1 / 73

ATP is the cell’s “energy” BUT Cells also have….REDUCING POWER! Processes (such as photosynthesis) require NADPH as well

Pentose Phosphate Pathway. Hexose monophosphate (HMP) shunt / Phosphogluconate pathway. ATP is the cell’s “energy” BUT Cells also have….REDUCING POWER! Processes (such as photosynthesis) require NADPH as well as ATP NADH and NADPH are NOT interchangable.

morwenna
Download Presentation

ATP is the cell’s “energy” BUT Cells also have….REDUCING POWER! Processes (such as photosynthesis) require NADPH as well

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Pentose Phosphate Pathway Hexose monophosphate (HMP) shunt / Phosphogluconate pathway. • ATP is the cell’s “energy” BUT • Cells also have….REDUCING POWER! • Processes (such as photosynthesis) require NADPH as well as ATP • NADH and NADPH are NOT interchangable

  2. NADH and NADPH are NOT interchangable • NAD+ participates in synthesis of ATP • glycoloysis, oxidative phosphorylation • NADPH is a reducing agent • produced in light reactions and consumed in Calvin cycle of photosynthesis NADP+ + 2H ---> NADPH + H+ In the cell… [NAD+] ~ 1000 [NADP+] ~ 0.01 [NADH] [NADPH]

  3. 3C1 3C6 3C5 2C5 to 1C7 + 1C3 1C5 to 1C5 2C5 to 2C5 1C7 + 1C3 to 1C6 + 1C4 1C4 + 1C5 to 1C6 + 1C3

  4. 3C6 ---> 3C5 + 3C1 2 3 2 Summary of carbon skeleton rearrangements in the pentose phosphate pathway.

  5. 3 ribulose-5-P ---> 2 xylulose-5-P + 1 ribose-5-P

  6. Transketolase: catalyzes the transfer of C2 units

  7. CH3 C7 C3

  8. Transaldolase: catalyzes the transfer of C3 units

  9. C7 C4 C3 C6

  10. C4 C5 C6 C3

  11. Summary of the pentose phosphate pathway 3G6P + 6NADP+ + 3H2O 6NADPH + 6H+ + 3CO2 + 2F6P + GAP Important intermediates Ribose-5-phosphate (nucleic acids, histidine) Erythrose-4-phosphate (aromatic amino acids)

  12. What is the purpose of the pentose phosphate pathway? Biosynthetic precursors NADPH for biosynthesis NADPH to keep cell reduced

  13. Oxygen Biochemistry Eº (V) vs. NHE +0.28 +1.35 +0.82 O2 + 2e- + 2H+ ----> H2O2 H2O2 + 2e- + 2H+ ----> 2H2O O2 + 4H+ + 4e- ----> 2H2O Reduction of O2 or H2O2 can be used as a thermodynamic driving force to drive oxidation of various molecules

  14. Oxidative Damage O2 + 2e- + 2H+ ----> H2O2 S ----> S2+ + 2e- H2O2 + 2e- + 2H+ ----> 2H2O S ----> S2+ + 2e- O2 + 4e- + 2H+ ----> 2H2O 2S ----> 2S2+ + 4e-

  15. Peptide and phosphodiester cleavage Iron-sulfur cluster disassembly

  16. Oxygen Diradical 2px* O O 2px 2px 2px 2py 2pz 2px 2py 2pz 2px 2px 2px 2s* 2s 2s 2s 1s* 1s 1s 1s

  17. 3O2(up/up) + 1X (paired) ---> 1XO2(paired) 1O2(paired) + 1X (paired) ---> 1XO2(paired) 3O2(up/up) + 3X (up/up) ---> 1XO2(paired) Need to alleviate spin restriction

  18. Eº (V) vs. NHE -0.33 +0.89 +0.38 +2.31 +0.28 +1.35 +0.82 ••O2 + e- ----> •O2- •O2- + e- + 2H+ ----> H2O2 H2O2 + e- + H+ ----> H2O + •OH •OH + e- + H+ ----> H2O ••O2 + 2e- + 2H+ ----> H2O2 H2O2 + 2e- + 2H+ ----> 2H2O ••O2 + 4H+ + 4e- ----> 2H2O

