Week 8 - Drugs and Receptors

Question 1

Define the term “ligand”.

Answer 1

Molecule (or e.g. ion) that binds specifically to a receptor

Question 2

Define the terms “agonist” and “antagonist”.

Answer 2

Agonist: Cause activation of a receptor
Antagonist: Blocks the binding of an agonist and therefore, prevents receptor activation

Question 3

What is the binding of a ligand to a receptor governed by?

Answer 3

Affinity

Higher affinity = stronger binding

Question 4

Define the term “affinity”.

Answer 4

This refers to the strength of interaction between the drug and the receptor.

Question 5

What is receptor activation governed by?

Answer 5

Intrinsic efficacy: How well the agonist switches the receptor into its active conformation

Question 6

Distinguish between intrinsic efficacy and efficacy.

Answer 6

Intrinsic efficacy refers to how good the ligand is at generating the active conformation of the receptor.
Efficacy is governed both by intrinsic efficacy, and other cell/tissue-dependent factors that determine response, and therefore is the ability of a ligand to cause a response.

Question 7

How do we measure drug-receptor interactions by binding?

Answer 7

Often by binding of a radioactively labelled ligand (radioligand) to cells or membranes prepared from cells

Question 8

What is Bmax? What does it give us information about?

Answer 8

Bmax refers to the maximum binding capacity. This gives us information about the number of receptors.

Question 9

What is Kd? What is it a measure of?

Answer 9

Kd is the dissociation constant, and is a measure of affinity. It is the concentration of ligand required to occupy 50% of the available receptors. A lower value of Kd suggests higher affinity (Kd is the reciprocal of affinity), because a lower concentration of drug is required to occupy 50% of receptors.

Question 10

Define EC50. What does it indicate about a drug and which factors does it depend on?

Answer 10

Effective concentration giving 50% of the maximal response
It is a measure of agonist potency - it depends on both affinity and intrinsic efficacy plus cell/tissue-specific components that allow something to happen.

Question 11

Distinguish between concentration and dose.

Answer 11

Concentration: Known concentration of drug at site of action, e.g. in cells and tissues
Dose: Concentration at site of action is unknown

Question 12

Write an equation for molarity.

Answer 12

Molarity = g/L divided by molecular weight

Molecular weight x Molarity = g/L