Drug-receptor interactions

Question 1

Definition of a drug?

Answer 1

a chemical substance that interacts with a biological system to produce a physiological effect

Question 2

What are the 4 main drug target sites?

Answer 2

• receptors
• ion channels
• transport systems
• enzymes

Question 3

What are receptors? what activates them?

Answer 3

• proteins within cell membranes
• activated by neurotransmitters or hormones
• there are 4 types of receptors with different structures and transduction systems

Question 4

What are examples of drugs that act on receptors?

Answer 4

• acetylcholine

- atropine -muscarinic cholinoceptor antagonist used to dry up secretions

Question 5

Definition of antagonist?

Answer 5

substance that interacts and binds to a receptor but does not produce a response - it acts as a blocker

Question 6

Definition of agonist?

Answer 6

a substance that acts at a cell receptor site to produce an effect that is the same as , or similar to, the body’s normal chemical messenger

Question 7

What are ion channels? and how may types are there?

Answer 7

• selective pores in the lipid bilayer that allow the passage of ions in/out of the cell dependant on the electrochemical gradient
• voltage sensitive
• receptor linked e.g. nicotinic acetylcholine receptor

Question 8

What examples of drugs work on ion channels?

Answer 8

• Local anaesthetic block voltage gated sodium channels of sensory axons
• calcium channel blockers- block voltage gated calcium channels

Question 9

What are transport systems? Give examples.

Answer 9

-transport substances against their concentration gradient e.g. glucose, ions, neurotransmitters

Examples: Na/K pump and noradrenaline uptake 1

Question 10

What examples of drugs work on transport systems?

Answer 10

• tricyclic antidepressants
• cardiac glucosides - slow down the action of the Na/K pump, increasing the conc of intracellular Ca, increasing the force of contraction

Question 11

What are the three was in which drugs interact with enzymes? Provide examples for each one

Answer 11

• enzyme inhibitors (neostigmine works on anticholinesterases)
• False substrates (methyldopa is an antihypertensive)
• Prodrugs ( chloral hydrate needs to be converted to trichloroethanol in the liver)

Question 12

What are the unwanted effects of drugs that act on enzymes?

Answer 12

In the case of paracetamol, if you take an overdose all the liver’s microsomal enzymes become saturated and another set of enzymes (P450) start breaking it down instead

• the metabolites of this can have effect on your liver and kidney
• this is irreversible

Question 13

Which 3 drugs are non-specific?

Answer 13

• general anaesthetics
• antacids
• osmotic purgatives

Question 14

Definition of potency

Answer 14

how powerful the drug is, depends on affinity and efficacy

Question 15

Definition of affinity

Answer 15

how willing the drug is to bind to its receptor

Question 16

Definition of efficacy

Answer 16

the ability of a drug to stimulate a response once bound to the receptor

Question 17

Define full agonist

Answer 17

an agonist that generates the maximal response

Question 18

Define partial agonist

Answer 18

an agonist that generates less than the maximal response

Question 19

Define selectivity

Answer 19

preference for interacting with a particular receptor type

Question 20

Structure-activity relationship?

Answer 20

emphasizes the relationship between the structure of a drug and its activity
-companies exploit this, they can take an agonist and make a small structural change to make an antagonist

Question 21

What does a log dose response curve look like?

Answer 21

the full agonist is furthest to the left at maximum height
the full agonist with lower affinity is in the middle at maximum height
the partial agonist peaks a lot sooner than the others and is furthest to the right

Question 22

What are the two types of antagonist?

Answer 22

• competitive

- irreversible

Question 23

Describe the mechanism of competitive antagonists

Answer 23

• bind to the same site as the agonist
• increasing the conc. of the agonist can overcome the antagonist actions
• responses are surmountable

Question 24

What effect does a competitive antagonist have on the dose-response curve?

Answer 24

• shifts to the right

Question 25

Examples of competitive antagonists

Answer 25

• atropine (muscarinic cholinoceptor)

- propranolol (beta blocker)

Question 26

Describe the mechanism of irreversible antagonists

Answer 26

• if they bind to the same site they do so with covalent bonds and more tightly
• some bind to a different site and cause insurmountable antagonism

Question 27

Example of irreversible antagonist

Answer 27

-hexamethonium

Question 28

What effect does irreversible antagonist have on the dose response curve?

Answer 28

• shifts to the right and falls away as the maximum response won’t be generated