Cell Signaling Pathways Insulin

Question 1

what does insulin do

Answer 1

reduce glucose levels

Question 2

what does glucagon do

Answer 2

raises glucose levels

Question 3

what is the most common form of carbohydrates ingested through diet

Answer 3

starch

Question 4

what is the brains main source of energy

Answer 4

glucose

Question 5

what are the types of carbohydrates in nature

Answer 5

polysaccharides, disaccharides, and monosccharides

Question 6

what type of cells release insulin

Answer 6

beta cells

Question 7

what type of cells release glucagon

Answer 7

alpha cells

Question 8

what does phosphrylation do

Answer 8

reversibly turn an enzyme or receptor on or off altering its function

Question 9

where does phosphorylation occur on enzymes or receptors

Answer 9

serine, threonine, tyrosine, and histidine

Question 10

what is a kinase

Answer 10

an enzyme that phosphorylations by adding phosphate residues, uses ATP

Question 11

what is a phosphatase

Answer 11

an enzyme that removes phosphate residues (desphosphorylates)

Question 12

what does insulin do to glycogen synthase

Answer 12

activates protein phosphatase which dephosphorylates glycogen synthase and activates it

Question 13

what does insulin do to glycogen phosphorylase

Answer 13

it activates protein phosphatase and dephosphorylates glycogen phosphorylase which inhibits it

Question 14

what does glucagon do to glycogen synthase

Answer 14

it uses cAMP to activate protein kinase A which phosphorylates glycogen synthase which inactivates it

Question 15

what does glucagon do to glycogen phosphorylase

Answer 15

it uses cAMP to activate phosphorylase kinase which phosphorylates glycogen phosphorylase which activates it

Question 16

what happens in insulin biosynthesis

Answer 16

proinsulin is cleaved into insulin and C peptide

Question 17

describe how insulin is released by the pancreas

Answer 17

-glucose is transported into beta cells by GLUT 2
-glucose goes into the glycolytic pathway to make ATP
- an increase ATP: ADP ration closes K+ channel causing depolarization
-this causes Ca2+ channels to open and Ca2+ stimulates the exocytosis of stored insulin. it also actives insulin gene expression via CREB

Question 18

what is normal fasting blood glucose

Answer 18

70-130 mg/dL

Question 19

describe the insulin receptor

Answer 19

a transmembrane receptor composed of alpha and beta subunits that belong to the family of tyrosine kinase receptors

Question 20

what binds to and activates insulin receptors

Answer 20

IGF 1, IGF 2, and insulin

Question 21

what happens when a ligand binds to the alpha chains of the insulin receptor

Answer 21

causes a conformational change that leads to autophosphorylation of tyrosine residues within the intracellular domain of the beta chain

Question 22

what is the affinity of insulin receptors for insulin

Answer 22

high

Question 23

what does the beta isoform of the insulin receptor bind

Answer 23

only insulin

Question 24

what does the alpha isoform of the insulin receptor bind

Answer 24

IGF and insulin

Question 25

what happens to GLUT4 when insulin binds to a receptor

Answer 25

GLUT4 secretory vesicles move GLUT4 receptors to the membrane

Question 26

what does SGLT1 do

Answer 26

-mediates intestinal absorption of glucose from the diet on the luminal side of the intestinal enterocyte
- important in the glucose mediated secretion of incretin hormones, GIP and GLP 1

Question 27

what does the GLUT2 receptor do

Answer 27

important for basolateral efflux of glucose into the blood stream

Question 28

what are incretin hormones

Answer 28

gut hormones released after eating that stimulate the secretion of insulin by the beta cells of the pancreas

Question 29

what are the major incretin hormones

Answer 29

GLP 1 and GIP

Question 30

what are GLP 1 and GIP inactivated by

Answer 30

DPP 4 which is released from endothelial cells of blood vessels

Question 31

what type of enzyme is the DPP 4 inhibitor

Answer 31

serine protease

Question 32

what do DPP 4 inhibitors do

Answer 32

lead to increased insulin secretion and decreased glucagon levels and consequently improvement in hyperglycemia

Question 33

describe the mechanism of action of GLP 1RAs and DPP4 inhibitors

Answer 33

oral intake of glucose get absorbed by the small intestine brush border. this increases GLP 1 and GIP. this binds to GLP 1RA in the beta cell which triggers the release of insulin and glucose uptake in fat and muscle . DPP4 also binds to GLP 1 and GIP in alpha cells to decrease glucagon and glucose production in the liver

Question 34

how does insulin regulate lipolysis (lipid metabolism)

Answer 34

• glucose enters the beta cell which causes insulin release. insulin then binds to a receptor on an adipocyte. this causes a kinase cascade that causes phosphodiesterase to convert cAMP to AMP so fatty acids are not created and released

Question 35

what happens to glucose levels when fatty acid levels are high

Answer 35

glucose levels are low and vice versa

Question 36

how does acetyl- CoA carboxylase regulate FA metabolism

Answer 36

dephosphorylation of ACC stimulates production of precursors for fatty acid synthesis and one of these precursors, Malonyl CoA inhibits fatty acid beta oxidation

Question 37

what adpator proteins does signaling via the insulin receptor involve

Answer 37

IRS 1 and IRS2 which transduce the signal via AKT and MAP kinases to effect changes in metabolic enzyme activity and gene expression

Question 38

what is the effect of persistent hyperglycemia

Answer 38

damages number of tissues and organs

Question 39

aside from blood glucose levels, what else does insulin affct

Answer 39

increases the rate of lipogenesis and glycogen synthesis to store glucose as glycogen or fatty acids

Question 40

why does the brain use glucose as an energy source instead of fatty acids

Answer 40

• ATP generation from beta oxidation of fatty acids uses more oxygen than glucose which increases the risk of the cells becoming hypoxic
• beta oxidation of fatty acids generates superoxide which puts neurons under severe oxidative stress
• ATP generation from fatty acids stored in fat is slower than using blood glucose for fuel