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Chapter 27

Chapter 27. Specific Catabolic Pathways:. Carbohydrate, Lipid & Protein Metabolism. 1. 2. 3. Glycolysis : Follow Along: Figure 27.3. Glycolysis. 10 enzyme-catalyzed reactions by which glucose is oxidized to two molecules of pyruvate.

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Chapter 27

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  1. Chapter 27 Specific Catabolic Pathways: Carbohydrate, Lipid & Protein Metabolism

  2. 1. 2. 3.

  3. Glycolysis: Follow Along: Figure 27.3

  4. Glycolysis • 10 enzyme-catalyzed reactions by which glucose is oxidized to two molecules of pyruvate. • During glycolysis, there is net conversion of 2ADP to 2ATP. NOTE: ATP = Energy molecule of choice

  5. Glycolysis - Rxn 1 • reaction 1:phosphorylation of -D-glucose.

  6. Glycolysis - Rxn 2 • reaction 2:isomerization of glucose 6-phosphate to fructose 6-phosphate.

  7. Glycolysis - Rxn 2 • This isomerization is most easily seen by considering the open-chain forms of each monosaccharide; it is one keto-enol tautomerism followed by another.

  8. Glycolysis - Rxn 3 • reaction 3: phosphorylation of fructose 6-phosphate. ATP ADP

  9. Glycolysis - Rxn 4 • reaction 4:cleavage of fructose 1,6-bisphosphate to two triose phosphates.

  10. Glycolysis - Rxn 5 • reaction 5: isomerization of triose phosphates. • Catalyzed by phosphotriose isomerase. • Reaction involves two successive keto-enol tautomerizations. • Only the D enantiomer of glyceraldehyde 3-phosphate is formed.

  11. Glycolysis - Rxn 6 • Reaction 6: oxidation of the -CHO group of D-glyceraldehyde 3-phosphate. • The product contains a phosphate ester and a high-energy mixed carboxylic-phosphoric anhydride.

  12. Glycolysis - Rxn 7 • Reaction 7: transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP.

  13. Glycolysis - Rxn 8 & 9 • Reaction 8: isomerization of 3-phosphoglycerate to 2-phosphoglycerate. • Reaction 9: dehydration of 2-phosphoglycerate.

  14. Glycolysis - Rxn 10 • Reaction 10: phosphate transfer to ADP

  15. Glycolysis: SUMMARY: 1 ATP used 1 ATP used Figure 27.3 2 ATP produced Note: Glycer-3 phosphate X 2 2 ATP produced

  16. Glycolysis: Summary • The net equation for glycolysis:

  17. Confirming your knowledge • Of the 36 molecules of ATP produced by the complete metabolism of glucose, how many are produced in glycolysis alone? ____ • What is the net total ATP production? ___ ATP Total: 36 ATP

  18. Reactions of Pyruvate: Fig 27.4 • Pyruvate metabolized three ways: • depends on organism & presence/absence of O2 NOTE: Anaerobic = w/o Oxygen Aerobic = w/ Oxygen

  19. Reactions of Pyruvate • A key to understanding the biochemical logic behind two of these reactions of pyruvate is to recognize that glycolysis needs a continuing supply of NAD+. • If no oxygen is present to reoxidize NADH to NAD+, then another way must be found to reoxidize it.

  20. Pyruvate to Lactate • Under anaerobic (NO Oxygen) conditions, the most important pathway for the regeneration of NAD+ is reduction of pyruvate to lactate. Pyruvate, the oxidizing agent, is reduced to lactate.

  21. Pyruvate to Lactate • While reduction to lactate allows glycolysis to continue, it increases the concentration of lactate and also of H+ in muscle tissue • When blood lactate reaches about 0.4 mg/100 mL, muscle tissue becomes almost completely exhausted, esp. b/c H+ ions. ((ACID!))

  22. Pyruvate to Ethanol • Yeasts and several other organisms regenerate NAD+ by this two-step pathway: • decarboxylation of pyruvate to acetaldehyde. • Acetaldehyde is reduced to ethanol.

  23. Pyruvate to Acetyl-CoA • Under aerobic conditions, pyruvate undergoes oxidative decarboxylation. • The carboxylate group is converted to CO2. • The remaining two carbons are converted to the acetyl group of acetyl CoA.

  24. Confirming your knowledge • The end product of glycolysis (pyruvate) cannot enter as such into the citric acid cycle. • What is the name of the process that converts this C3 compound to a C2 compound?

  25. Catabolism of Glycerol • Glycerol enters glycolysis via dihydroxyacetone phosphate. 7.3 kcal/mole 3.4 kcal/mole.

  26. Challenge Question • Which yields more Energy upon hydrolysis: ATP or glycerol 1- phosphate and Why?

  27. Summary • Glycolysis yields 2 net ATP • ATP is the molecule of choice for cell(s) Energy • ATP is a High E yielding molecule (7.3 kcal/mole) • Pyruvate is the END product of Glycolysis • under aerobic conditions  Acetyl CoA  further ATP!!! • under anaerobic conditions  Lactate  (muscle fatigue)

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