1 / 51

Energy Harvesting Pathways

Energy Harvesting Pathways. Photosynthesis. photosynthesis. reverses the oxidation of glycolysis/respiration C 6 H 12 O 6 +6 O 2 => 6 CO 2 +6 H 2 O + energy energy +6 CO 2 +12 H 2 O =>6 O 2 +C 6 H 12 O 6 +6 H 2 O. photosynthesis. reverses the oxidation of glycolysis/respiration

molimo
Download Presentation

Energy Harvesting Pathways

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. Energy Harvesting Pathways Photosynthesis

  2. photosynthesis • reverses the oxidation of glycolysis/respiration C6H12O6 +6 O2 => 6 CO2 +6 H2O + energy energy +6 CO2 +12 H2O =>6 O2 +C6H12O6 +6 H2O

  3. photosynthesis • reverses the oxidation of glycolysis/respiration • reduces highly oxidized carbon • stores energy in hydrocarbon bonds • utilizes “free” resources • water from soil reservoir • CO2 from atmospheric reservoir • energy from diurnal light source • releases O2 as a byproduct

  4. reactants and products of photosynthesisFigure 8.1

  5. photosynthesis • occurs in chloroplasts • “light reactions” on thylakoid membranes • “dark reactions” in aqueous stroma • two interconnected pathways • light-driven electron transport generates reductant & energy • Calvin-Benson cycle reduces CO2 & assembles carbohydrates

  6. photosynthesis: overviewFigure 8.3

  7. visible light occupies a narrow band of the electromagnetic spectrumFigure 8.5

  8. photosynthetic light reactions • light is the visible portion of the electromagnetic radiation spectrum • between ultraviolet and infrared • light travels in wave-like fashion • wavelength & frequency are inversely related • shorter wavelength : higher frequency • longer wavelength : lower frequency

  9. photosynthetic light reactions • light energy occurs in discrete units: photons • energy of a photon is inversely proportional to wavelength • shorter wavelength : higher energy • longer wavelength : lower energy • intensity measures number of photons striking a unit area per unit time (e.g. µE·m-2·s-1)

  10. green light istransmitted (and reflected) as blue and red are absorbed

  11. photosynthetic light reactions • molecules absorb electromagnetic radiation • pigments absorb visible light of certain wavelengths • photon-pigment interactions • reflection • transmission • absorption - pigment is excited by photon • excited state - ground state = energy of photon

  12. absorption of a photon excites a moleculeFigure 8.4

  13. absorption and action spectraFigure 8.6

  14. Chlorophyll a:√ tetrapyrrole ring √ coordinated Mg√ hydrophobic tail Figure 8.7

  15. photosynthetic light reactions • molecules absorb electromagnetic radiation • a pigment absorbs only certain wavelengths • an absorption spectrum is a molecular fingerprint • an action spectrum plots effectiveness vs. wavelength • eukaryotic photosynthesis uses chlorophyll a as the central pigment • accessory pigments transfer energy to Chl a • in plants: Chl b, carotenoids

  16. photosynthetic electron transport mutants fluoresce…

  17. photosynthetic light reactions • possible fates of absorbed energy • loss as heat • loss as fluorescence • intermolecular transfer • direct transfer • electron transport

  18. fates of energyFigure 8.8

  19. photosynthetic light reactions • excited reaction center chlorophyll a is a good reducing agent • PSII Chl a* drives electron transport through carriers in the thylakoid membrane • PSI reaction center chlorophyll is reduced by electrons transported from PSII • PSI Chl a reduces NADP+ => NADPH • PSII Chl a+is reduced with e- from H2O • O2 is released as a byproduct

  20. Figure 8.9

  21. thylakoids are flat sacks that reside in the chloroplastFigure 8.11

  22. transfers of absorbed energyFigure 8.11

  23. photosynthetic light reactions • noncyclic electron transport produces ATP and NADPH • cyclic electron transport produces ATP, but not NADPH

