Term
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Definition
- if the amount of glucose stored in the cell was dissolved freely then it would change the osmotic properties of the cell---.4M
- storing glucose as a poylmer instead reduces the concentation to .01uM
- glycogen in muscle provides a source of quick energy and glycogen is exhausetd in less than an hour during activity
- liver glycogen is reservoir for tissues like the brain, which can't use fatty acids as fuel- depleted in 12-25hr
- fat stores more energy than glycogen but can't be converted to glucose
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Term
| Glycogen Breakdown is Catalyzed by Glycogen Phosphorylase |
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Definition
- In muscle an liver, glycogen suplies glycolytic pathway with glucose through the action of three enzymes
- glycogen phosphorylase catalyzes the reaction in which alpha 1-4 glycosidic bonds between 2 glucose residues at non reducing ends are attacked by Pi, removing a terminal glucose as Glucose 1-phosphate
- [image]
- in the phosphorylysis reaction some energy of the glycosidic bond is preserved in forming a phosphate bond
- pyridoxal phosphate is an essential cofactor here. its phosphate group acts as a a general acid catalyst, promoting attack by Pi on the glycosidic bond
- glycogen phosphorylase acts until its gets four residues away from an alpha 1-6 branch point
- at this point a debranching enzyme catalyzes two reactions that transfer branches
- [image]
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Term
| Glucose 1-Phosphate Enters Glyolysis or, in liver, replenishes Blood Glucose |
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Definition
- glucose 1-phosphate interconversion to Glucose 6-Phosphate by phosphoglucomutase
- [image]
- 1)enzyme is phosphorylated on a ser residue
- 2)enzyme donates its phosphoryl group to glucose 1-phosphate...=glucose 1,6 bisphosphate
- 3)phosphoryl group at C-1 of glucose 16 BP is transferred back to the enzyme
- G6P formed in skeletal muscle can enter glycolysis and serve as an energy source
- in liver, glycogen breakdown releases glucose into the blood when glucose lvl drops. requires glucose 6 phosphatase and various glucose transporters. muscle doesnt have this enzyme and therefore cannot convert G6P to glucose and get it into teh blood
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Term
| Sugar Nucleotide UDP-Glucose Donates Glucose for Glycogen Synthesis |
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Definition
- many reactions in which hexoses are transformed involve sugar nucleotides
- these are compounds in which anomeric carbon of sugar is activated by attachment to a nucleotide thru phosphate ester linkage
- used as substrated for polymerization into many types of saccharides (mono, di, poly, starch, cellulose etc)
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Term
| Properties of Sugar Nucleotides which Make them Good for Biosynthesis |
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Definition
- their formation is irreversible, making their pathways irreversible. The free energy of the reactions is always large and negative, the products are removed quickly and synthetic reactions are pushed
- the nucleotide moiety of sugar nucleotides can undergo many noncovalent interactions with enzymes, allowing for additional free energy of binding to contribute to reaction favorability
- the nucleotide group(UMP, ATP) is a good leaving group, facilitating nucleophilic attack by activating sugar carbon to which it is attached
- cells can sequester hexoses with nucleotide groups on them from each other based on the group and fate of the molecule
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Term
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Definition
- Glycogen synthesis happens in almost all animal tissues, but mostly in liver and skeletal muscles
- starting point of glycoge synthesis is G6P
- catalyzed by hexokinaseI and II in muscle and IV in liver: D-Glucose+ATP-> D-Glucose 6-Phosphate+ADP
- some glucose is first taken up by erythrocytes and converted to lactate via glycolysis
- lactate then goes to liver and is converted to G6P by gluconeogenesis
- to initiate glycogen synthesis, G6P is converted to G1P using phosphoglucomutase
- G1P + UTP ->UDP-glucose + PPi
- [image]
- UDP glucose - donor of glucose residues in the reaction catalyzed by glycogen synthase.. promotes transfer of glucose residue from UDP glucose to nonreducing end of branched glycogen molecule
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