G-protein linked receptors

Question 1

How many times does a G-protein-linked receptor pass through a membrane?

Answer 1

Passes through 7 times, and so is a seven-pass transmembrane protein

Question 2

Describe a G-protein-linked receptor structurally.

Answer 2

• seven-pass transmembrane protein
• extracellular domain containing hormone binding site
• intracellular domain which contains binding site for a heterotrimeric G-protein, which couples the receptor to targets (commonly ion channels or enzymes)

Question 3

Three subunits of Heterotrimeric G-proteins

Answer 3

alpha
beta
gamma

Question 4

How are heterotrimeric G-proteins molecular switches?

Answer 4

GDP bound to alpha subunit = G-protein is “switched off”

GTP bound to alpha subunit = G-protein is “switched on” and dissociates into 2 parts

• alpha subunit = carries GTP and mediates most signaling
• beta gamma subunits= only recently recognized as a signaling molecule

G-protein will “switch off” after a few seconds by hydrolyzing GTP to GDP. Alpha subunit is thus “switched off” and rejoins with beta gamma subunit

Question 5

G-protein linked second messenger pathway

Receptor -> Gs -> cAMP increase ->

Answer 5

protein kinase A increase

Question 6

G-protein linked second messenger pathway

Receptor -> Gi -> cAMP decrease->

Answer 6

protein kinase A decrease

Question 7

G-protein linked second messenger pathway

Receptor -> Gq -> IP3/DAG ->

Answer 7

Protein Kinase C

Question 8

G-protein linked second messenger pathway

Receptor -> Gq -> NO/cGMP ->

Answer 8

Protein Kinase G

Question 9

If

This is I with a subscript f…

Answer 9

• funny current

- drives potential toward threshold

Question 10

ICa,L

This is I with subscript Ca,L…

Answer 10

• L-type Ca2+ current

- activates at threshold and generates the action potential

Question 11

Norepinephrine released from sympathetic nerve fibers ____________ If and ICa,L, which _________ the frequency

Answer 11

stimulates; increases

Question 12

Acetylcholine released from parasympathetic nerve fibers ___________ If and ICa,L, which ____________ the frequency.

Answer 12

inhibits; decreases

Question 13

Sympathetic Innervation

of cardiac pacemaker in sinus node

Answer 13

• Norepinephrine
• beta 1 receptors
• stiumlation of If and ICa,L
• increases heart rate

Question 14

Parasympathetic Innervation of cardiac pacemaker in sinus node

Answer 14

• acetylcholine
• M2 receptors
• Inhibition of if and ICa,L
• decreases heart rate