LITTLE GREEN MEN - Why do animal cells not photosynthesize ???
                  chlorophyll*       vs.      hemoglobin             [leghemoglobin] 

         We Evolve   =  increased surface area, remain sessile,
                                 peristalsis becomes vestigial, circulation is replaced,
                                                                                 ........................ We are a plant ?

 
  what is   PHOTOSYNTHESIS...     a light driven phosphorylation
                                                                   ADP  +  P  --->  ATP
    ...it's AUTOTROPHIC Metabolism that occurs in organisms,
         which produces all their organic nutrients from inorganic
         materials thru conversion of light energy into covalent bond energy

a. chemotrophic... oxidation of small inorganics          b. phototrophic ... use light energy to make organics      so... What is PHOTOSYNTHESIS?            it's a cellular process - it requires a living cell...            procaryotes - bacteria,  blue-greens [cyanobacteria],            eucaryotes - all cells with  chloroplasts                    Student CD Activity 10.1 Overview of Photosynthesis

*

 
 so...  What are the molecular processes within Photosynthesis ?
      
          a.   capture of light energy via pigment molecules -
                       chlorophylls & accessory pigments (carotenes & phycobilins)
 
          b.   a  REDOX reaction -
                       produces oxidizing power = O₂   [ PHOTOLYSIS = splits water]
                       captures e- into cytochromes, plant ETC-like carrier proteins, and
                       it produces reducing power = NADPH         [just like NADH, but w P]
 
          c.  production of ATP via photophosphorylation
                       couples e- transfer to H+ gradients  &  ATP synthase   [ADP + P = ATP ]
    
          d.  reduction of  CO₂  to  CH₂O
                              6CO₂    +   12 H₂O*  <--->    C₆H₁₂O₆   +    6H₂O    +  6O₂*
                                CO₂    +     2H₂A     <--->      CH₂O       +      H₂O    +   2A
                     Source C   +  e^- donor                organic C            oxidized donor

 
 2 Fundamental Reaction Mechanisms of Photosynthesis

LIGHT Reactions - photochemical reactions              molecular excitation of chlorophyll by light results in                     a charge (+) separation across a membrane, with                     generation of proton motive force ( H+ gradient),                     & reduction of NADP via an ETC to NADPH

        DARK Reactions - thermochemical reactions
             carbon dioxide reduction (fixation) -  occurs in 3 stages
                      carboxylation        CO₂ +  RuBP  (5c)        -->    2 PGA (3c)
                      reduction               of  PGA  by  NADPH  -->    PGAL
                      regeneration         of  RuBP  via  HMP  pathway
     Overview figure*      Student CD Activity - 10.2 - The Light Reactions 

 Morphological Basis of Photosynthesis...   the CHLOROPLAST

     PLASTIDS - double unit membrane bound organelles
                           classified by pigment content (functional)

        PROPLASTIDS*...   in MERISTEMATIC cells give rise to all other plastids

            LEUCOPLASTS - amyloplasts - synthsize & store starch
                                         aleuoplasts - contain stored protein (crystals)
                                         elaioplasts contain oil & fat globules - fat biosynthesis

             CHROMOPLASTS -  found in flower petals, ripe fruit, scenescent leaves

             CHLOROPLASTS  -  MORPHOLOGICAL BASIS of photosynthesis* 

                                                      Concept Activity - 10.1 - The Sites of Photosynthesis

 
     Leaf Structure & the CHLOROPLAST* - ubiquitious to all green plants
    
        SHAPE - variable (elipsoid to ovoid; lenticular, stellate, convex)
        SIZE - 2 to 3 um dia by 5 to 10 um long
        NUMBER - 15 to 20 per mesophyll cell    [up to 400,000/cc]
        VOLUME - often larger than mitochondria

    CHLOROPLASM - (stroma) contains...
                pyrenoids* - which are starch coated protein granules
                70s (prokaryotic size) ribosomes
                naked DNA -  2 to 10^-15  (fentograms)  of DNA/chlp
                                  about equal to a bacterial cell's DNA
                                  highly supercoiled & repetitive (6 copies) DNA
                enzymes of CO₂ fixation and lipid droplets
     THYLAKOID*  Membranes*     =    LIGHT ABSORPTION
    

PIGMENTS of Photosynthesis -               Investigation - Chapter 10.2 - Paper Chromatography & Pigments
    Accessory Pigments - any non-chlorophyll pigments that absorb light
                Carotenoids - carotenes*   and    xanthophylls*
                Phycobilins - chromophore group (straight porphyrin) + a protein
                                        phycoerythrin   &    phycocyanin  - pigments of algae
 
