glycogen metabolism Flashcards
glycogen definition
intracellular granules, that contain enzymes and proteins
- storage form of glucose utilized in the muscle and liver
glycogen storage form in muscle and liver
muscle: stored in cytoplasm and ER as B-particles
liver: a-particles= larger groups of many B-particles
muscle glycogen function
serves as fuel reserve for the synthesis of ATP within that tissue
- triggered by exercise, leading to oxidation of glucose to produce ATP
liver glycogen function
functions as a glucose reserve for the maintenance of blood glucose levels
- based on available glucose and gluconeogenic precursors
glycogenolysis definition
breakdown of glycogen to glucose or G6P
glycogenesis definition
synthesis of glycogen, from glucose
similarities and differences between glycogenolysis and glycogenesis
-separate metabolic pathways
-share one enzyme in common
- both occur in the cytosol
1st needed enzyme of glycogenolysis
glycogen phosphorylase
- glycogen to (glycogen - 1 residue) + G1P
2nd needed enzyme of glycogenolysis
phosphoglucomutase
- converts G1P to G6P
3rd needed enzyme of glycogenolysis
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
4th needed enzyme of glycogenolysis that is tissue-dependent
liver: glucose 6-phosphatase converts G6P to glucose
muscle: lacks this enzyme, so G6P undergoes glycolysis
glycogen synthesis definition
synthesis of glycogen from G1P, using ATP
- separate pathway from glycogen breakdown
glucokinase/hexokinase in glycogen synthesis
glucose to G6P
- liver: glucokinase
- peripheral tissue: hexokinase
phosphoglucomutase in glycogen synthesis
- G6P to G1P, G1P is then combined w/ UTP to form UDP-glucose
- bc it needs to be high-energy to connect to glycogen
glycogen synthase in glycogen synthesis
creates the alpha 1-4 linkage in glycogen, only can do it to preexisting glycogen chain
glycogenin in glycogen synthesis
protein that initiates glycogen synthesis, by serving as “primer” for glycogen synthase
branching enzyme in glycogen synthesis
removes alpha 1-4 linkage on terminal branch end and forms a new branch
cost of glycogen synthesis
2 ATP molecules per glucose added to glycogen
control of glycogen metabolism
reciprocal control of glycogen synthase and glycogen phosphorylase
muscle glycogen phosphorylase/ glycogen breakdown regulation
activated by AMP and glucagon or epinephrine (cAMP), inhibited by ATP and G6P
glycogen synthase/glycogen synthesis regulation
activated by G6P and insulin, inhibited by AMP and cAMP
when are insulin and glucagon released
- insulin is synthesized in pancreas when glucose in blood is high
- glucagon is synthesized in pancreas when glucose in blood is low
what does glucagon stimulate and where?
glucagon is released from the pancreatic a-cells, and picked up by receptors in the liver, generating intracellular cAMP
