enzyme II: competitive and non-competitive inhibition

Question 1

what is enzyme inhibitors?

Answer 1

Many enzymes can be inhibited by the binding of small ions and molecules

Many drugs work this way

Question 2

list all enzyme inhibitors

Answer 2

1 Reversible inhibition: 2 types
Competitive
Non-competitive
2 Irreversible inhibition
3 Uncompetitive inhibition
4 end product inhibition
5 zymogens

Question 3

what is competitive inhibition ?

Answer 3

when an inhibitor has a similar structure to substrate. this allows inhibitor to bind to the active site and occupy active site. this decreases rate of reaction. However , the addition of more substrate will solve this problem.

Question 4

name a competitive inhibitor and describe its function and consequence.

Answer 4

disulfiram (Antabuse) inhibits the aldehyde oxidase

which causes the accumulation of acetaldehyde with subsequent unpleasant side effects of nausea and vomiting.

Question 5

what is Methanol poisoning

Answer 5

Methanol is oxidized to formaldehyde and formic acid which attack the optic nerve causing blindness.

Question 6

what it the antidote for methanol poisoning?

Answer 6

Ethanol is given as an antidote

Question 7

how does this antidote for methanol poisoning work?

Answer 7

Ethanol competitively inhibits the oxidation of methanol.
Ethanol is oxidized in preference to methanol
Consequently, the oxidation of methanol is slowed down and the toxic by-products do not have a chance to accumulate.

Question 8

what is non-competitive(allosteric ) inhibition?

Answer 8

an inhibitor bind to enzyme other than its active site. this distorts the active site. this causes the substrate to not bind to the active site as it is not complementary to active site .

Question 9

what is allosteric activation?

Answer 9

this is when a substance binds to enzyme other than the active site. this causes the active site to distort and become complementary to substrate.

Question 10

name a non-competitive inhibitor

Answer 10

Nifedipine

Question 11

what is the function of Nifedipine

Answer 11

is a calcium channel blocker, it inhibits Ca2+ dependent ATPase
Prevents the uptake of calcium into cardiac cells

Question 12

what’re the uses of Nifedipine?

Answer 12

Its main uses are is to treat angina and high blood pressure

Question 13

what’s the effect of competitive, non-competitive inhibito rs on the rate of reaction?

Answer 13

the rate of reaction decreases and lower Vmax for the non-competitive inhibitor. same V-max for competitive and normal but takes more conc of S to reach the Vmax.

Question 14

describe the lineweaver-burk plots for inhibition(competitive, non-competitive, un competative )

line crossing at y axis
parallel line
two lines start at the same point and move away.

Answer 14

competitive:
Km increased
Vmax unaffected
uncompetitive:
Km reduced 
Vmax reduced
noncompetitive:
Km unaffected
Vmax reduced

Question 15

what are irreversible inhibitors?

Answer 15

Bind so tightly to the enzyme (often by a covalent bond) they cannot be removed

Question 16

give an two example of an irreversible inhibitor and its mode of action

Answer 16

Sarin binds to a Serine residue in acetylcholinesterase, preventing nerve impulse transmission.

Aspirin covalently modifies prostaglandin H2 synthase, reducing synthesis of inflammatory signals

Question 17

what is Uncompetitive inhibition?

Answer 17

The inhibitor binds to enzyme substrate complex causing a shift in the equilibrium. This causes a greater affinity for the reaction to produce more ES complexes

Question 18

give an example of a Uncompetitive inhibitor

Answer 18

Lithium is used to treat manic-depressive psychosis.

Suggested that it inhibits inositol monophosphatase.

Question 19

what is End-product inhibition?

Answer 19

in a series of enzyme-controlled reaction the end product acts as the inhibitor. it does this by binding to the allosteric site of enzyme 1 of the multistep process. this is so that the enzyme stops producing more product than nedded.
Important control for complex multi-step processes

Question 20

what are zymogens ?

Answer 20

Some enzymes are initially produced as an inactive precursor form known as zymogen. The zymogen form is typically a longer polypeptide that must be hydrolyzed at a specific location to produce the active form of the enzyme
Cleavage at the activation site(s) may release a polypeptide known as the “pro-sequence”, and results in activation of the enzyme

Question 21

where else is enzymes regulated?

Answer 21

Gene expression

Phosphorylation

Proteolysis