  24. Cyclic electron transportFigure 8.10

  25. the light reactions of photosynthesisFigure 8.11

  26. the light reactions of photosynthesis • electrons flow from water to NADP+ • NADPH is produced • a proton gradient is formed • ATP is produced

  27. light and “dark” reactions are coupled by ATP & NADPHFigure 8.3

  28. carbon fixation reactions • How does the plant incorporate CO2 into the existing “carbon pool”? • CO2 must be attached to one or more existing molecules - which one(s)? • …feed a plant CO2 and watch where it goes…

  29. Calvin, Benson, et al.photosynthesis in Chlorellawith 14CO2Figure 8.12

  30. carbon fixation reactions • 3-phosphoglycerate is the first product of carbon fixation • other molecules were labeled over time

  31. Calvin-Benson Cycle model of carbon fixationFigure 8.13 12 3PG

  32. carbon fixation reactions • the acceptor is not a 2-carbon molecule • it’s ribulose 1,5-bisphosphate • a 5-C sugar • the first product is not 3PG • it’s an unstable 6-C intermediate

  33. 3PG is the first stable productFigure 8.14

  34. Calvin-Benson Cycle model of carbon fixationFigure 8.13

  35. Calvin-Benson Cycle model of carbon fixationFigure 8.13

  36. carbon fixation reactions • Calvin-Benson cycle accomplishes three tasks • carbon fixation - by rubisco • reduction of fixed C into carbohydrate • 3-phosphoglyceric acid => • glyceraldehyde 3-phosphate • requires reductant & energy • formation of more RuBP (hence, cycle) • requires multiple enzymes & ATP

  37. Calvin-Benson Cycle model of carbon fixationFigure 8.13

  38. Product of Calvin-Benson Cycle • G3P is the reduced product of the Calvin-Benson cycle

  39. Product of Calvin-Benson Cycle • G3P is the reduced product of the Calvin-Benson cycle

  40. Product of Calvin-Benson Cycle • G3P is the reduced product of the Calvin-Benson cycle • 1/6 of G3P is product; 5/6 are reaction intermediates • “excess” G3P is used to make monosaccharides • 1/3 of G3P is stored in the chloroplast as starch • 2/3 of G3P is transported elsewhere as sucrose

  41. Figure 8.3

  42. carbon fixation reactions • ribulose bisphosphate carboxylase/oxygenase • Rubisco • most abundant protein in the world, but…

  43. photorespiration • ribulose bisphosphate carboxylase/oxygenase is very ineffective • rubisco adds CO2 to RuBP or adds O2 to RuBP • 5C + 1C => 2 · 3C • 5C + 0C => 2C + 3C • costs ATPs to regenerate RuBP

  44. chloroplast, peroxisome, mitochondrionFigure 8.15

  45. photorespiration • ribulose bisphosphate carboxylase/oxygenase • carboxylase & oxygenase activities compete • rubisco CO2 affinity is low • stomata must be open for efficient PS • easy access for 20% O2 & 0.035% CO2 • up to 30% of fixed carbon is lost to photorespiration in important crops plants • some plants don’t suffer so much from photorespiration

  46. photorespiration - solution • C3 plants and C4 plants • 3PG is the first detectable product of C fixation in C3 plants • C4 plants produce a 4-C product first PEP + CO2 ======> oxaloacetate 3C 1C PEP C’ase 4C • PEP carboxylase • has high CO2 affinity • is never an oxygenase

  47. photorespiration - solution • but… • C4 plants use rubisco, just like C3 plants • PEP carboxylase and rubisco are separated into different compartments

  48. C3 & C4 leaf anatomiesFigure 8.16

  49. mesophyll cells and bundle sheath cells communicate in C4 plantsFigure 8.17

  50. photorespiration - solution • C4 bundle sheath cells are enriched in CO2 relative to O2 • rubisco fixes O much less often spatial separation of initial C fixation and Calvin Benson cycle

More Related