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Human Function- Exam 4 Material > Glycogen Synthesis/Pentose Shunt- Wimmer > Flashcards

Glycogen Synthesis/Pentose Shunt- Wimmer Flashcards

1
Q

what are the goals of the fed state?

A

lower blood glucose back to normal range
provide energy to tissues
convert excess calories to stored fuel (glycogen and fat)

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2
Q

what are the pathways of glucose usage? where does each occur?

A
  • glycolysis- all tissues
  • glycogen synthesis- liver and muscle
  • fatty acid + TAG synthesis- liver
  • pentose shunt- most tissues (especially liver during FA synthesis)
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3
Q

fates of glucose-6-phosphate during the fed state

A
  • glycogen
  • CO2 (aerobic)
  • lactate (anaerobic)
  • fatty acids/TAGs
  • nucleic acids
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4
Q

what converts glucose to glucose-6-P?

A

hexokinase

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5
Q

what is the intermediate of nucleic acid synthesis?

A

ribose-5-phosphate

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6
Q

what is the intermediate of glycogen synthesis?

A

glucose-1-phosphate

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7
Q

where is NADPH made?

A

pentose shunt

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8
Q

what uses NADPH?

A

fatty acid/TAG synthesis

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9
Q

what leaves regular glucose oxidation to form fatty acids?

A

acetyl-CoA

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10
Q

what converts pyruvate to acetyl CoA?

A

pyruvate dehydrogenase

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11
Q

what is the structure of glycogen?

A 
glucose polymer with alpha 1,4 and alpha 1,6 glycosidic bonds
highly branched (branches joined by alpha1,6 bonds
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12
Q

what is the purpose of the “non reducing” ends of glycogen?

A

lots of sites increases rate of synthesis and breakdown (ends are only location where glucoses can be added or removed)

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13
Q

where is glycogen stored? what is it used for?

A

liver- maintain blood glucose during fasting

muscle- uses for own energy needs

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14
Q

what enzyme converts glucose-6-phosphate to glucose-1-phosphate?

A

phosphoglucomutase

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15
Q

how is glycogen made?

A
  1. glucose-6-phosphate to glucose-1-phosphate
  2. glucose-1-phosphate is activated by addition of UDP from UTP (pyrophosphate released)
  3. glycogen synthase adds activated glucoses via alpha 1,4 bonds
  4. branching enzyme cleaves a section of the chain and relocates it to a branch site and adds via alpha 1,6 bond
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16
Q

what is the role of glycogen synthase?

A

add UDP glucoses to a chain with alpha 1,4 bonds

17
Q

what is the role of branching enzyme?

A

add branches of alpha 1,4 linked glucoses to a larger chain via alpha 1,6 linkage

18
Q

what is the energy requirement for glycogen synthesis?

A

2 phosphates per glucose added- energy is stored in the polymer and released when the polymer is broken down

19
Q

what is the reversible step in glycogen synthesis?

A

phosphogulcomutase changing glucose-6-phosphate to glucose-1-phosphate

20
Q

why does UDP on glucose make it activated?

A

good leaving group

21
Q

where does the UDP on glucose come from?

A

UTP

22
Q

what is released when glucose is added to a growing chain?

A

UDP

23
Q

what is the pentose shunt?

A

branch point of glucose oxidation that is used to make nucleic acids

24
Q

what are the two branches of the pentose shunt?

A

oxidative and nonoxidative branches

25
Q

what is the oxidative branch of the pentose shunt?

A

glucose oxidized to ribulose-5-phosphate (CO2 released)

makes NADPH for fatty acid/TAG synthesis

26
Q

where does the pentose shunt take place?

A

cytoplasm

27
Q

is the oxidative branch reversible or irreversible?

A

irreversible- maintain high NADPH/NADP+ ratio

28
Q

what is the rate limiting step of the oxidative branch? is it regulated?

A

glucose-6-phosphate dehydrogenase

regulated

29
Q

what does the non oxidative branch do?

A

provides ribose-5-phosphate for nucleic acid synthesis

30
Q

what happens during the non oxidative branch?

A

reversible interconversions of aldoses and ketoses via transaldolase and transketolase enzymes

31
Q

what happens to ribose-5-phosphate if it is not needed?

A

converted back to reenter glycolysis

32
Q

what regulates the pentose shunt?

A

cellular demand of NADPH

33
Q

what is NADPH used for?

A

biosynthesis (mainly FA/TAG synthesis)

34
Q

what hormone governs the fed state?

A

insulin

35
Q

what inhibits glucose-6-phosphate dehydrogenase?

A

NADPH

36
Q

when is glucose-6-phosphate dehydrogenase activated?

A

after a meal in the presence of insulin

37
Q

what happens in glucose-6-phosphate dehydrogenase deficiency?

A

not usually a problem, but certain things put oxidative stress on RBCs which spills reducing contents
NADPH is not present at high enough quantity–>hemolytic anemia (low hemotocrit and hemoglobin)

38
Q

what is NADPH used for in the RBCs?

A

maintaining a reducing atmostphere

Human Function- Exam 4 Material (25 decks)

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