3.3

Question 1

3 essential components that define GPCR signal transduction

Answer 1

1.receptor in membrane with 7 transmembrane spanning helices
2. G protein that cycles between active GTP and inactive GDP
3. effector enzyme

Question 2

Steps of GPCR signaling

Answer 2

1. specific ligand binds to GPCR to activate the receptor
2. GPCR interacts with a G protein which exchanges GDP for GTP
3. The active GTP-bound G protein dissociates from receptor complex and binds to nearby effector enzyme or ion channel to alter its activity
4. Effector enzyme or ion channel generates a second messenger signaling molecule that affects downstream targets

Question 3

What is beta adrenergic receptor and steps?

Answer 3

-a GPCR that binds epinephrine (adrenaline)
1. Epinephrine binds to receptor
2. GDP turns to GTP
3. GTP activates Adenylyl cyclase
4. Adenylyl cyclase activates cAMP
5. cAMP activates PKA
6. PKA phosphorylation causes epinephrine response
7. cAMP is degraded, PKA is blocked again

Question 4

What does Adenylyl cyclase do?

Answer 4

Turns ATP into cAMP

Question 5

why is cAMP important for the beta adrenergic receptor?

Answer 5

-acts as a 2nd messenger by binding to and activating protein kinase A (PKA)

Question 6

Protein Kinase A

Answer 6

-activated by binding to cAMP when cAMP levels increase
-stimulates glycogen breakdown and releases D-glucose

Question 7

What happens when there are low cAMP levels?

Answer 7

-2 regulatory subunits block substrate binding clefts and PKA is inhibited

Question 8

What happens when there are high levels of cAMP?

Answer 8

-regulatory subunits bind to cAMP
-substrate binding sites are no longer blocked

Question 9

How does epinephrine stimulate the release of glycogen?

Answer 9

PKA Phosphorylation does 2 things
1. promotes glucose release
2. Inhibits glycogen synthesis

Question 10

What 2 proteins shut off epinephrine signaling?

Answer 10

-Beta-adrenergic receptor kinase (BARK)
-Beta-arrestin

Question 11

Rods

Answer 11

-Sense low levels of light
-can’t differentiate color

Question 12

Cones

Answer 12

-3 subtypes
-can differentiate color

Question 13

What is the chromophore in rhodopsin?

Answer 13

11-cis-retinal

Question 14

How does light activate rhodopsin?

Answer 14

When 11-cis-retinal absorbs light, its conformation changes to trans-retinal
-this shape change causes G protein to be activated

Question 15

GPCR signaling motif?

Answer 15

Receptor–>G-protein–>Effector

Question 16

Rhodopsin signaling?

Answer 16

Receptor: Rhodopsin
G-protein: transducin
Effector: PDE

Question 17

Transducin

Answer 17

G-protein with 3 subunits and activates PDE

Question 18

How does cyclic GMP regulate rod/cone ion channels?

Answer 18

-In the dark: cGMP is at high level–>channel is open–>inactive rhodopsin
-In the light: cGMP levels drop–>channel is closed–>active rhodopsin