Metabolic effect of Insulin / Glucagon

Question 1

Structure of Insulin

Answer 1

51 AAs in 2 polypeptide chains, A and B
2 disulfide bridges
intramolecular sulfide bridge between AA residues in the A chain

Question 2

Insulin synthesis location

Answer 2

beta cells of islets of Langerhans

Question 3

Pathway of insulin maturation

Answer 3

Preproinsulin ->ER -> Proinsulin -> Glogi -> Insulin + Cpeptide

Question 4

Insulin degradation

Answer 4

in liver, kidney
by INSULINASE
halflife 6 min

Question 5

Regulation of Insulin secretion

Answer 5

increased by: glucose, AAs, gastrointestinal hormones (CCK, gastric inhibitory polypeptide)
decreased by: epinephrine

Question 6

Metabolic effects of insulin

Answer 6

glucose metabolism:
-storage in muscle, liver, adipocytes
-glycogen synthesis in liver, muscle
-inhibits glycogenolysis, gluconeogenesis in liver
lipid metabolism: 
-decrease TAG degeneration
-increase TAG synthesis
protein synthesis

Question 7

Insulin receptor

Answer 7

alpha and beta subunits- tetramer
B: hydrophobic domain spans plasma membrane
A: extracellular- insulin binding site
B: cytosolic domain - tyrosine kinase

Question 8

Signal transduction of Insulin

Answer 8

insulin binds to alpha subunit
conformational change to beta subunits
autophosphorylation
phosphorylation of insulin receptor subunits

Question 9

Structure of Glucagon

Answer 9

29AAs in single polypeptide chain

Question 10

Glucagon synthesis location

Answer 10

alpha cells of islets of Langerhans

preproglucagon -> glucagon

Question 11

Regulation of Glucagon secretion

Answer 11

Increased by:low blood glucose, AAs, epinephrine

Decreased by: high blood glucose

Question 12

Metabolic effects of Glucagon

Answer 12

Carbohydrate metabolism: breakdown in liver
Lipid metabolism: lipolyis
Protein metabolism: uptake of AA in liver

Question 13

Mechanism of Glucogon

Answer 13

bind to G protein coupled receptor
activation of adenylyl cyclase
rise of cAMP
activates cAMP dependent protein kinase
phosphorylation