    Chlorophylls - a,b,c,d, etc... [embedded in thylakoid disk membranes]*

       ELECTROMAGNETIC SPECTRUM*  (wave sizes & wavelength)   &   LIGHT ABSORPTION* 
                                    Concept Activity 10.2 - Light Energy and Pigments
                    ABSORPTION SPECTRA   - plot of amount light absorbed vs. wavelength  
                                 spectrophotometer*,       [ Spectronic  20   & cuvettes ]

                    ACTION SPECTRA*   - plot of physiological activity [O₂ released] vs. wavelength  
                     Engelman  experiment* (pic 2)   &   human Rod & Cone cells  &  rhodopsin curve*
                                                                     

Molecular Excitation of Chlorophyll      ABSORPTION of Light Energy ... blue light and red light               results in electrons being excited into higher orbitals

      FATES of Absorbed Energy -  PHOTOEXCITATION
     
                1. reradiates as vibrational heat*
  
                2. reradiated as fluorescence*   
  
                3. reradiated as phosphorescence (slower far red light emission)
  
                4. induced resonance* - vibrational  e^- excitation is passed
  
                5. PHOTOIONIZATION - takes part in photochemical reactions
                                electron is passed to an acceptor = ionized chl+

The LIGHT REACTIONS...    (or photoionization)  takes place in...
                                                                 Student CD Activity - 10.2 - The Light Reactions  
   
   PHOTOSYSTEMS -   protein & pigment complexes that catalyze photosynthesis   
                 -   include: chlorophylls, reaction center molecules, primary e^- acceptors   
                 -   two:   PS 1  and  PS 2 (photosystems, aka - Light Harvesting Complexes*)
 
        PS 1 -  [p700 rx center]  captures e- into coenzyme NADP+ making NADPH
 
        PS 2 - [p680 rx center]  -  splits water (photolysis) releasing  O₂  &  H⁺    

Path of the e- in the Photosystems    ( non-cyclic*        vs.        cyclic* )                                                      (   ATP + NADPH                  ATP, but no NADPH )
Chemiosmosis* (making H+ gradient)   &   Cellular Locations of the Photosystems
	ATP-synthase* making ATP (is just like in mitochondria)
	compare locations* in chloroplasts vs mitochondria     &      PS locations
	john kyrk's animation of light reactions         Sumanas, Inc. animation - light rx photosynthesis

  
DARK REACTIONS   
                    occur in chloroplasm  (stroma)
                    consumes the ATP  &  NADPH made in light reactions
                    reduces (CO₂ fixation = reduction)   CO₂  into  CH₂O   (sugars)
                    biochemical pathway =  Mel Calvin's  lollipop*   &   C¹⁴intermediates*
  
  C3 - CALVIN cycle*      ... it's reverse of glycolysis
             1 CO₂   +   5C RuBP    --->    (2) 3C sugars (PGA)            (Quicktime Movie*)
             (2) 3C sugars combine  (via back reaction of glycolysis)  --->   1 net glucose
             RuBP carboxylase   (Rubisco - an enzyme that feeds CO₂ into foods)
             Photo-Respiration - O₂ inhibition* of Rubisco;  a process that releases CO₂ 

       In additional to Calvin, there are two (2) additional pathways to make sugar 

	john kyrk's animation of dark reactions
	Student CD Activity - 10.3 The Calvin Cycle

   
   
 C4 - Hatch & Slack pathway*  
               1 CO₂  +  3C PEP  combine into --->   4C acid [OAA]  (in mesophyll cells)
               4C acid    --->    breaks down into 3C + CO₂  (in bundle sheath cells)
               & this CO₂ is now fixed into CH₂O in the Calvin cycle   (as described above)
               Different leaf anatomy  C3-anatomy*  vs.   C4-anatomy*
               PEP Carboxylase - produces 4C acid OAA (recall Krebs)
                       also an enzyme in bacteria & plants that makes oxaloacetate from PEP & CO₂    
           µ pathway results in spatial separation of acid & sugar production

 C4  -  CAM Pathway*  
                in succulents (Crassulacea family) and plants as pineapple
                same as C4, but it is within the same cell
           µ temporal separation, not spatial differences
                   SUMMARY OF PHOTOSYNTHESIS*         Concept Activity 10.4 - Photosynthesis in Dry Climates
                                                             
          NEXT LECTURE - CELL DIVISION                              key concepts*

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