L6 - GPCRs 2

Question 1

What are effectors?

Answer 1

Enzymes which activate secondary messengers in the cell either directly or indirectly

Question 2

What are Gi effectors?

Answer 2

-Gi effectors: inhibit adenylyl cyclase, open potassium channels and close calcium channels

Question 3

What are Gq effectors?

Answer 3

-Gq effectors: activate phospholipase C-beta to produce IP3, which release calcium

Question 4

What are examples of secondary messengers? (3)

Answer 4

-Hydrophobic lipids confined to membrane where they are generated
-Small soluble molecules that diffuse through cytoplasm e.g. cAMP
-Calcium ions

Question 5

What are the steps in the cAMP secondary messenger system? (6)

Answer 5

1) Ligand binds to receptors activating G protein
2) Alpa-subunit moves and binds to adenylyl cyclase in membrane
3) Activated enzyme catalyses formation of a cAMP from ATP
4) cAMP activates PKA
5) PKA phosphorylates and activates protein
6) Initiates response within cell

Question 6

What is an example of cAMP secondary messenger system?

Answer 6

-beta2 adrenoreceptor regulation of metabolism

Question 7

Describe the cGMP secondary messenger system?

Answer 7

Similar to cAMP except:
-Enzyme is guanylate cyclase which can be receptor bound or free in cytoplasm
-Converts guanosine triphosphate (GTP) to cGMP

Question 8

What are the 2 types of messenger that are generated from hydrophobic lipids in the membrane? (2)

Answer 8

-Water soluble and diffuse through the cytoplasm e.g. IP3
-Hydrophobic molecules, which remains in the membrane e.g. DAG

Question 9

What does DAG do?
What does IP3 do?

Answer 9

-DAG stays in the membrane and activates protein kinase 3
-IP3 diffuses through cytoplasm and the target is the calcium channel that resides on the intracellular membrane on endoplasmic reticulum

Question 10

What is an example of hydrophobic lipids in the membrane as secondary messengers?

Answer 10

phospholipase C-beta

Question 11

How is the target of phospholipase C-beta created?

Answer 11

-When DAG binds it causes dissociation and creates a target for the target proteins

Question 12

What are 5 processes regulated by calcium signalling? (5)

Answer 12

1) Synaptic transmission
2) Hormone secretion and synthesis in some cases
3) Fertilisation
4) Muscle contraction
5) Cytokinesis

Question 13

Howe are calcium levels regulated?

Answer 13

-Calcium pumps (powered by ATP)

Question 14

What amplifies the signal of IP3 in calcium signalling?
what does the IP3 then activate

Answer 14

-ORAI
-STIM protein that acts as ligand and opens channel to let Ca2+ flow

Question 15

What is used for calcium imaging?

Answer 15

Fluorescent molecules such as GFP