Question 1

Which of the following best describes the difference between affinity and efficacy in drug-receptor interactions?

Accepted Answer

Affinity is the tendency of a drug to bind a receptor, while efficacy is the ability of the drug to activate the receptor after binding.

Question 2

A drug has a dissociation constant $$K_D of$$ $$1 	imes 10$$^{-8}$$ M. What does this value indicate about the drug's affinity for its receptor?

Accepted Answer

The drug has a high affinity for its receptor because a low $$K_D$$ means less ligand is needed for 50% receptor occupancy.

Question 3

Which equation correctly represents the proportion of occupied receptors ($$P) $$given agonist concentration $$[A]$$ and dissociation constant $$K_D$$?

Accepted Answer

$$P = \frac{[A]}{K_D + [A]}$$

Question 4

In a bioassay using an organ bath, increasing the concentration of acetylcholine eventually leads to a plateau in muscle contraction. What is the most likely explanation for this observation?

Accepted Answer

All available receptors are saturated, so further increases in acetylcholine concentration cannot elicit a greater response.

Question 5

Which of the following statements about competitive antagonists is TRUE?

Accepted Answer

A competitive antagonist reduces the potency of an agonist but does not affect the maximum efficacy.

Question 6

The equilibrium association constant ($$K_A) is $$related to the dissociation constant ($$K_D) by $$which of the following relationships?

Accepted Answer

$$K_A = \frac{1}{K_D}$$

Question 7

A patient with asthma is prescribed salmeterol instead of salbutamol. Based on pharmacodynamics, why is salmeterol preferred for severe asthma?

Accepted Answer

Salmeterol has a higher affinity for the receptor and remains bound longer, providing extended relief.

Question 8

Which of the following best describes the effect of a non-competitive (irreversible) antagonist on an agonist's concentration-response curve?

Accepted Answer

The maximum efficacy ($$E_{max}) is $$reduced, and increasing agonist concentration cannot restore it.

Question 9

If the $$EC_{50} of a $$drug is $$2 	imes 10$$^{-7}$$ M, what does this value represent?

Accepted Answer

The concentration of the drug required to produce 50% of its maximum effect.

Question 10

Which of the following is TRUE regarding the $$pA_2$$ value for a competitive antagonist?

Accepted Answer

$$pA_2 is $$the negative logarithm of the molar concentration of antagonist required to produce a two-fold shift in the agonist concentration-response curve.

Question 11

A partial agonist is characterized by which of the following properties?

Accepted Answer

It produces a lower maximal response ($$E_{max}) $$than a full agonist, even at high concentrations.

Question 12

Which of the following best explains why increasing the concentration of a competitive antagonist requires a higher concentration of agonist to achieve the same effect?

Accepted Answer

The antagonist competes for the same binding site, so more agonist is needed to outcompete the antagonist for receptor occupancy.

Question 13

Which of the following is the correct definition of the inhibition constant ($$K_i) in a $$competition assay?

Accepted Answer

$$K_i is $$the concentration of competing ligand required to occupy 50% of the receptors in the absence of radioligand.

Question 14

Which of the following statements about the law of mass action in drug-receptor binding is correct?

Accepted Answer

The magnitude of response depends on drug concentration, proportion of occupied receptors, and the rate of formation/dissociation of drug-receptor complexes.

Question 15

Which of the following is the correct value for Avogadro's constant?

Accepted Answer

$$6.022 	imes 10$$^{23}$$ mol$$^{-1}$$

Question 16

A drug is found to have a high $$K_A$$ and a low $$K_D. $$What does this indicate about the drug's interaction with its receptor?

Accepted Answer

The drug binds strongly to the receptor, indicating high affinity.

Question 17

Which of the following best describes the effect of an irreversible antagonist on the response to an agonist?

Accepted Answer

The maximum response ($$E_{max}) is $$decreased, and increasing agonist concentration cannot restore it.

Question 18

Which of the following is a real-world example of an agonist and its effect?

Accepted Answer

Salbutamol binds to bronchial receptors and causes airway dilation in asthma patients.

Question 19

Which of the following statements about partial agonists is correct?

Accepted Answer

Partial agonists produce less than the maximal response even when all receptors are occupied.

Drug-Receptor Interactions: Agonists, Antagonists, and Pharmacological Principles

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