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Photosynthesis

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  • 1. PHOTOSYNTHESIS
  • 2. CHLOROPLASTS
    • Site of Photosynthesis
    • Double Membrane
    • Interior space called the STROMA
    • Columns of membrane bound sacs
        • Sacs = Thylakoids
        • Stacks = Grana
  • 3. Membrane holding together Thylakoids & Grana is called the LAMELLAE
  • 4. THYLAKOID MEMBRANE THYLAKOID SPACE or LUMEN
  • 5. PIGMENTS ARE IMBEDDED IN THE MEMBRANE IN CLUSTERS CALLED PHOTOSYSTEMS
  • 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. 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.
    • PHYTOL TAIL
    • ANCHORS PIGMENT INTO THE THYLAKOID MEMBRANE
    • PORPHRYIN RING
    • CENTRAL Mg
    • ABSORBS LIGHT ENERGY AND TRANSFERS IT TO AN ELECTRON
  • 9. PHOTOSYNTHESIS OVERVIEW LIGHT REACTIONS DARK REACTIONS
  • 10. LIGHT REACTIONS
  • 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.
    • THERE ARE 2 PHOTOSYSTEMS:
    • PI or P700
    • ACTIVATED BY A PHOTON OF 700nm
    • PII or P680
    • 680nm PHOTON ACTIVATES IT
    • LIGHT HAS MUTLIPLE ENTRANCE PTS
    • SYSTEM MUST ALSO BE ‘RELOADED’
  • 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
  • 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
  • 16.  
  • 17. “ Z DIAGRAM” A B
  • 18. “ Z DIAGRAM”
  • 19.  
  • 20.
    • A – NON-CYCLIC e- FLOW
    • A Z-PROTEIN SPLITS H20 AND THE ELECTRONS THEN REPLENISH THOSE LOST BY P680 (PHOTOSYSTEM II) AND OXYGEN IS CREATED AS WASTE
    • CALLED NON-CYCLIC BECAUSE THE ORIGINAL ELECTRONS ARE NOT RETURNED TO P680
  • 21.
    • B – CYCLIC ELECTRON FLOW
    • SOME LIGHT WILL ONLY ACTIVATE PHOTOSYSTEM I (P700)
    • THE ELECTRON IS DOES NOT GET USED TO MAKE NADPH BUT IT DOES HELP SYNTHESIZE ATP
    • INSTEAD IT IS RETURNED TO REPLENISH PHOTOSYSTEM I (P700)
  • 22.  
  • 23. PHOTOSYNTHESIS OVERVIEW LIGHT REACTIONS DARK REACTIONS
  • 24. DARK REACTIONS
  • 25.
    • DARK REACTIONS/CALVIN CYCLE
    • OCCURS IN THE STROMA
    • CYCLIC PROCESS INVOLVED IN CARBON FIXATION  ABSORBING C02 FROM THE AIR AND ATTACHING IT TO ORGANIC MOLECULES
    • OCCURS IN 3 PHASES:
      • CARBON FIXATION
      • REDUCTION
      • REGENERATION OF RuBP
  • 26.  
  • 27.
    • CARBON FIXATION
    • CO2 COMES INTO THE STROMA FROM THE LEAVES
    • 3 CO 2 BINDS TO 5 EXISTING RuBP ( 5C ) TO FORMS 3 UNSTABLE 6C MOLECULE AND EACH SPLITS INTO TWO 3-PG’S ( 3C )
    • 3 CO2 + 3 x RuBP ( 5C )  3 x 2 3-PG ( 3C )
    RuBP 3-PG
  • 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
  • 29. C-FIXATION RUBSICO REDUCTION REGENERATION
  • 30.
    • REDUCTION
    • ATP DONATES A P TO EACH 3-PG
    • 3-PG BECOMES 1,3-BPG
    • 1,3-BPG IS THEN REDUCED BY NADPH LOSES THE P AND GAINS A H+ TO BECOME G3P
    • STARTED WITH 6 3-PG’s  6 G3P’s
    • 5 GO ON TO REGENERATE … 1 GOES ON TO BECOME PART OF GLUCOSE
  • 31. C-FIXATION RUBSICO REDUCTION REGENERATION
  • 32.
    • REGENERATION OF RuBP
    • G3P THEN GETS A P FROM ATP TO PRODUCE RuBP WHICH REACTIVATES THE CALVIN CYCLE
    • SIMILAR IDEA TO THE KREB’s CYCLE AND REGENERATING OXALOACETATE
  • 33. C-FIXATION RUBSICO REDUCTION REGENERATION C3 PHOTOSYNTHESIS
  • 34. FATE OF G3P
    • MADE INTO GLUCOSE BY A SERIES OF ENZYMES
    • GLUCOSE CAN THEN BE CONVERTED TO:
        • CELLULOSE (CELL WALLS)
        • STARCH (STORAGE)
        • USED IN CELL RESPIRATION
  • 35. TWISTS
  • 36.
    • NOT ALL PLANTS DO THE CALVIN CYCLE THE SAME WAY  RUBISCO ISN’T AS EFFECTIVE AT HIGHER TEMPERATURES… LEAVES BUILT TO REDUCE H20 LOSS
    • SEVERAL TYPES OF PLANTS DO C4 Photosynthesis
    • C4 PLANTS USE A DIFFERENT ENZYME ( PEP CARBOXYLASE ) TO FIX C02 TO A MOLECULE CALLED PEP  RESULTS IN OXALOACETATE (4C)
    • ORGANIC ACIDS ARE THEN MOVED INTO THE C3 PATHWAY
  • 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)
  • 38. THE END