2. Light-independent (dark) reactions occur in the stroma of the chloroplast (pH 8) Consumes ATP & NADPH from light reactions regenerates ADP, Pi and NADP +

3. fixing CO 2 1) RuBP binds CO 2

4. fixing CO 2 1)RuBP binds CO 2 2) rapidly splits into two 3-Phosphoglycerate therefore called C3 photosynthesis

5. Reversing glycolysis G3P has 2 possible fates 1) 1 in 6 becomes (CH 2 O) n 2) 5 in 6 regenerate RuBP

6. Reversing glycolysis 1 in 6 G3P becomes (CH 2 O) n either becomes starch in chloroplast (to store in cell) or is converted to DHAP & exported to cytoplasm to make sucrose Pi/triosePO 4 antiporter only trades DHAP for Pi

7. Regenerating RuBP Basic problem: converting a 3C to a 5C compound must assemble intermediates that can be broken into 5 C sugars after adding 3C subunit

8. Regulating the Calvin Cycle Rubisco is main rate-limiting step indirectly regulated by light 2 ways 1) Rubisco activase 2) Light-induced changes in stroma a) pH b) [Mg 2+ ] c) CO 2 is an allosteric activator of rubisco that only binds at high pH and high [Mg 2+ ] also: stomates open in the light

9. Regulating the Calvin Cycle Several Calvin cycle enzymes (e.g.Fructose-1,6- bisphosphatase) are also regulated by thioredoxin contain disulfide bonds which get oxidized in the dark in light, ferredoxin reduces thioredoxin, thioredoxin reduces these disulfide bonds to activate the enzyme How light reactions talk to the Calvin cycle S - S 2Fd ox 2Fd red PSI + PSII light 2e- oxidized thioredoxin reduced thioredoxin S - S SH oxidized enzyme (inactive) reduced enzyme (active) SH

10. PHOTORESPIRATION Rubisco can use O 2 as substrate instead of CO 2 RuBP + O 2 3-phosphoglycerate + phosphoglycolate

11. PHOTORESPIRATION Rubisco can use O 2 as substrate instead of CO 2 RuBP + O 2 3-phosphoglycerate + Phosphoglycolate Releases CO 2 without making ATP or NADH

12. PHOTORESPIRATION Releases CO 2 without making ATP or NADH Called photorespiration : undoes photosynthesis

13. PHOTORESPIRATION Rubisco can use O 2 as substrate instead of CO 2 RuBP + O 2 3-phosphoglycerate + Phosphoglycolate C3 plants can lose 25%-50% of their fixed carbon

14. PHOTORESPIRATION Rubisco can use O 2 as substrate instead of CO 2 RuBP + O 2 3-phosphoglycerate + Phosphoglycolate C3 plants can lose 25%-50% of their fixed carbon Both rxns occur at same active site

15. PHOTORESPIRATION C3 plants can lose 25%-50% of their fixed carbon phosphoglycolate is converted to glycolate : poison!

16. Detoxifying Glycolate 1) glycolate is shuttled to peroxisomes

17. Detoxifying Glycolate 1) glycolate is shuttled to peroxisomes 2) peroxisomes convert it to glycine produce H 2 O 2

18. Detoxifying Glycolate 1) glycolate is shuttled to peroxisomes 2) peroxisomes convert it to glycine 3) glycine is sent to mitochondria

19. Detoxifying Glycolate 1) glycolate is shuttled to peroxisomes 2) peroxisomes convert it to glycine 3) glycine is sent to mitochondria 4) mitochondria convert 2 glycine to 1 serine + 1 CO 2 Why photorespiration loses CO 2

20. Detoxifying Glycolate 1) glycolate is shuttled to peroxisomes 2) peroxisomes convert it to glycine 3) glycine is sent to mitochondria 4) mitochondria convert 2 glycine to 1 serine + 1 CO 2 5) serine is returned to peroxisome

21. Detoxifying Glycolate 1) glycolate is shuttled to peroxisomes 2) peroxisomes convert it to glycine 3) glycine is sent to mitochondria 4) mitochondria convert 2 glycine to 1 serine + 1 CO 2 5) serine is returned to peroxisome 6) peroxisome converts it to glycerate & returns it to chloroplast

