L02: Membrane receptors

Question 1

What are the 4 main types of receptors

Answer 1

• ligand gated ion channels (ionotrophic)
• G protein coupled receptors (metabotrophic)
• nuclear receptors
• kinase linked receptors

Question 2

How do g-protein coupled receptors work

Answer 2

1) an agonist binds to the receptor
2) G proteins that contain alpha , beta and gamma subunit are attached to the proteins
3) nucleotide exchange occurs, so GTP is exchanged with GDP.
4) this activates gpcrs
5) alpha and beta+gamma subunit dissociate
6) alpha subunit is involved in secondary messengers
7) beta + gamma is involved in regulating ion channels
8) alpha subunit hydrolysed GDP back to GTP and everything resets.

Question 3

What are the main alpha subunit types

Answer 3

• Gas
• Gai
• Gaq/11
• Ga12/13

Question 4

What is the role of Gas

Answer 4

Stimulate the production of adenyly cyclase to make CAMP (second messenger)

Question 5

What is the role fo Gai

Answer 5

Inhibit the production of adenyly cyclase so less CAMP is made

Question 6

What is the role of gaq/11

Answer 6

Phospholipase C

Question 7

What is the role of ga12/13

Answer 7

Regulates small G proteins of actin in muscle

Question 8

Explain in detail what Gas does

Answer 8

• Converts ATP to CAMP by adenyly cyclase

- CAMP phosphodiesterase phosphorylates CAMP to degrade it to give AMP and limits the reaction

Question 9

Explain in detail what Gaq/11 does

Answer 9

• stimulates an enzyme - phospholipase C
• Phospholipase C uses phopsholipids in particular PIP2 as a substrate
• this gives DAG and INSP3 (second messengers)
• INSP3 activates channels on the end plastic reticulum that releases calcium for muscle contraction
• DAG converts protein kinase C

Question 10

How can CAMP become involved in glycogen activity after been made from Ga/s

Answer 10

• CAMP activates protein kinase A
• protein kinase A phosphorylates phosphorylase kinase to become active : phosphorylase kinase-p
• phosphorylase kinase p phosphorylates glycogen phosphorylase b to become active glycogen phosphorylase a
• glycogen phosphorylase a phophorlyates glycogen to remove glucose from it.
• protein kinase a phosphorylates glycogen syntrase to inactive p-glycogen syntrase to stop production of glycogen.

Question 11

Which G proteins are involved in muscle contraction

Answer 11

• gas
• Gai
• gaq

Question 12

What are the roles of gas and Gai

Answer 12

Gas activates adenyly cyclase to produce CAMP (second messenger) . CAMP inhibits MLCK so muscle relaxes.
Gai increases MLCK activity so muscle contracts.

Question 13

What is the role of gaq.

Answer 13

Calcium influx so calcium activates MLCK for muscle contraction

Question 14

Is phosphorylation of protein kinase and protein phosphatase reversible or irreversible

Answer 14

Reversible