glycogen metabolism Flashcards
what is glycogen?
- branched polymer of glucose, readily mobilizable form of storage
- most glycogen is found in the muscles
what is the function of glycogen?
- energy production in muscles
- maintain blood glucose level by liver (only liver releases glucose into blood)
where does glycogen metabolism occur?
- cytosol
- present in most cell types
- glucose-6-phosphate only present in liver (required for glucose export)
what is the rate limiting enzyme of glycogen synthesis?
glycogen synthase
what is the rate limiting enzyme of glycogen breakdown?
glycogen phosphorylase
what is the feedback cycle of glycogen metabolism in a fed state? (3)
- high glucose→ high ATP→ high insulin→ activates glycogen synthesis, inactivates glycogen phosphorylase
- high glucose→ high G6P→ activates glycogen synthase→ INCREASE glycogen synthesis
- glucose, G6P, ATP inhibit glycogen phosphorylase→ DECREASE glycogen breakdown
what is the feedback cycle of glycogen metabolism in a fasting/exercise state?
- increase glucagon/epinephrine→ activate phosphorylase, inhibit synthase
- AMP/Ca2+→ activates glycogen phosphorylase→ increase glycogen breakdown
how is glycogen metabolism regulated in high energy need?
high energy state→ fall ATP→ increase AMP, increase Ca→ activate glycogen phosphorylase→ increase breakdown, decrease synthesis
how is glycogen metabolism regulated in low energy need?
low energy need→ high ATP, high G6P→ increase synthesis, decrease breakdown
what is the relation of DM to glycogen metabolism?
DM: insulin deficiency→unopposed glucagon action even in fed state→ activates glycogen breakdown→ increase glucose
what glycogen storage disease type affects glycogen synthesis?
only type 4 (andersen)
what are the glycogen storage disease types that affect glycogen breakdown?
types 1, 2, 3, 5
what is von gierke (type 1) glycogen storage disease? (enzyme + organ)
- deficiency of glucose 6 phosphatase
- G6P accumulates in liver/kidneys
what are the manifestations of von gierke (type 1) and cori (type 3) diseases?
- fasting hypoglycemia
- organomegaly
- type1: lactate/uric acid accumulation
what is pompe disease (type 2)? (enzyme + organ)
- deficiency of 1-4 glucosidase (debranching enzyme in LYSOSOMES)
- esp affects heart→ cardiac failure/cardiomegaly