glycogen metabolism Flashcards

1
Q

what is glycogen?

A
  • branched polymer of glucose, readily mobilizable form of storage
  • most glycogen is found in the muscles
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2
Q

what is the function of glycogen?

A
  1. energy production in muscles
  2. maintain blood glucose level by liver (only liver releases glucose into blood)
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3
Q

where does glycogen metabolism occur?

A
  • cytosol
  • present in most cell types
  • glucose-6-phosphate only present in liver (required for glucose export)
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4
Q

what is the rate limiting enzyme of glycogen synthesis?

A

glycogen synthase

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5
Q

what is the rate limiting enzyme of glycogen breakdown?

A

glycogen phosphorylase

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6
Q

what is the feedback cycle of glycogen metabolism in a fed state? (3)

A
  • 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
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7
Q

what is the feedback cycle of glycogen metabolism in a fasting/exercise state?

A
  • increase glucagon/epinephrine→ activate phosphorylase, inhibit synthase
  • AMP/Ca2+→ activates glycogen phosphorylase→ increase glycogen breakdown
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8
Q

how is glycogen metabolism regulated in high energy need?

A

high energy state→ fall ATP→ increase AMP, increase Ca→ activate glycogen phosphorylase→ increase breakdown, decrease synthesis

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9
Q

how is glycogen metabolism regulated in low energy need?

A

low energy need→ high ATP, high G6P→ increase synthesis, decrease breakdown

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10
Q

what is the relation of DM to glycogen metabolism?

A

DM: insulin deficiency→unopposed glucagon action even in fed state→ activates glycogen breakdown→ increase glucose

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11
Q

what glycogen storage disease type affects glycogen synthesis?

A

only type 4 (andersen)

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12
Q

what are the glycogen storage disease types that affect glycogen breakdown?

A

types 1, 2, 3, 5

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13
Q

what is von gierke (type 1) glycogen storage disease? (enzyme + organ)

A
  • deficiency of glucose 6 phosphatase
  • G6P accumulates in liver/kidneys
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14
Q

what are the manifestations of von gierke (type 1) and cori (type 3) diseases?

A
  • fasting hypoglycemia
  • organomegaly
  • type1: lactate/uric acid accumulation
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15
Q

what is pompe disease (type 2)? (enzyme + organ)

A
  • deficiency of 1-4 glucosidase (debranching enzyme in LYSOSOMES)
  • esp affects heart→ cardiac failure/cardiomegaly
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16
Q

what is cori disease (type 3)? (enzyme + organ)

A
  • deficiency of debranching enzymes
  • in liver, heart, muscles
17
Q

what is andersen disease (type 4)?

A
  • deficiency of branching enzymes
  • affects liver!!→ hepatosplenomegaly, early death
18
Q

what is mcardle disease (type 5)?

A
  • deficiency of glycogen phosphorylase - in skeletal muscles
19
Q

what are the manifestations of mcardle disease (type 5)?

A

exercise induced muscle cramps/pain