Photosynthesis

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Photosynthesis

  1. 1. PHOTOSYNTHESIS
  2. 2. CHLOROPLASTS <ul><li>Site of Photosynthesis </li></ul><ul><li>Double Membrane </li></ul><ul><li>Interior space called the STROMA </li></ul><ul><li>Columns of membrane bound sacs </li></ul><ul><ul><ul><li>Sacs = Thylakoids </li></ul></ul></ul><ul><ul><ul><li>Stacks = Grana </li></ul></ul></ul>
  3. 3. Membrane holding together Thylakoids & Grana is called the LAMELLAE
  4. 4. THYLAKOID MEMBRANE THYLAKOID SPACE or LUMEN
  5. 5. PIGMENTS ARE IMBEDDED IN THE MEMBRANE IN CLUSTERS CALLED PHOTOSYSTEMS
  6. 6. REMEMBER THAT VISIBLE LIGHT IS ONLY A SMALL PORTION OF THE ENERGY COMING FROM THE SUN THE AMOUNT OF ENERGY IN LIGHT IS DETERMINED BY ITS WAVELENGTH  THIS ALSO DETERMINES THE COLOUR OF LIGHT
  7. 7. THE JOB OF PIGMENTS IS TO ABSORB SPECIFIC WAVELENGTHS OR PHOTONS OF LIGHT. THIS ENERGY IS TRANSFERRED TO ELECTRONS  THESE ‘catching’ PIGMENTS ARE CALLED ANTENNA COMPLEXES
  8. 8. <ul><li>PHYTOL TAIL </li></ul><ul><li>ANCHORS PIGMENT INTO THE THYLAKOID MEMBRANE </li></ul><ul><li>PORPHRYIN RING </li></ul><ul><li>CENTRAL Mg </li></ul><ul><li>ABSORBS LIGHT ENERGY AND TRANSFERS IT TO AN ELECTRON </li></ul>
  9. 9. PHOTOSYNTHESIS OVERVIEW LIGHT REACTIONS DARK REACTIONS
  10. 10. LIGHT REACTIONS
  11. 11. THE EXCITED ELECTRONS THEN TRANSFER ENERGY FROM PIGMENT TO PIGMENT IN THE PHOTOSYSTEM UNTIL IT REACHES A REACTION CENTRE (chlorophyll a) AN ELECTRON IS THEN ‘KICKED’ TO A HIGHER E-LEVEL REDOX REACTIONS THEN MOVE THE ELECTRON TO A “PRIMARY ELECTRON ACCEPTOR” CALLED PLASTOQUINONE or PQ  I.O.U. CONCEPT !!!!!
  12. 12. <ul><li>THERE ARE 2 PHOTOSYSTEMS: </li></ul><ul><li>PI or P700 </li></ul><ul><li>ACTIVATED BY A PHOTON OF 700nm </li></ul><ul><li>PII or P680 </li></ul><ul><li>680nm PHOTON ACTIVATES IT </li></ul><ul><li>LIGHT HAS MUTLIPLE ENTRANCE PTS </li></ul><ul><li>SYSTEM MUST ALSO BE ‘RELOADED’ </li></ul>
  13. 14. ENERGY HAS BEEN TRANSFERRED FROM SOLAR OR RADIANT ENERGY (light) INTO CHEMICAL POTENTIAL ENERGY ( PQ ) JUST AS IN THE ETC IN RESPIRATION THE ELECTRONS ARE THEN MOVED FROM ONE PROTEIN TO ANOTHER ALONG THE MEMBRANE (PQ  CYTOCHROME COMPLEXES  PLASTOCYANIN Pc  P700  FERREDOXIN Fd) THIS CAUSES H+ TO BE PUMPED INTO THE LUMEN
  14. 15. EVENTUALLY THE ELECTRONS REACH NADPH REDUCTASE – WHICH ATTACHES THE ELECTRONS AND SOME H+ TO NADP+ CREATING NADPH H+ THAT BUILDS UP IN THE LUMEN CREATE AN ELECTROCHEMICAL GRADIENT . AS THIS EQUALIZES THE H+ PASS THROUGH ATP Synthase AND CATALYZE ADP + Pi  ATP
  15. 17. “ Z DIAGRAM” A B
  16. 18. “ Z DIAGRAM”
  17. 20. <ul><li>A – NON-CYCLIC e- FLOW </li></ul><ul><li>A Z-PROTEIN SPLITS H20 AND THE ELECTRONS THEN REPLENISH THOSE LOST BY P680 (PHOTOSYSTEM II) AND OXYGEN IS CREATED AS WASTE </li></ul><ul><li>CALLED NON-CYCLIC BECAUSE THE ORIGINAL ELECTRONS ARE NOT RETURNED TO P680 </li></ul>
