Substrate [S]

Question 17

_________ Inhibitor mimic substrate may block active site but may dislodge it.

Answer 17

Competitive Inhibitor

Question 18

Competition depends upon_________

Answer 18

concentration

Question 19

Many competitive inhibitors are substrate ___________

Answer 19

analogs (def. chemical compound that resembles substrate)

Question 20

Benzamidine is an inhibitor of the enzyme ____________

Answer 20

trypsin

Question 21

Many competitive inhibitors are substrate analogs. Ex.:

An inhibitor of the enzyme Purine Nucleoside Phosphorylase, that utilizes ____________ and is possible drug for the treatment of arthritis

Answer 21

Guanosine

Question 22

• inhibitor binds to a site other than the active site.
• The effects of this inhibition cannot be overcome by increasing substrate [S]

Answer 22

Non-competitive Inhibition

Question 23

In the presence of this inhibitor
o Km stays the same
o Vmax decreases

Answer 23

non-competitive inhibitor

Question 24

A noncompetitive inhibitor has a structure that is different than that of the substrate

o it binds to an ___________ site rather than to the active site

o it distorts the shape of the enzyme, which alters the shape of the active site and prevents the binding of the __________

Answer 24

• allosteric site
• substrate

Question 25

These are **not influenced by the concentration of the substrate**. It **inhibits by binding irreversibly** to the enzyme but **not at the active site**.

Answer 25

Non-competitive

Question 26

The effect of enzyme inhibition: Examples * **Cyanide combines with the Iron** in the enzymes _________. * Heavy metals, Ag or Hg, combine with -SH groups. These can be **removed** by using a **chelating agent** such as____________.

Answer 26

cytochrome oxidase EDTA

Question 27

Inhibitor **binds to a site other than the active site**, but **only when substrate is bound**

Answer 27

Un-competitive inhibition

Question 28

In the presence of an this inhibitor: o **Km decreases** o **Vmax decreases** The **effects** of this inhibition **cannot be overcome by Increasing [S]**

Answer 28

Un-competitive inhibition

Question 29

_____________ enzyme inhibition - Some inhibitors are compounds that **form a stable covalent bond with the target enzyme**. Ex. **Diisopropyl fluorophosphate (DFP) inactivates** _________ proteases by **covalently modifying** an active site on its residue.

Answer 29

- **Irreversible** Enzyme Inhibition - **serine** proteases

Question 30

An _________ inhibitor **destroys enzyme activity**, usually by **bonding with side-chain groups** in the active site

Answer 30

Irreversible inhibitor

Question 31

The **activity of some enzymes is regulated by reversible** _______ ex. pyruvate dehydrogenase

Answer 31

Phosphorylation

Question 32

- used to **control a sequence of reactions** - **reaction product** may **block initial enzyme**.

Answer 32

Regulator or feedback