  19. Homolytic peroxide cleavage

  20. Heterolytic peroxide cleavage: The Fenton Reaction Catalyzed by metals like iron and copper Eº = +0.38 V

  21. •OH + RH ----> H2O + R• R• + ••O2 ----> ROO• RH + ROO• ----> R• + ROOH

  22. Antioxidants

  23. Free Radical Chain Reactions Initiation X2 ----> 2X• X• + RH ----> XH + R• Propagation R• + ••O2 ----> ROO• ROO• + RH ----> ROOH + R• Termination R• + ROO• ----> ROOR R• + R• ----> R2 ROO• + ROO• ----> ROOOOR ----> O2 + ROOR X = •OH, •O2-, ••O2

  24. If R = lipid The E/C couple Termination R• + EH ----> RH + E• ROO• + EH ----> ROOH + E• Recovery AH- + E• ----> A•- + EH A•- + E• ----> A + EH A + NADPH ----> AH- + NADP+ 1/6Glucose + NADP+ ----> 1/3CO2 + NADPH DHAR PPP or Photosynthesis DHAR = dehydroascorbate reductase PPP = pentose phosphate pathway

  25. If R = soluble, C or GSH Termination R• + AH- ----> RH + A•- ROO• + AH- ----> ROOH + A•- 2A•- + H+ ----> AH- + A Recovery A + NADPH ----> AH- + NADP+ 1/6Glucose + NADP+ ----> 1/3CO2 + NADPH Termination R• + GSH ----> RH + GS• ROO• + GSH ----> ROOH + GS• 2GS• ----> GSSG Recovery GSSG + NADPH + H+ ----> 2GSH + NADP+ 1/6Glucose + NADP+ ----> 1/3CO2 + NADPH

  26. Peroxide reduction Can be used to extract hydrides from substrates Eº = +1.35 V

  27. Oxygen reduction Can be used to extract hydrides from substrates Eº = +0.82 V

  28. Some Bacteria/Plants Acetyl-CoA CO2 fixation Fungi/plants

  29. Extant ways of fixing CO2 Reductive TCA cycle Calvin Cycle Acetyl-CoA Synthase

  30. Reversing the TCA Cycle Pyruvate ∆G <<< 0 ∆G <<< 0 ∆G ~ 0 ∆G ~ 0 ∆G ~ 0 ∆G ~ 0 ∆G <<< 0 ∆G ~ 0 ∆G ~ 0 ∆G <<< 0

  31. How do you reverse KGDH? Ketoglutarate synthase 2-oxoglutarate:ferredoxin oxidoreductase Photosynthetic bacteria Anaerobic bacteria

  32. What about isocitrate dehydrogenase? This step can be made reversible if you use a different source of electrons. Use NADPH instead of NADH.

  33. Citrate lyase

  34. Pyruvate synthase Acetyl-CoA + CO2 ---> pyruvate Pyruvate:ferredoxin oxidoreductase Photosynthetic bacteria Anaerobic bacteria

  35. Other bacteria Furdui, C. et al. J. Biol. Chem. 2000;275:28494-28499

  36. The Calvin cycle. 3CO2 -----> GAP 9 ATP and 6 NADPH

  37. 6C3 6C3 3C5 3C1 1C3 C4 C3+C3 C3+C4 C6 C7 C5 C5 C6+C3 C7+C3

  38. Most important enzyme is Ribulose-5-phosphate carboxylase (Rubisco)

  39. Transketolase: catalyzes the transfer of C2 units Aldolase: catalyzes the condensation of C3 ketoses with aldoses

  40. C3 + C3 ---> C6 C3 + C6 ---> C4 + C5 C3 + C4 ---> C7 C3 + C7 ---> C5 + C5 Overal reaction = 5C3 ---> 3C5 3CO2 + 9ATP + 6NADPH ---> GAP + 9ADP + 8Pi + 6NADP+ 1 GAP molecule is made from 3CO2 GAP is converted to glucose by gluconeogenesis

  41. Aldolase C3 + C3 = C6 Reverse of the step in glycolysis

  42. Transketolase C3 + C6 = C4 + C5

More Related