Basic words and meanings

Question 1

What does pharmacodynamics mean?

Answer 1

The effects of the drug on the body

Question 2

What does pharmacokinetics mean?

Answer 2

The way the body affects the drug over time

• absorption
• distribution
• metabolism
• excretion

Question 3

What is a receptor, name the 4 key types?

Answer 3

A protein molecule that is activated by transmitters or hormones

1. Ligand-gated channels
   - e.g. nicotinic receptor, GABA receptor
2. G-protein coupled receptors
   - linked to physiological responses by 2nd messengers
3. Nuclear receptors for steroid hormones
4. Kinase-linked receptors
   - intrinsic tyrosine kinase activity
   - e.g. insulin, cytoline receptors

Question 4

How do second messengers work?

Answer 4

The receptor is activated by its agonist and the second messenger concentration increases (or decreases) triggering processes that result in a cellular response
- e.g. cAMP, Ca2+, InsP3 and DG

Question 5

Discuss the steps involved in G-protein signalling.

Answer 5

1. Ligand binds to G-protein coupled receptor causing a conformation change to activate the G-protein inside the cell
2. GDP is converted to GTP
3. the alpha subunit dissassociates with the GTP attached and activates (or inhibits) the effector protein
4. The signalling (second messenger) cascade is then activated (or inhibited)
5. GTP is hydrolysed back to GDP

Our friend Armando has a video on this on youtube

Question 6

What is a G-protein?

Answer 6

Made up of a alpha, gamma, beta subunits

- activate second messengers within the cell

Question 7

What does drug affinity mean?

Answer 7

How avidly a drug binds to its receptor

Question 8

What is an antagonist, name the 2 main types.

Answer 8

A drug that binds to receptors but do not activate them

1. Competitive antagonists
   - bind reversibly
   - higher doses of agonist can overcome the affects of the antagonist pushing the dose response curve to the right
2. Irreversible antagonists
   - cannot be reversed by increasing the amount of agonist

Question 9

What is a partial agonist?

Answer 9

An agonist that does not elicit the same response as a full agonist
- possible that this is due to a lower affinity of the agonist for the receptor

Question 10

What is tachyphylaxis?

Answer 10

When a drug is given repeatedly, its effects decrease with time.

• If this occurs quickly (minutes) this is called tachyphylaxis.
• If this occurs over days-weeks it is called tolerance.

Tachyphylaxis is caused by

• depletion or marked reduction of the amount of neurotransmitter responsible for creating the drug’s effect
• depletion of receptors available to which the drug or neurotransmitter can bind