22. Detoxifying Glycolate Why peroxisomes are next to cp and mito in C3 plants Mitochondrion

23. Lipid metabolism Most are glycerolipids: fatty acids bonded to glycerol

24. GLYCEROLIPIDS Triacylglycerols = FAs on all 3 C store energy

25. GLYCEROLIPIDS Bond FA to glycerol Diacylglycerols = FAs on 2 Cs, headgroup on C 3

26. GLYCEROLIPIDS Diacylglycerols = FAs on 2 Cs, headgroup on C 3 Form bilayers in water

27. Lipid metabolism Unique aspects in plants Make fatty acids by same set of reactions, but in plastids with a prokaryotic fatty acid synthase 12 proteins, cf one multifunctional protein

28. Lipid metabolism Make fatty acids in plastids with a prokaryotic FAS 12 proteins, instead of one multifunctional protein Assemble some lipids in CP, others in ER

29. Lipid metabolism Make fatty acids in plastids with a prokaryotic FAS 12 proteins, instead of one multifunctional protein Assemble some lipids in CP, others in ER Acetyl-CoA carboxylase is also prokaryotic = 4 subunits, except in grasses (profoxydim & other grass herbicides inhibit ACCase)

30. Lipid metabolism Acetyl-CoA carboxylase is also prokaryotic = 4 subunits, except in grasses (profoxydim & other grass herbicides inhibit ACCase) Same biochem, but diff location and enzymes

31. Lipid metabolism Acetyl-CoA carboxylase is also prokaryotic = 4 subunits, except in grasses (profoxydim & other grass herbicides inhibit ACCase) Same biochem, but diff location and enzymes In light cp make lots of NADPH, and leaves are main sinks for FA

32. Lipid metabolism Acetyl-CoA carboxylase is also prokaryotic = 4 subunits, except in grasses (profoxydim & other herbicides inhibit ACCase) Same biochem, but diff location and enzymes In light cp make lots of NADPH, and leaves are main sinks for FA But, each cell makes its own FA, so NADPH in other cells comes from Pentose-Pi shunt

33. Lipid metabolism Source of acetyl-CoA is controversial Most comes from plastid PDH

34. Lipid metabolism Source of acetyl-CoA is controversial Most comes from plastid PDH Some comes from cytoplasmic acetate; activated in cp Also used to make sterols, some amino acids, many others

35. Lipid metabolism Source of acetyl-CoA is controversial Most comes from plastid PDH Some comes from cytoplasmic acetate; activated in cp Also used to make sterols, some amino acids, many others Why ACCase is “ committed step ”

36. Lipid metabolism Assemble some lipids in CP, others in ER “ 16:3 plants ” assemble lipids in cp using FA-ACP = prokaryotic pathway ( “ primitive ” )

37. Lipid metabolism “ 16:3 plants ” assemble lipids in cp using FA-ACP = prokaryotic pathway ( “ primitive ” ) “ 18:3 plants ” export FA, assemble lipids in ER using FA- CoA = eukaryotic pathway ( “ advanced ” )

38. Lipid metabolism “ 16:3 plants ” assemble lipids in cp using FA-ACP = prokaryotic pathway ( “ primitive ” ) “ 18:3 plants ” export FA, assemble lipids in ER using FA- CoA = eukaryotic pathway ( “ advanced ” ) Substrates for most desaturases are lipids, not FA!

39. Lipid metabolism Unique aspects in plants Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol

40. Lipid metabolism Unique aspects in plants Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol: saves PO 4

41. Lipid metabolism Unique aspects in plants Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol : saves PO 4 A) MGDG (Monogalactosyl diacylglycerol) 50% cp -> most abundant lipid on earth!

42. Lipid metabolism Unique aspects in plants Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol : saves PO 4 A) MGDG (Monogalactosyl diacylglycerol) 50% cp B) DGDG (Digalactosyl diacylglycerol) 28% cp

43. Lipid metabolism Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol : saves PO 4 A) MGDG (Monogalactosyl diacylglycerol) 50% cp B) DGDG (Digalactosyl diacylglycerol) 28% cp C) SQDG ( Sulphoquinovosyldiacylglycerol) 16% cp

44. Lipid metabolism Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol : saves PO 4 A) MGDG (Monogalactosyl diacylglycerol) 50% cp B) DGDG (Digalactosyl diacylglycerol) 28% cp C) SQDG ( Sulphoquinovosyldiacylglycerol) 16% cp Very unsaturated!

