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Fructose

Fructose. Muscle Fructose  Fructose-6-Phosphate Hexokinase Fructose-6-phosphate enters Glycolysis. Fructose. Liver Fructose  Fructose-1-Phosphate Fructokinase Fructose-1-phosphate  Dihydroxyacetonephosphate + Glyceraldehyde F1P aldolase Dihydroxyacetonephosphate enters glycolysis

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Fructose

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  1. Fructose • Muscle • Fructose  Fructose-6-Phosphate • Hexokinase • Fructose-6-phosphate enters Glycolysis

  2. Fructose • Liver • Fructose  Fructose-1-Phosphate • Fructokinase • Fructose-1-phosphate  Dihydroxyacetonephosphate + Glyceraldehyde • F1P aldolase • Dihydroxyacetonephosphate enters glycolysis • Glyceraldehyde + ATP  Glyceraldehyde-3-phosphate + ADP • Glyceraldehyde Kinase • Glyceraldehyde-3-phosphate enters glycolysis • **Glycerol-3-phosphate is an intermediate of this reaction. It is used to make phospholipids and triacylglycerols.

  3. Galactose • Galactose + ATP  Galactose-1-phosphate + ADP • Galactokinase • Galactose-1-phosphate + UDP-glucose  Glucose-1-phosphate + UDP-galactose • UDP-glucose is regenerated • UDP-galactose  UDP-glucose • UDP-galactose epimerase • Glucose-1-phosphate is mutated • Glucose-1-phosphate  Glucose-6-phosphate • Phosphoglucomutase • Glucose-6-phosphate enters glycolysis

  4. Mannose • Mannose + ATP  Mannose-6-phosphate + ADP • Hexokinase • Mannose-6-phosphate  Fructose-6-phosphate • Phosphomannose isomerase

  5. Pentose Phosphate Pathway • AKA: Hexose Monophosphate Shunt • Used to generate • NADPH for lipid synthesis • Ribose-5-phosphate for nucleotide synthesis

  6. Pentose Phosphate Pathway • Stage 1: • Oxidative reactions yield Ribulose-5-phosphate and NADPH • 3 Glucose-6-phosphate + 6 NADP+ + 3 H2O  6 NADPH + 6 H+ + 3 CO2 + 3 Ribulose-5- phosphate

  7. Pentose Phosphate Pathway • Stage 2: • Isomerization and epimerization reactions • 3 Ribulose-5-phosphate Ribose-5-phosphate + 2 Xylulose-5-phosphate

  8. Pentose Phosphate Pathway • Stage 3: • C-C bond cleavage and formation reactions • Ribose-5-phosphate + 2 Xylulose-5-phosphate 2 Fructose-6-phosphate + Glyceraldehyde-3-phosphate

  9. Glycogen Synthesis • Glucose-1-phosphate  Glycogen + Pi • (+) change in free energy (G) • Couple reaction with hydrolysis of UTP  overall (-) G • Activate Glucose to UDP-glucose • Glucose-1-phosphate + UTP + H2O  UDP-glucose + 2 Pi G is –33.5 • UDP-glucose + Glycogenn  Glycogenn+1 + UDP + 2 Pi • Glycogen synthase • Glycogen Branching Enzyme • Transfers 7 residues to another glycogen chain

  10. Glycogen Breakdown • Glycogenolysis • Glycogen phosphorylase causes release of Glucose-1-phosphate • Glycogen debranching enzyme • Phosphoglucomutase • Liver** • Glucose-6-phosphatase • Glucose-6-phosphate  Glucose + Pi

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