glycogen metabolism

Question 1

glycogen definition

Answer 1

intracellular granules, that contain enzymes and proteins
- storage form of glucose utilized in the muscle and liver

Question 2

glycogen storage form in muscle and liver

Answer 2

muscle: stored in cytoplasm and ER as B-particles
liver: a-particles= larger groups of many B-particles

Question 3

muscle glycogen function

Answer 3

serves as fuel reserve for the synthesis of ATP within that tissue
- triggered by exercise, leading to oxidation of glucose to produce ATP

Question 4

liver glycogen function

Answer 4

functions as a glucose reserve for the maintenance of blood glucose levels
- based on available glucose and gluconeogenic precursors

Question 5

glycogenolysis definition

Answer 5

breakdown of glycogen to glucose or G6P

Question 6

glycogenesis definition

Answer 6

synthesis of glycogen, from glucose

Question 7

similarities and differences between glycogenolysis and glycogenesis

Answer 7

-separate metabolic pathways
-share one enzyme in common
- both occur in the cytosol

Question 8

1st needed enzyme of glycogenolysis

Answer 8

glycogen phosphorylase
- glycogen to (glycogen - 1 residue) + G1P

Question 9

2nd needed enzyme of glycogenolysis

Answer 9

phosphoglucomutase
- converts G1P to G6P

Question 10

3rd needed enzyme of glycogenolysis

Answer 10

glycogen debranching enzyme
- glycogen phosphorylase is specific to alpha 1,4-glycosidic linkages but stop 4 residues before branch
- so then glycogen debranching enzyme works from there

Question 11

4th needed enzyme of glycogenolysis that is tissue-dependent

Answer 11

liver: glucose 6-phosphatase converts G6P to glucose
muscle: lacks this enzyme, so G6P undergoes glycolysis

Question 12

glycogen synthesis definition

Answer 12

synthesis of glycogen from G1P, using ATP
- separate pathway from glycogen breakdown

Question 13

glucokinase/hexokinase in glycogen synthesis

Answer 13

glucose to G6P
- liver: glucokinase
- peripheral tissue: hexokinase

Question 14

phosphoglucomutase in glycogen synthesis

Answer 14

• G6P to G1P, G1P is then combined w/ UTP to form UDP-glucose
• bc it needs to be high-energy to connect to glycogen

Question 15

glycogen synthase in glycogen synthesis

Answer 15

creates the alpha 1-4 linkage in glycogen, only can do it to preexisting glycogen chain

Question 16

glycogenin in glycogen synthesis

Answer 16

protein that initiates glycogen synthesis, by serving as “primer” for glycogen synthase

Question 17

branching enzyme in glycogen synthesis

Answer 17

removes alpha 1-4 linkage on terminal branch end and forms a new branch

Question 18

cost of glycogen synthesis

Answer 18

2 ATP molecules per glucose added to glycogen

Question 19

control of glycogen metabolism

Answer 19

reciprocal control of glycogen synthase and glycogen phosphorylase

Question 20

muscle glycogen phosphorylase/ glycogen breakdown regulation

Answer 20

activated by AMP and glucagon or epinephrine (cAMP), inhibited by ATP and G6P

Question 21

glycogen synthase/glycogen synthesis regulation

Answer 21

activated by G6P and insulin, inhibited by AMP and cAMP

Question 22

when are insulin and glucagon released

Answer 22

• insulin is synthesized in pancreas when glucose in blood is high
• glucagon is synthesized in pancreas when glucose in blood is low

Question 23

what does glucagon stimulate and where?

Answer 23

glucagon is released from the pancreatic a-cells, and picked up by receptors in the liver, generating intracellular cAMP