Scribe.Lecture 15.docx

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University of Toronto St. George
Cell and Systems Biology
William Navarre

Lecture 15: Phototrophs Summary of last class 3 chemoorganotrophic 1. organic compounds are a source of NRG & carbon for biosynthesis 2. aerobic respiration 1. flow of electrons from organic compounds to oxygen 2. down ETC 3. mvmt of electrons by proton gradient across CM 3. organic electron acceptors 1. electron flow from one compound to another 4. we will learn about electron flow to other molecules apart from oxygen 4 phototropic electron acceptors 5. flow of electrons through a photosystem that harnesses the NRG to drive a PMT that can be used by ATP synthase to generate ATP 6. some bacteria can use light to generate NRG 7. photoheterotrophs use organic compounds as building blocks for the molecules 8. photoautotrophs use CO 2 9. they’ll fix that to generate sugars 5 phototrophy 10. phototrophy is widespread in the prokaryotic world 11. photosynthesis is defined as… 12. there are 2 possible phototrophs 6 why study… 13. bacteria are a great model for studying many things 14. can do rapid genetics on them 15. great way to understand our planet’s history – how the atmosphere changed over time, contribution of microbes to oxygen 16. use to infer if there is life on other planets 17. harness microbial photosynthesis to make biofuels – to produce a lot of sugars 18. treat polluted water, bacteria that require 2 S for photosynthesis will remove it from the envmt 19. generate sources of N to plants (fertilizer) w the use of little NRG 7 timeline of photosynthesis on earth 20. 3-4 bya there were the first photosynthetic bacteria 1. precede plants by a lot 2. produced sulfer or sulfate compounds rather than O – c2anging the geology 21. 2.4-2.3 bya first evidence of atmospheric O 2 22. and around that time, were the first signs of cyanobacteria 1. first bacteria to produce O2 23. microbes dominanted the world early and discovered photosynthesis to get as much NRG wheever they want 8 24. groups are trying to harness this capactiry of photosynthetic microbes to generate biofuels 25. ex. Proterro 26. use photosynthetic bacteria to generate sugar that can be fermented to ethanol 27. hopefully key way to harness light NRG 28. a third of the cost of growing crops 9 photosystems 29. photosystmes are the machines that drive photosynthesis 30. they get NRG form ET 31. act like ETC 1. they generate PMT across photosynthetic membrane 10 ETC 32. for chemoorganotrophs, they generate the reductant NADH 33. start off at top of ETC tower 34. pass electrons & protons to NADH dehydrogenase (Complex I) 35. electrons will go through to the quinone pool and 2 protons will go out 36. quinone pool will pass electrons through across CM 37. electrons will go through Complex II, IV, then generate water 38. these proton pumping steps across the CM gives the electrochemical potential 39. this can be used for protein synthesis 11 40. photosystem is simalr 41. there is an electron tower w diff reductants & diff reductant potentials and it is cyclic 42. light hits a reaction centre 43. reductant is generated which will pass electrons down the ET tower 44. into the quinone pool in the 2 complex and electrons go through round and round in a cycle – cyclic photophorphorylation 45. as electrons mv through the quinon pool, protons go out of the photosynthetic membrane and a proton gradient drives ATP synthesis 12 photosystems 46. these photosystems are present in photosynthetic membranes 47. can be in bacteria in may places 1. CM 2. chorosomes 3. thylakoids 13 chloroplasts 48. stacked thylakoids concentrate photosynthetic power 14 purple bacteria 49. purple bacteria have photosynthetic vesicles 15… 50. photosynthetic membranes increase the surface area 16 51. chlorosomes are the photosynthetic strubutres 17 52. chlorosomes are immersed in bacterial chlorophyll 18 53. 19 54. chlorophyll a is a proyphrin ring w Mg at centre and side chains of… 55. these modifications lead to an absorption spectra 20 56. bacteriochlorphyll have modifications at these sites and these lead to absorption spectra of … 21 57. if you modify a site of side chains 58. potential modifications 59. diff wavelengths of light absorved 60. gives bacteria to absorb lig
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