Drug-Receptor Interactions 2

Question 1

Affinity

Answer 1

A measure of the concentration range over which a drug binds to its receptor.

Kd

Question 2

Efficacy

Answer 2

The ability of a drug to generate/initiate a stimulus once bound to its receptor

Question 3

Function of partial agonists

Answer 3

Reduce the response to a full agonist because some receptors will be occupied by partial agonist molecules.

This gives a smaller response than if all the receptors were occupied by full agonist molecules.

Question 4

What is a competitive antagonist ?

Answer 4

A drug which interacts/binds REVERSIBLY with receptors to form a complex, but this complex doesn’t evoke a response.

Question 5

[D]

Answer 5

Concentration of drug

Question 6

State the competitive antagonist equation

Answer 6

[D] + [R] + [A] = [DR] + [AR]

Question 7

[R]

Answer 7

Concentration of receptor

Question 8

[A]

Answer 8

Competitive antagonist

Question 9

[DR]

Answer 9

Only [DR] gives rise to a response

Question 10

[AR]

Answer 10

Receptors which are occupied by not activated

Question 11

Ka

Answer 11

The equilibrium dissociation constant for an antagonist

Question 12

Describe log dose-response curves for a competitive antagonist

Answer 12

Displaced to the right

Maximum response to agonist remain the same (linear sections are parallel)

Question 13

What does the log dose response curve moving to the right in response to an antagonist mean ?

Answer 13

More of the receptor sites are being occupied

Question 14

r

Answer 14

Ratio by which [D] must be increased to overcome competition by [A]

Question 15

Describe Ka

Answer 15

The concentration of antagonist that makes it necessary to add twice as much agonist to produce a response as would be needed in the absence of the antagonist

Question 16

pA2

Answer 16

-log10(Ka)

Compares the affinity of an antagonist

Question 17

Describe the log dose-response curve of irreversible competitive antagonism

Answer 17

Slope is decreased

Maximum response to agonist is decreased

Question 18

Allosteric Modulators

Answer 18

Bind to sites on the receptor other than the agonist binding site and can modify agonist activity.

Question 19

Describe allosteric binding sites

Answer 19

Allosteric binding sites are regulatory, not active binding sites.

Question 20

Function of allosteric binding sites

Answer 20

Can modify the affinity or efficacy of a receptor’s endogenous ligand or drug.

Potentiate or inhibit

Question 21

Non-competitive antagonist

Answer 21

These are an example of allosteric modulation

The antagonist blocks access of the agonist to its binding site through steric hinderance.

Question 22

How quickly does an irreversible competitive antagonist dissociate from the receptor ?

Answer 22

Very slowly (if at all)

Question 23

What effect does a non-competitive antagonist have on efficacy ?

Answer 23

Efficacy is lowered

Question 24

What effect does a non-competitive antagonist have on affinity ?

Answer 24

Receptor can alter conformation and binding affinity of agonist so affinity is lowered.

Question 25

What is an inverse agonist ?

Answer 25

An agonist that decreases the activity of the receptor from basal level

Question 26

Homeopathy

Answer 26

The dilution and potency of medicines is inversely proportional.

Higher dilution, the more potent the medicine

Question 27

If drug A has a Kd value of 8nM, and drug B has a Kd value of 100nM

Which drug has the greatest affinity for the receptor ?

Answer 27

Drug A

Question 28

Drug A has a pD2 value of 2 and drug B has a pD2 value of 6

Which has the greatest affinity for the receptor ?

Answer 28

Drug B

(higher pD2 value means lower Kd)

Question 29

Both drug A and drug B have a pD2 value of 2.

At the same concentration, drug A produces 50% of the effect seen with drug B.

Which has the greatest affinity ?

Answer 29

Neither

Question 30

Concerning drug receptor interactions, the Kd refers to ?

Answer 30

The drug concentration required to occupy 50% of receptors at equilibrium.

Question 31

State the true statement :

Competitive inhibition is based on reversible drug/antagonist binding at receptor sites.

With competitive inhibition, the dose-effects curve is shifted to the left

With competitive inhibition, maximal drug effect cannot be obtained, even at high agonist concentrations.

All of the above

Answer 31

Competitive inhibition is based on reversible drug/antagonist binding at receptor sites.

Question 32

Non-competitive antagonists can be surmounted with high concentrations of agonist

True or False

Answer 32

False

AKA Allosteric Modulators