Lecture 22

Question 1

Explain the process of epinephrine binding to a beta-adrenergic receptor?

Answer 1

1. epinephrine binds to the receptor
2. The occupied receptor leads to displacement of GDP to GTP, thus activating Gs
3. Gs subunit moves to adenylyl cyclase and activates it
4. adenylyl cyclase catalyzes the formation of cAMP
5. PKA (protein kinase A) is activated by cAMP
6. PKA phosphorylates cellular proteins, which leads to a cellular responce
7. cAMP is degraded, thus deactivation of PKA

Question 2

What is the generally happens when glucagon binds to the glucagon receptor?

Answer 2

1. ligand binding
2. Gs (alpha) activation
3. adenylate cyclase activation
4. increased production of cAMP
5. activates PKA
6. protein cascade

Question 3

What kind of receptor is the glucagon receptor?

Answer 3

Beta-adrenergic receptor

Question 4

What are the step to adenylate cyclase activation?

Answer 4

1. Ligand binds to the G-protein receptor
2. The activated receptor interacts with the G-protein and the G alpha subunit is released by phosphorylation
3. GTP bound G alpha subunit activates adenylate cyclase

Question 5

What does adenylate cyclase do exactly?

Answer 5

catalyzes the reaction of ATP to cAMP

Question 6

What does cAMP do?

Answer 6

it binds to protein kinase A and activates it

Question 7

Where is the phosphate group placed on the protein?

Answer 7

Either serine or theronine

Question 8

How is the signal terminated?

Answer 8

1. GTP gets converted back to GDP by GTPase
2. Phosphodiesterase enzyme hydrolyzes cAMP to AMP
3. ligand dissociates from receptor

Question 9

What molecules inhibit inhibit cyclic nucleotide

phosphodiesterase and prolong effects of cAMP?

Answer 9

Caffeine and theophylline

Question 10

How does cAMP impact gene regulation?

Answer 10

cAMP phosphorylates CREB to CREB-P, which can then enter the nucleus and impact gene expression

either decrease or increase expression

Question 11

what does the binding of a ligand to the alpha-2-adrenergic receptor do?

Answer 11

This activates the Gi (alpha)

this inhibits adenylate cyclase

reduces cAMP levels

Question 12

What does ADP-ribosylation do?

Answer 12

leads to the inactivation of target proteins

Question 13

Explain what the cholera toxin does?

Answer 13

Leads to the continuous activation of the Gs alpha protein

Thus the cell has a constant level of cAMP in the cell

This leads to the CFTR channel always being open

result:
watery diarrhea

Question 14

Explain what the pertussis toxin does?

Answer 14

The Gi alpha protein is continuously inactive

Thus increased levels of cAMP in respiratory cells

result: whooping cough

Question 15

Explain the alpha-1-adrenergic receptor pathway?

Answer 15

1. epinephrine or norepinephrine bind to the receptor
2. This activates Gq alpha
3. That G-protein activates phospholipase C
4. That forms the second messengers (IP3, Ca, and DAG)
5. Activates protein kinase C

Question 16

What does phospholipase C do?

Answer 16

This enzyme cleaves PIP2 into IP3 and DAG

Question 17

What does the IP3 protein do?

Answer 17

This protein leads to the release of Ca from the ER

Question 18

cGMP does what?

Answer 18

Second messenger in smooth muscle relaxation,

platelet aggregation and in visual system

Question 19

What is the important of nitric oxide (NO)

Answer 19

Activates Protein kinase G which phosphorylates various proteins

Vascular smooth muscle relaxation by leading to
phosphorylated myosin light chain kinase and inhibits it

vasodilation

Question 20

What is the pathway of NO?

Answer 20

1. activates guanylate cyclase
2. increase cGMP levels
3. activates protein kinase G
4. vasodilation