Major Receptor Families

Question 1

What is the richest source of receptors

Answer 1

Membrane bound proteins

Question 2

What are the 4 majour families of receptors

Answer 2

1) Ligand- gated ion channels (eg. Cholinergic ion channels)
2) G- protein coupled receptors (eg. a and B receptors)
3) enzyme- linked receptors (eg. Insulin receptors)
4) intracellular receptors (eg.steroid receptors)

Question 3

How do transmembrane ligand gated ion channels work

Answer 3

The channel is always closed until it is bound to an agonist then is is open for a few seconds

Question 4

What does the response of an ion gated channel depend on?

Answer 4

The ions conducted through the channels

Question 5

What does stimulation of nicotinic receptors lead to

Answer 5

By stimulation with acetylcholine channels open allowing the influx of sodium and Efflux of potassium across the cell membrane generating an action potential

Question 6

What happens after the activation of GABA receptors

Answer 6

Cl- influx resulting in hyper polarisation

Question 7

What happens when a local anaesthetic binds to voltage gated channels

Answer 7

Inhibition of ana+ influx and decrease in neuronal transmission

Question 8

How do G protein coupled receptors work

Answer 8

They are composed of 3 subunits, a subunit binds to GTP and B and y anchor the G- protein in the cell membrane, what an agonist binds to the G protein causes the increase in GTP binding to a subunit causing dissociation of the a-GTP complex and By complex’s, these complexes are then free to interact with cellular effectors

Question 9

What are the subtypes of G-proteins

Answer 9

Gs
Gi
Gq

Question 10

How does Gs work

Answer 10

Gs - activates adenylyl cyclase -> increases camp

Question 11

How does Gi G protein work

Answer 11

Gi inhibits adenylyl cyclase -> decreasing camp

Question 12

How does Gq G protein work

Answer 12

Gq - activates phosphlipase C -> generating IP3 and DAG

Question 13

What does IP3 from Gq do

Answer 13

IP3 increases cellular calcium —> activating protein kinase

Question 14

How does DAG from Gq work

Answer 14

DAG similar to CAMP activates specific protein kinases

Question 15

a1,a2,B1,B2

Answer 15

QISS

Question 16

M1,M2,M3

Answer 16

QIQ

Question 17

How long does G protein channel last

Answer 17

Several seconds to minutes

Question 18

How long does enzyme linked receptors last

Answer 18

Minutes to hours

Question 19

What do the most common enzyme linked receptors have

Answer 19

Tyrosine kinase

Question 20

What’s the mechanism of action of enzyme linked receptors

Answer 20

Phosphorylation of tyrosine residues with the help of tyrosine kinase in turn activate phosphorylates target protein creating a cascade similar to G proteins

Question 21

How does the ligand reach intracellular receptors

Answer 21

It must have enough lipophilictiy to pass through the cell membrane

Question 22

What is the primary target of activation of intracellular receptors

Answer 22

Transcription factors in the nucleus

Question 23

How long does it take for intracellular receptors need to show their activity

Answer 23

Hours to days

Question 24

What is signal amplification characteristic of

Answer 24

Enzyme linked receptors and G protein coupled receptors

Question 25

What is the result of signal amplification

Answer 25

Not all receptors need to be bound in order to elicit a maximal response

Question 26

What are spare receptors and give examples of them

Answer 26

Systems which don’t need to bind to all receptors in order to elicit a maximal response are said to have spare receptors
Eg. 5-10% of B receptors in the heart are spare
99% of insulin receptors are spare

Question 27

Why does desensitisation occur

Answer 27

Due to too much agonists activity resulting in diminished response

Question 28

What is tachyphylaxis

Answer 28

Another name for desensitisation and it occurs due to phosphorylation causing receptors unresponsive to agonists

Question 29

What does too much agonistic activity lead to

Answer 29

Down regulation

Question 30

What does too much antagonist activity lead to

Answer 30

Up regulation can make cells more responsive to agonist and less to antagonist

Question 31

What is a refractory period

Answer 31

After receptors activation, some receptors (i.e ion channels) require some time before they get activated again