Regulation fof Carbohydrate Metabolism

Question 1

what are the 5 mechanisms of hormone regulation?

Answer 1

1. induction/repression
2. covalent regulation (reversible phosphorylation)
3. allosteric regulation
4. isozymes
5. substrate supply regulation

Question 2

how does induction/repression work in metabolism?

Answer 2

glucose-6-phosphate dehydrogenase is induced by insulin

repressed by glucagon

Question 3

how does covalent regulation work in metabolism?

Answer 3

dephosphorylation promoted by insulin in fed state by phosphatases
phosphorylation promoted by glucagon in fasting state by cAMP/PKA pathway

Question 4

what is normal blood glucose?

Answer 4

70-100 mg/dl

Question 5

where does insulin come from?

Answer 5

pancreas

Question 6

how does allosteric regulation work in metabolism?

Answer 6

• ratio of ATP/ADP- want it high, if it drops, stimulates ATP producing pathways
• ratio of NAD/NADH- want it high, if it drops then NADH producing steps are inhibited
• citrate- builds up when TCA cycle is inhibited
• acetyl CoA- from fatty acid oxidation
• alanine- from protein/amino acid catabolism

Question 7

what isozymes are involved in metabolism?

Answer 7

hexokinase in muscle

glucokinase in liver

Question 8

how is the substrate supply regulated?

Answer 8

• glucose transport into insulin sensitive tissues
• release of glucose from glycogen
• release of fatty acids from adipose TAGs

Question 9

what does insulin do?

Answer 9

• increases glucose uptake into muscle and adipose via GLUT4 transporters
• turns on pathways that use glucose (glycolysis, storage)
• turns off endogenous fuel production (glucose release from storage)

Question 10

is liver sensitive to insulin?

Answer 10

No- glucose uptake increases when glucose is very high in blood

Question 11

what are the 3 regulated steps of glycolysis?

Answer 11

glucokinase
phosphofructokinase
pyruvate kinase

Question 12

how is glucokinase regulated?

Answer 12

• only favors glucose–>glucose-6-phosphate when glucose concentration is high
• glucose promotes movement of GK from nucleus to cytoplasm

Question 13

what is the rate limiting step of glycolysis?

Answer 13

phosphofructokinase 1

Question 14

how is PK1 regulated?

Answer 14

allosteric interactions
activated by: AMP and fructose-2-6-bisphosphate
inhibited by: ATP and citrate

Question 15

how is pyruvate kinase regulated?

Answer 15

induced by insulin
inhibited by: ATP and alanine, phosphorylation
activated by: fructose 1,6 bisphosphate (feedforward activation), dephosphorylation by insulin’s phosphatase

Question 16

what is the primary regulation of glycogen synthesis?

Answer 16

reversible phosphorylation

Question 17

when do you want glycogen made? when do you not want glycogen made?

Answer 17

make it when glucose is abundant (store glucose)

don’t make it when glucose is low (use glucose)

Question 18

how is glycogen synthesis regulated?

Answer 18

reversible phoshporylation

Question 19

what does insulin do to glycogen synthase?

Answer 19

dephoshporylates it–activates–>glycogen synthesis

Question 20

what does glucagon do to glycogen synthase?

Answer 20

phosphorylates it–deactivates–>glycogen breakdown

Question 21

what stimulates addition of a phosphate to glycogen synthase?

Answer 21

PKA, PKC stimulate phosphorylase kinase- adds phosphate to glycogen synthase

Question 22

what inhibits addition of phosphate to glycogen synthase

Answer 22

insulin inhibits glycogen synthase kinase`

Question 23

what stimulates removal of a phosphate from glycogen synthase?

Answer 23

insulin activates phophoprotein phosphatase

Question 24

what inhibits removal of a phosphate from glycogen synthase?

Answer 24

cAMP inhibits phosphoprotein phosphatase