Signal Transduction

Question 1

Describe the signal transduction pathway of insulin

Answer 1

Insulin binds to alpha subunit of IR
Auto phosphorylated beta subunit of IR
which phosphorylated IRS-1
Which activates PI3K which converts PIP2 to PIP3
Which activates PDK1
Which activates PKB

Question 2

What is the effect of PKB

Answer 2

Inhibits the inhibition of GLUT4 translocation and glycogen synthase

Question 3

How does PKB inhibit the inhibition of GLIT4 translocation

Answer 3

Phosphorylated AS160, which typically inhibits GLUT4 translocation, so this can now happen

Question 4

How does PKB inhibit the inhibition of glycogen synthase

Answer 4

Phosphorylated GKycogen synthase kinase-3 (GSK-3)
So GSK-3 cannot phosphorylate and inactivate glycogen synthase
Glycogen synthase remains active

Question 5

In what form is glycogen synthase active

Answer 5

Dephosphorylated

Question 6

Describe the signal transduction pathway for glucagon

Answer 6

Glucagon binds to GPCR
G alpha subunit is energised and binds to adenylate cyclase, activating it
Adenylate cyclase converts ATP tomcAMP
cAMP activates PKA

Question 7

What is the action of PKA

Answer 7

Activates glycogen phosphorylase
Inactives glycogen synthase

Question 8

How does PKA activate glycogen phosphorylase

Answer 8

Phosphorylated and actives phosphorylase kinase
Which phosphorylated and actives glycogen phosphorylase

Question 9

How does PKA inactive glycogen synthase

Answer 9

Phosphorylates IP/PP1-I which activates it
Binds to PP1 which inactives it
So PP1 cannot dephosphorylate glycogen synthase and activate it

Question 10

What pathway is activated by adrenaline

Answer 10

Also acts via the GPCR – Gαs AC – cAMP – PKA pathway
Specific β-adrenergic receptor (α-adrenergic receptors initiate PKC pathway)

Question 11

What form is glycogen phosphorylase active

Answer 11

Phosphorylated