Dose-Response Curves

Question 1

What is EC50?

Answer 1

Concentration of drug that gives half the maximal response.

Question 2

What shape is the graph when it is a linear plot?

Answer 2

Curve of decreasing gradient up to Qmax.

Question 3

What shape is the graph when it is a semi-log plot?

Answer 3

Sigmoid curve. Q max against log(agonist). logEC50 is the vertical part.

Question 4

What is the dissociation constant (Kd)?

Answer 4

The concentration at which half the drug is bound to the receptor at equilibrium.

Question 5

What is the Law of Mass Action?

Answer 5

The rate of a chemical reaction is proportional to the product of the concentrations of the reactants.

Question 6

At equilibrium, what is the relationship between the association rate constant, dissociation rate constant, equilibrium dissociation constant?

Answer 6

[ligand].[receptor]/[ligand receptor complex] = k(off)/k(on) = k(d)
drugs with higher affinity have lower k(d)