glycogen Flashcards
Energy sources during exercise over time
1) ATP + creatine phosphate
2) anaerobic glycolysis of muscle glycogen
3) Anaerobic oxidation of muscle glycopgen, liver glycogen, plasma glucose
4) Aerobic oxisation of plasma FFA and plasma tissue triglycerides.
Enzymes needed for glycogen synthesis
glycogen synthase: adds glucosyl units in an alpha 1,4 linkage
Branching enzymes ads glucosyl units in an alpha 1,6 linkage
Enymes required for glycogen degradation
glycogen phosphorylase- removed glucosyl units from alpha 1,4 linkage
debranching enzyme- transferase and alpha 1,6-glucosidase
Phosphorylase a regulators
Phosphorylase a is the phosphorylated and active form that causes degradation of glycogen.
activators: cAMP, PI, Ca2+. cause activation of PKA which P and activates phos a. glucagon
inhibitors: insulin, ATP
when glucose and ATP levels are high (necrosis, inflammation, liver injury) tney can bind directly to the phosphorylated form and inactivate it.
phosphorylase b regulators
inactive form that promotes glycogen synthesis. it is dephosphorylated
Activators: insulin
inhibitors: cAMP
AMP can bind directly to the b enzyme, causing a conformational change an activate from b to a form. regardless of phosphorylation status
glycogen synthase a
this is the active dephosphorylated form. glyccogen synthesis
promotors: insulin
inhibitors: cAMP
glycogen synthase b
this is the inactive phosphorylated form. no glycogen formation.
promotors: cAMP, PKA, calmodulin dependent protein kinase, PKC, caesin kinase, glucose-6-phosphate, glucagon
inhibitors: glycogen synthase kinase 3, insulin
under certain circumstances like pathological GSD, when glucose-6-P is high it directly binds to the b forms causing a conformational change to activate it.
Fasted state phophorylase and synthase
Phosphorylase a: P, active, glucagon, relaxed, glycogen degradation, high affinity to glycogen. inhibited by high glucose and ATP
Synthase b: P, inactive, glucagon, tight, substrate is UDP glucose, low affinity to substrate. inhibited by G-6-P which promotes synthesis of glycogen.
Fed state phosphorylase and synthase
Phosphorylase b: dephosphorylated, inactive form. low affinity to substrate, won’t degrade glycogen. promoted by insulin. inativated during high energy levels. when energy levels drop, have high AMP, activated form promoted for glycogen degradation.
Synthase a: dephosphorylated, active form. promotes glyocogen synthesis. promoted by insulin.
Effects of cAMP in liver
1) promotes glycogen degradation
2) inhibits glycolysis
3) inhibits glycogen synthesis
all promoted by glucagon
Effects of cAMP in heart and muscle
only activated by epi not glucagon
1) promotes glycogen degradation
2) Activates glycolysis
3) inhibits glycogen synthesis
PI in the liver
Epi activates this pathway
1) IP3 increases calcium
2) Ca2+ activates a Ca2+ depdendent PK
3) DAG activates PKC
stimulation of glycogenolysis by alpha agonists. inhibition of glycogen formation
Ca2+ in the muscle
pathway activated by nerve impulses on an AcH receptor, causes depolarization and release of Ca+.
Ca 2+ causes glycogen degradation. forma lactate
insulin in muscle cells
activates kinase mediated signaling cascade. causes uptake of glucose by GLUT 4. Promoted glycogen formation and inhibits glycolysis
Insuline in liver cells
kinase mediated signaling causes uptake of glucose. promotes glycogen formation and inhibits glycolysis.