45. Lipid metabolism Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol : saves PO 4 A) MGDG (Monogalactosyl diacylglycerol) 50% cp B) DGDG (Digalactosyl diacylglycerol) 28% cp C) SQDG ( Sulphoquinovosyldiacylglycerol) 16% cp Very unsaturated! Makes membranes very fluid

46. Lipid metabolism Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol : saves PO 4 A) MGDG (Monogalactosyl diacylglycerol) 50% cp B) DGDG (Digalactosyl diacylglycerol) 28% cp C) SQDG ( Sulphoquinovosyldiacylglycerol) 16% cp Very unsaturated! Makes membranes very fluid Source of  3 FA

47. Lipid metabolism Unique aspects in plants 1)Make fatty acids in plastids 2)large amounts of galactolipids 3)Oleosomes: oil-storing organelles with only outer leaflet

48. Lipid metabolism Oleosomes: oil-storing organelles with only outer leaflet Put oils between the leaflets as they are made

49. Lipid metabolism Oleosomes: oil-storing organelles with only outer leaflet Put oils between the leaflets as they are made Add oleosin proteins to outside: curve the membrane

50. Lipid metabolism Oleosomes: oil-storing organelles with only outer leaflet Put oils between the leaflets as they are made Add oleosin proteins to outside: curve the membrane Oils often have unusual fatty acids

51. Lipid metabolism Use fats to store carbon as well as energy!!?? Recover C via glyoxylate cycle & gluconeogenesis

52. Lipid metabolism Biological roles Plasma membrane lipids help survive freezing

53. Lipid metabolism Biological roles Plasma membrane lipids help survive freezing Unacclimated cells vesiculate as they lose water & pop when it returns

54. Lipid metabolism Biological roles Plasma membrane lipids help survive freezing Unacclimated cells vesiculate as they lose water & pop when it returns Acclimated cells shrivel & reswell

55. Lipid metabolism Biological roles Plasma membrane lipids help survive freezing Mito lipid composition may also influence chilling sensitivity CS plants (eg bananas) are damaged at 10˚ C

56. Lipid metabolism Biological roles Plasma membrane lipids help survive freezing Mito lipid composition may also influence chilling sensitivity CS plants (eg bananas) are damaged at 10˚ C Mito show defects at <10˚ C not seen in other plants

57. Lipid metabolism CS plants (eg bananas) are damaged at 10˚ C Mito show defects at <10˚ C not seen in other plants Membrane lipids show phase changes at these T

58. Lipid metabolism CS plants (eg bananas) are damaged at 10˚ C Mito show defects at <10˚ C not seen in other plants Membrane lipids show phase changes at these T Blamed on saturated PG

59. Lipid metabolism Biological (& commercial) roles Plasma membrane lipids help survive freezing Mito lipid composition influences chilling sensitivity Mito show defects at <10˚ C not seen in other plants unsaturated FA did not fix CS, but saturated FA made it worse: reason for GM desaturases

60. Lipid metabolism Other commercial aspects Yield and quality of seed oil is very important:12 million tons/year

61. Lipid metabolism Other commercial aspects Yield and quality (especially unsaturation) of seed oil is very important:12 million tons/year Want more double bonds, especially  -3, for health Want less double bonds for shelf life and taste Each double bond increases p(oxidation) 40x

62. Lipid metabolism Other commercial aspects Yield and quality (especially unsaturation) of seed oil is very important:12 million tons/year Want more double bonds, especially  -3, for health Want less double bonds for shelf life and taste Each double bond increases p(oxidation) 40x Have GM oils with more & less double bonds

63. Lipid metabolism Other commercial aspects Yield and quality of seed oil is very important:12 million tons/year Also have markets for many specialized oils

64. Lipid metabolism Other commercial aspects Yield and quality of seed oil is very important Also have markets for many specialized oils Have genetically-engineered many crops to alter seed oils or produce specific fats

65. Lipid metabolism Biofuels are now very fashionable Biodiesel = fatty acid methyl esters Trans-esterify oils to make them volatile

66. Lipid metabolism Biofuels are now very fashionable Biodiesel = fatty acid methyl esters Trans-esterify oils to make them volatile Projected to be 10% of european diesel in 2015

67. Lipid metabolism Biofuels are now very fashionable Biodiesel = fatty acid methyl esters Trans-esterify oils, used cooking oil, etc Projected to be 10% of european diesel in 2010 Also use coconut & other oils directly in diesel engines

68. Lipid metabolism Also use coconut & other oils directly in diesel engines Just need to be sufficiently fluid to reach cylinder

69. Lipid metabolism Also use coconut & other oils directly in diesel engines Just need to be sufficiently fluid to reach cylinder Add double bonds to fatty acids or make them shorter