DRUG TARGETS 1

Question 1

Explain affinity?

Answer 1

Affinity is the attraction of a ligand(drug) for its receptor (shapes, charges)

Question 2

Explain efficacy?

Answer 2

Tendency of the drug once bound, to activate the receptor is called efficacy. Maximum effect=1 Minimum effect=0

Question 3

Explain specificity?

Answer 3

Specificity means that the drug can only bind to one receptor type.Weak affinities for everything else which can cause unwanted side effects.

Question 4

Explain selectivity?

Answer 4

Preferential binding to a certain subtype(of a receptor family) leads to a greater effect at that subtype than others.

• eg salbutamol at B2(lungs) rather than B1(heart)
• Selectivity for H1 receptors is how current antihistamines work.
• Chemotherapy is designed to be selective for cells/organisms it is targeting.

Question 5

Explain the receptor occupancy theory?

Answer 5

Drug effect is proportional to the number of receptors occupied.

Question 6

Explain the rate theory?

Answer 6

Drug effect is proportional to the rate of occupancy

Question 7

Explain the floating receptor model?

Answer 7

the D-R complex may interact with a variety of effectors in the membrane to produce its effect.

Question 8

Explain the two state model?

Answer 8

the receptors exist in active or inactive form

Question 9

What is the symbol for Inactive form?

Answer 9

R

Question 10

What is the symbol for the active state?

Answer 10

R*

Question 11

Describe what happens to the equilibrium in the 2-state model when no ligand is bound?

Answer 11

Equilibrium favours R(inactive state)

Question 12

What is an agonist?

Answer 12

A drug which binds and activates the receptor.

Question 13

Describe what happens to the 2-state model with the full agonist?

Answer 13

Full agonist- efficacy of 1

Equilibrium strongly shifted to R*(active state)

Question 14

Describe what happens to the 2-state model with the partial agonist?

Answer 14

Efficacy between 0 and 1.

Equilibrium partially shifted to R(active state) ie there is a weak preference for R

Question 15

Describe what happens to the 2-state model with an inverse agonist?

Answer 15

The inverse agonist has a higher affinity for R than R* and so shifts the equilibrium to the left.

Question 16

What is an antagonist?

Answer 16

A drug which binds to the receptor without causing activation but prevents the agonist from binding.

Question 17

Describe what happens to the 2-state model with an antagonist?

Answer 17

Efficacy of 0
No preference for either state
Equilibrium not shifted.

Question 18

What is the term receptor plasticity referred to?

Answer 18

Receptor states and populations are never constant. Thus plasticity refers to the changes in effectiveness of the drug over time in response to these changes in receptor populations.