  18. 21. <ul><li>B – CYCLIC ELECTRON FLOW </li></ul><ul><li>SOME LIGHT WILL ONLY ACTIVATE PHOTOSYSTEM I (P700) </li></ul><ul><li>THE ELECTRON IS DOES NOT GET USED TO MAKE NADPH BUT IT DOES HELP SYNTHESIZE ATP </li></ul><ul><li>INSTEAD IT IS RETURNED TO REPLENISH PHOTOSYSTEM I (P700) </li></ul>
  19. 23. PHOTOSYNTHESIS OVERVIEW LIGHT REACTIONS DARK REACTIONS
  20. 24. DARK REACTIONS
  21. 25. <ul><li>DARK REACTIONS/CALVIN CYCLE </li></ul><ul><li>OCCURS IN THE STROMA </li></ul><ul><li>CYCLIC PROCESS INVOLVED IN CARBON FIXATION  ABSORBING C02 FROM THE AIR AND ATTACHING IT TO ORGANIC MOLECULES </li></ul><ul><li>OCCURS IN 3 PHASES: </li></ul><ul><ul><li>CARBON FIXATION </li></ul></ul><ul><ul><li>REDUCTION </li></ul></ul><ul><ul><li>REGENERATION OF RuBP </li></ul></ul>
  22. 27. <ul><li>CARBON FIXATION </li></ul><ul><li>CO2 COMES INTO THE STROMA FROM THE LEAVES </li></ul><ul><li>3 CO 2 BINDS TO 5 EXISTING RuBP ( 5C ) TO FORMS 3 UNSTABLE 6C MOLECULE AND EACH SPLITS INTO TWO 3-PG’S ( 3C ) </li></ul><ul><li>3 CO2 + 3 x RuBP ( 5C )  3 x 2 3-PG ( 3C ) </li></ul>RuBP 3-PG
  23. 28. THE ENZYME RUBISCO CATALYZES THE FIXATION OF ATMOSPHERIC CO2 INTO THE TWO 3-PG MOLECULES IT WORKS VERY SLOWLY AND MANY COPIES ARE NEEDED TO MAKE THE PROCESS POSSIBLE RUBISCO MAY ACCOUNT FOR UP TO ½ THE PROTEIN IN A LEAF  EXTREMELY ABUNDANT
  24. 29. C-FIXATION RUBSICO REDUCTION REGENERATION
  25. 30. <ul><li>REDUCTION </li></ul><ul><li>ATP DONATES A P TO EACH 3-PG </li></ul><ul><li>3-PG BECOMES 1,3-BPG </li></ul><ul><li>1,3-BPG IS THEN REDUCED BY NADPH LOSES THE P AND GAINS A H+ TO BECOME G3P </li></ul><ul><li>STARTED WITH 6 3-PG’s  6 G3P’s </li></ul><ul><li>5 GO ON TO REGENERATE … 1 GOES ON TO BECOME PART OF GLUCOSE </li></ul>
  26. 31. C-FIXATION RUBSICO REDUCTION REGENERATION
  27. 32. <ul><li>REGENERATION OF RuBP </li></ul><ul><li>G3P THEN GETS A P FROM ATP TO PRODUCE RuBP WHICH REACTIVATES THE CALVIN CYCLE </li></ul><ul><li>SIMILAR IDEA TO THE KREB’s CYCLE AND REGENERATING OXALOACETATE </li></ul>
  28. 33. C-FIXATION RUBSICO REDUCTION REGENERATION C3 PHOTOSYNTHESIS
  29. 34. FATE OF G3P <ul><li>MADE INTO GLUCOSE BY A SERIES OF ENZYMES </li></ul><ul><li>GLUCOSE CAN THEN BE CONVERTED TO: </li></ul><ul><ul><ul><li>CELLULOSE (CELL WALLS) </li></ul></ul></ul><ul><ul><ul><li>STARCH (STORAGE) </li></ul></ul></ul><ul><ul><ul><li>USED IN CELL RESPIRATION </li></ul></ul></ul>
  30. 35. TWISTS
  31. 36. <ul><li>NOT ALL PLANTS DO THE CALVIN CYCLE THE SAME WAY  RUBISCO ISN’T AS EFFECTIVE AT HIGHER TEMPERATURES… LEAVES BUILT TO REDUCE H20 LOSS </li></ul><ul><li>SEVERAL TYPES OF PLANTS DO C4 Photosynthesis </li></ul><ul><li>C4 PLANTS USE A DIFFERENT ENZYME ( PEP CARBOXYLASE ) TO FIX C02 TO A MOLECULE CALLED PEP  RESULTS IN OXALOACETATE (4C) </li></ul><ul><li>ORGANIC ACIDS ARE THEN MOVED INTO THE C3 PATHWAY </li></ul>
  32. 37. IN PLANTS WHERE H20 LOSS IS A SERIOUS PROBLEM (DESERT PLANTS) CAM PHOTOSYNTHESIS OCCURS LEAVES OPEN AT NIGHT AND STORE C02, DO C-FIXATION AND THEN STORE THE C4 PRODUCTS TO BE USED DURING THE DAY IN THE CALVIN CYCLE (C3)
  33. 38. THE END

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