Receptor theory

Question 1

Define a receptor

Answer 1

Proteins in the cell membrane which bind ligands with high affinity and transduce a signal to produce a biological effect

Question 2

Define a ligand

Answer 2

A ligand is a substance that forms a complex with a receptor (or other biomolecule) to serve a biological purpose

Question 3

A ligand only binds a receptor if it has -

Answer 3

Affinity

Question 4

The rate that ligands come into contact with
receptors is controlled by -

Answer 4

diffusion

Question 5

What interactions form between ligand and the receptor

Answer 5

• Polar and hydrophobic interactions and h bonds can form
• Interactions between the ligand and amino acid residue within the receptor contribute to affinity

Question 6

The greater the affinity a ligand has for its
receptor, the –

Answer 6

The greater the affinity a ligand has for its
receptor, the longer it remains bound
before dissociating

Question 7

The number of ligand-receptor complexes is controlled by:

Answer 7

• The rate of association and dissociation at
  equilibrium
• The concentration of ligand
• The number of receptors

Question 8

How to measure the amount of drug ligand binding

Answer 8

Question 9

Binding assay graph: what does total and non-specific binding show

Answer 9

Total - non specific = specific

Question 10

What do binding studies tell
us?

Answer 10

• They also allow us to compare drug actions, screening drugs against different receptors

Question 11

Which of these has the highest affinity

Answer 11

• They one with the lowest
• Binds even at low concentration
• Drug c

Question 12

Which of these drugs is most selective for receptor 1?

Answer 12

• Drug B
• More selectivity for receptor 1 then 2
• Greatest difference

Question 13

Answer 13

Question 14

What is EC50 and Emax

Answer 14

• EC50 is the concentration that gives 50% of the response = potency
• From functional assay curves

Question 15

Answer 15

Question 16

What is bmax and Kd

Answer 16

binding assay curves

Question 17

summary

Answer 17

Question 18

What are binding and functional assays used for

Answer 18

*Binding assays are used by pharmaceutical
industry to design and characterise properties of
new drugs
*Obtain binding kinetics, affinity and selectivity
*Functional assays are used to generate
concentration response curves
*help work out potency, efficacy and selectivity
*These properties are vital to understand why
different agonist drugs have different therapeutic
and off target effects even if they target (are ligands
for) the same receptors

Question 19

What is an antagonist

Answer 19

• A drug that binds to a receptor but does not activate a response
  *zero efficacy (Emax = 0)
• A drug that blocks the action of an agonist when bound

Question 20

Testing for antagonism

Answer 20

Question 21

Different types of antagonist

Answer 21

Question 22

Competitive antagonism

Answer 22

• Can be overcome by increasing conc of agonist

Question 23

Irreversible antagonists

Answer 23

Question 24

What information can we read off a specific binding plot

Answer 24

• B max
• Kd

Question 25

How can we estimate the potency of the antagonist

Answer 25

By finding the IC50
(the concentration of
antagonist required to reduce
the agonist response by 50%)

Question 26

What effect do competitive antagonists have

Answer 26

Question 27

How does competitive vs non competitive biological assays look different

Answer 27

Question 28

What is a partial agonist and how does it effect Emax

Answer 28

• Some agonists cannot evoke the maximal response