Lecture 03 - Receptors and Membrane Signalling

Question 1

How can cell function be altered?

Answer 1

1. Alternating membrane potential - causes a change in activity
2. Altering enzyme activity - e.g. glucose metabolism
3. Altering gene expression - control proteins, hence control the nature of the cell

Question 2

How can cell function be affected?

Answer 2

Cell function may be affected directly or via receptors.

Question 3

What are four types of drug receptors?

Answer 3

1. Enzymes e.g. cyclooxygenase receptor for aspirin
2. Ion channels e.g. Ca channels
3. Transporters e.g. noradrenaline
4. Physiological e.g. receptors for hormones and NTs such as Ach. (Have both agonists and antagonists unlike the other types)

Question 4

How are receptors classified?

Answer 4

1. On the basis of the selective action of drugs.
2. Named according to the transmitter or hormone with which they interact. E.g. Ach receptor
3. Most hormones interact with more than one type of receptor e.g. muscarinic lowers BP, but nicotinic increases BP

Question 5

What are the five receptor super families?

Answer 5

1. Integral ion channels
2. Integral tyrosine kinases
3. Steroid receptors
4. G-protein coupled receptors
5. Cytokine receptors

Question 6

How do integral ion channels?

Answer 6

1. 2 agonists bind to receptors
2. Causes opening of pore
3. Allows specific ion movement
4. Causes biological/chemical change

Question 7

How does an integral tyrosine kinase work?

Answer 7

1. Agonist binds
2. Enzyme phosphorylates receptor
3. Causes a change in conformation
4. E.g. insulin

Question 8

How does a steroid receptor?

Answer 8

1. Lipid soluble, so messenger moves through the membrane
2. Binds to receptor inside the cell nucleus
3. Interacts with DNA
4. Promotes/suppresses gene expression

Question 9

How does a G-protein coupled receptor?

Answer 9

1. Agonist binds
2. Interacts with the G-protein
3. Interacts with receptor
4. Releases 2nd messenger
5. Includes sensory receptors
6. G-protein can interact with lots of effectors, allowing for subtlety

Question 10

How does a cytokine receptor work?

Answer 10

1. Agonist binds
2. Causes dimerisation
3. This activates Jak (soluble aterosine kinase)
4. This causes channel phosphorylation
5. Allows for a change
6. E.g. prolactin

Question 11

What are spare receptors?

Answer 11

1. Involves highly effective agonists
2. More receptors means cells are more sensitive to low concentrations of agonist
3. Hence the maximal response from the cell can be produced without all of the receptors binding
4. Could increase agonist affinity

Question 12

What is a partial agonist?

Answer 12

1. These are agonists of low efficacy
2. Means the stimulus is too weak
3. The maximum response of the cell is not reached even when all of the receptor’s binding sites have been bound