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S 2007 BIOC 3406

S 2007 BIOC 3406. 01-30-07. Glycolysis - Reactions. Hexokinase Isozyme in liver glucokinase Regulatory enzyme Phosphohexose isomerase Involves ring-opening and enediol intermediate PFK-1 Regulatory enzyme Fructose 2,6-bisphosphate potent allosteric activator

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S 2007 BIOC 3406

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  1. S 2007 BIOC 3406 01-30-07

  2. Glycolysis - Reactions • Hexokinase • Isozyme in liver glucokinase • Regulatory enzyme • Phosphohexose isomerase • Involves ring-opening and enediol intermediate • PFK-1 • Regulatory enzyme • Fructose 2,6-bisphosphate potent allosteric activator • Plants, bacteria can use PPi instead of ATP

  3. Glycolysis - Reactions • Aldolase • Animals and Plants use a Schiff base intermediate • Fungi, bacteria use a Zn2+ • TPI • Similar to phosphohexose isomerase reaction • Glyceraldehyde 3-phosphate dehydrogenase

  4. Rule of thumb: No more than 3 electron pairs mobilized in one step

  5. Glycolysis - Reactions • Phosphoglycerate kinase • First ATP generated • Phosphoglycerate mutase • 2 steps with 2,3-BPG intermediate (major component of erythrocytes) • Enolase • Pyruvate kinase

  6. Dehydration of 2-phosphoglycerate to Phosphoenolpyruvate G′° 7.5 kJ/mol

  7. Regulation of Glycolysis • ATP kept constant • Anaerobically (2molecules of ATP formed per glucose) much more glucose consumed per unit time than • Aerobically (~30 molecules of ATP formed per glucose) • Short term (time scale 1 sec) factors: • Allosteric reg of hexokinase, PFK-1, PK • Longer term larger scale • Glucagon, epinephrine, insulin, amounts of glycolytic enzymes

  8. Other carbs and glycolysis • Carb stores: Glycogen and Starch • Dietary carbs: glycogen, starch, disaccharides, monosaccharides

  9. Hydrolysis of carbs in gut: Disaccharides MUST be hydrolyzed to monosaccharides before entering cells • Dextrin + nH2O  n glucose • Maltose + H2O  2 glucose • Lactose + H2O  glucose + galactose • Sucrose + H2O  glucose + fructose • Trehalose + H2O  2 glucose

  10. NADH + H+ NAD+ Mistake in your book

  11. Anaerobic fates of pyruvate • Tied to fate of NADH formed in glycolysis • O2 should be acceptor of NADH’s reducing equivalent, but if it is not… • Pyruvate is fermented and NADH  NAD+ + H+ • Lactic acid fermentation • Ethanol fermentation

  12. This is resonance but is shown incorrectly. The two forms do not have different structures

  13. Gluconeogenesis • Not just the reverse of glycolysis • Must substitute for regulatory steps • Avoid futile cycling

  14. Pyruvate + ATP + GTP + HCO3-→ PEP + ADP + GDP + Pi + CO2

  15. Note how much it costs to convert pyruvate to glucose!

  16. Next • Details of Gluconeogenesis • Pentose Phosphate Pathway

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