DRUG RECEPTOR INTERACTIONS

Question 1

What is the fastest type of receptor response?

Answer 1

Opening or closing of Ion channels upon binding with a ligand

Question 2

Define ‘mean channel lifetime’

Answer 2

The duration of the a response following activation of a ion channel by receptor binding

Question 3

How do secondary messengers alter intracellular functions?

Answer 3

They generate protein kinase activation and phosphorylation of membrane proteins

Question 4

Give an example of a second messenger.

Answer 4

Adenyl cyclase

Question 5

What cyclicAMP?

Answer 5

A nucleotide synthesised from ATP by adenyl cyclase

Question 6

how is cyclicAMP inactivated?

Answer 6

It is converted into 5’AMP by phosphodiesterases

Question 7

What components are required to generate a secondary messenger?

Answer 7

1. Receptor protein: that faces outside of the cell
2. G protein: transmembrane protein that faces inwards (toward the cytoplasm)
3. Adenyl cyclase
4. cAMP dependent protein kinase

Question 8

What is the effect of cholera toxin?

Answer 8

It inhibits the secondary messenger system. It binds to G protein in intestinal mucosa and prevents hydrolysis of GDP to GTP and therefore inhibits activation of adenyl cyclase which is used to produce other secondary messengers such as cAMP

Question 9

What is the function of G proteins?

Answer 9

Hydrolysis GTP to GDP, in doing so it opens calcium ion channels resulting in calcium influx and activates adenyl cyclase.

Question 10

What form is most calcium in the body present in?

Answer 10

It is in skeleton in the form of hydroxyapatitem

Question 11

How much calcium is in the blood?

Answer 11

2.5mmol/l

Question 12

What percentage of calcium in the blood is free and what percentage is bound to protein?

Answer 12

50% is free in the blood and 50% is bound to proteins or complexed with anions.

Question 13

What percent of calcium is found intracellularly?

Answer 13

1%

Question 14

What is the intracellular calcium concentratio?

Answer 14

10-7m

Question 15

Which hormones and regulators act via calcium channels?

Answer 15

• muscarininc agonists
• a1 agonists
• histamine
• serotonin

Question 16

What intracellular effects take place when intracellular calcium is increased?

Answer 16

-Minor membrane phospholipids (phosphatidyl inositol) break down which increases the permeability of the membrane to calcium
-‘Flip Flop’ mechanisms: phosphatidylethanolamine is converted into phasphatidylcholine, this further increases membrane permeability to calcium
-

Question 17

What intracellular protein controls the intracellular effects of calcium?

Answer 17

Calmodulin- activates many different intracellular enzymes

Question 18

How is calcium-calmodulin complex inactivated?

Answer 18

Trifluoperazine (antipsychotic)

Question 19

Where do steroid hormones bind?

Answer 19

DNA binding sites

Question 20

How are steroids hormones able to bind to DNA?

Answer 20

They are lipophilic which means they can easily diffuse through the cell membrane as well as the nuclear membrane and bind directly to DNA. They increase the production of RNA polymerase and therefore increase transcription

Question 21

What is ‘half maximal binding’?

Answer 21

It is a measure of the affinity of a ligand to its receptor. It measures how much ligand is required to bind to 50% of its available receptors.

Question 22

What is a partial agonist?

Answer 22

A ligand that has both agonist and antagonist effects, therefore the maximal response is lower than a pure agonist.