glycogen metabolism

Question 1

what is glycogen?

Answer 1

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

Question 2

what is the function of glycogen?

Answer 2

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

Question 3

where does glycogen metabolism occur?

Answer 3

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

Question 4

what is the rate limiting enzyme of glycogen synthesis?

Answer 4

glycogen synthase

Question 5

what is the rate limiting enzyme of glycogen breakdown?

Answer 5

glycogen phosphorylase

Question 6

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

Answer 6

• 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

Question 7

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

Answer 7

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

Question 8

how is glycogen metabolism regulated in high energy need?

Answer 8

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

Question 9

how is glycogen metabolism regulated in low energy need?

Answer 9

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

Question 10

what is the relation of DM to glycogen metabolism?

Answer 10

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

Question 11

what glycogen storage disease type affects glycogen synthesis?

Answer 11

only type 4 (andersen)

Question 12

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

Answer 12

types 1, 2, 3, 5

Question 13

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

Answer 13

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

Question 14

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

Answer 14

• fasting hypoglycemia
• organomegaly
• type1: lactate/uric acid accumulation

Question 15

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

Answer 15

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

Question 16

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

Answer 16

• deficiency of debranching enzymes
• in liver, heart, muscles

Question 17

what is andersen disease (type 4)?

Answer 17

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

Question 18

what is mcardle disease (type 5)?

Answer 18

• deficiency of glycogen phosphorylase - in skeletal muscles

Question 19

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

Answer 19

exercise induced muscle cramps/pain