Glycogen Synthesis/Pentose Shunt- Wimmer Flashcards
what are the goals of the fed state?
lower blood glucose back to normal range
provide energy to tissues
convert excess calories to stored fuel (glycogen and fat)
what are the pathways of glucose usage? where does each occur?
- glycolysis- all tissues
- glycogen synthesis- liver and muscle
- fatty acid + TAG synthesis- liver
- pentose shunt- most tissues (especially liver during FA synthesis)
fates of glucose-6-phosphate during the fed state
- glycogen
- CO2 (aerobic)
- lactate (anaerobic)
- fatty acids/TAGs
- nucleic acids
what converts glucose to glucose-6-P?
hexokinase
what is the intermediate of nucleic acid synthesis?
ribose-5-phosphate
what is the intermediate of glycogen synthesis?
glucose-1-phosphate
where is NADPH made?
pentose shunt
what uses NADPH?
fatty acid/TAG synthesis
what leaves regular glucose oxidation to form fatty acids?
acetyl-CoA
what converts pyruvate to acetyl CoA?
pyruvate dehydrogenase
what is the structure of glycogen?
glucose polymer with alpha 1,4 and alpha 1,6 glycosidic bonds highly branched (branches joined by alpha1,6 bonds
what is the purpose of the “non reducing” ends of glycogen?
lots of sites increases rate of synthesis and breakdown (ends are only location where glucoses can be added or removed)
where is glycogen stored? what is it used for?
liver- maintain blood glucose during fasting
muscle- uses for own energy needs
what enzyme converts glucose-6-phosphate to glucose-1-phosphate?
phosphoglucomutase
how is glycogen made?
- glucose-6-phosphate to glucose-1-phosphate
- glucose-1-phosphate is activated by addition of UDP from UTP (pyrophosphate released)
- glycogen synthase adds activated glucoses via alpha 1,4 bonds
- branching enzyme cleaves a section of the chain and relocates it to a branch site and adds via alpha 1,6 bond
what is the role of glycogen synthase?
add UDP glucoses to a chain with alpha 1,4 bonds
what is the role of branching enzyme?
add branches of alpha 1,4 linked glucoses to a larger chain via alpha 1,6 linkage
what is the energy requirement for glycogen synthesis?
2 phosphates per glucose added- energy is stored in the polymer and released when the polymer is broken down
what is the reversible step in glycogen synthesis?
phosphogulcomutase changing glucose-6-phosphate to glucose-1-phosphate
why does UDP on glucose make it activated?
good leaving group
where does the UDP on glucose come from?
UTP
what is released when glucose is added to a growing chain?
UDP
what is the pentose shunt?
branch point of glucose oxidation that is used to make nucleic acids
what are the two branches of the pentose shunt?
oxidative and nonoxidative branches
what is the oxidative branch of the pentose shunt?
glucose oxidized to ribulose-5-phosphate (CO2 released)
makes NADPH for fatty acid/TAG synthesis
where does the pentose shunt take place?
cytoplasm
is the oxidative branch reversible or irreversible?
irreversible- maintain high NADPH/NADP+ ratio
what is the rate limiting step of the oxidative branch? is it regulated?
glucose-6-phosphate dehydrogenase
regulated
what does the non oxidative branch do?
provides ribose-5-phosphate for nucleic acid synthesis
what happens during the non oxidative branch?
reversible interconversions of aldoses and ketoses via transaldolase and transketolase enzymes
what happens to ribose-5-phosphate if it is not needed?
converted back to reenter glycolysis
what regulates the pentose shunt?
cellular demand of NADPH
what is NADPH used for?
biosynthesis (mainly FA/TAG synthesis)
what hormone governs the fed state?
insulin
what inhibits glucose-6-phosphate dehydrogenase?
NADPH
when is glucose-6-phosphate dehydrogenase activated?
after a meal in the presence of insulin
what happens in glucose-6-phosphate dehydrogenase deficiency?
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)
what is NADPH used for in the RBCs?
maintaining a reducing atmostphere
