Bio Lecture 25 Metabolic Signaling

Question 1

What are the two pathways that can be initiated by insulin binding to RTK?

Answer 1

RTK autophosphorylates and phosphorylates IRS-1.

IRS-1 recruits GRB-2 to signal the MAPK pathway. It also recruits PI3-K which activates the AKT pathway.

Question 2

What are the general effects of MAPK and AKT?

Answer 2

MAPK is involved in cell division and survival.

AKT affects muscle and adipose tissue by bringing Glut-4 to the surface to bring in glucose.

Question 3

How does insulin affect PKA?

Answer 3

It increases the activity of a phosphatase that dephosphorylates PKA substrates.
It decreases the activity of PKA by decreasing cAMP.

Question 4

How does glucagon affect PKA?

Answer 4

Glucagon binds to a G-coupled receptor which activates Adenylyl Cyclase and produces cAMP which activates PKA.

Question 5

What do insulin and glucagon do in terms of phosphorylation?

Answer 5

Insulin dephosphorylates

Glucagon phosphorylates

Question 6

What are the two enzymes in the liver that deal with glycogen production and break down?

Answer 6

Glycogen synthase makes it

Glycogen phosphorylase breaks it down

Question 7

What are the insulin counterregulatory hormones?

Answer 7

Glucagon, cortisol, epinephrine, norepinephrine.
Glucagon is released in response to blood glucose levels.
The others are released by neuronal signals in response to stress usually.

Question 8

When is epinephrine released?

Answer 8

Exercise, pain, hypoglycemia, hemorrhage, hypoxia

Question 9

What are the effects of epinephrine?

Answer 9

Tells pancreas to make more glucagon and less insulin.

Signals liver, muscle and adipose to mobilize macro molecules for oxidation.

Question 10

What are the effects of glucagon?

Answer 10

It only affects the liver. Promotes macromolecule breakdown and release of glucose into the blood. Gluconeogenesis from amino acids.

Question 11

Which hormones bind to G-coupled receptors?

Answer 11

Glucagon, epinephrine.

Question 12

What is beta oxidation?

Answer 12

converts fatty acids into acetyl coA and NADH, FADH2

Question 13

How does glucose get into the liver?

Answer 13

GLUT-2 transporter

Question 14

Summarize the actions of insulin, glucagon, epinephrine in the liver.

Answer 14

Insulin: glycogenesis, fatty acid synthesis

Glucagon/epinephrine: Gluconeogenesis, Glycogenolysis, ketogenesis

Question 15

Summarize hormone signaling in adipose tissue.

Answer 15

Insulin: uptake of glucose through GLUT-4, storage of TAGs made in the liver, lipogenesis

Epinephrine: Lipolysis to release fatty acids

Question 16

Summarize hormone signaling in muscle tissue.

Answer 16

Insulin: glucose uptake through GLUT-4 which can also happen through AMPK signaling from high levels of AMP. Does glycogenesis as well for muscle use only.

Epinephrine: glycogenolysis

Question 17

What happens to glucose brought into muscles through AMPK signaling?

Answer 17

It is catabolized and not stored. AMPK is activated my high levels of AMP meaning low energy in the cell.

Question 18

What activates AMPK?

Answer 18

High levels of AMP allosterically interact with AMPK and AMP also indirectly phosphorylates AMPK. Both enhance its activity significantly.

Question 19

What does metformin do?

Answer 19

It decreases ATP production in the mitochondria and thereby increases AMP levels in the cell. This activates AMPK. This brings GLUT-4 to the surface and glucose is taken up. It also decrease gluconeogenesis in the liver.

Question 20

What are the general effects of AMPK?

Answer 20

It shifts metabolic processes from ATP consuming to ATP producing. This means any kind of macromolecule synthesis is turned off and breakdown of molecules happens to produce energy.