PHOTOSYNTHESIS - AUTOTROPHIC METABOLISM            

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

   µ  assumption: a mutant metazoan cell whose hemoglobin's can capture light energy
  plant photosynthetic rates =  20 mg hexose/dm2/ hr
  average human surface area =  170 dm2
  hexose productivity =  [170 x 20 = 3.4gm/hr] x 12hr  =   40.8 gm/d 
  1 mole glucose =  183 gm  =  686Kc/mol
  green man productivity =    41 gm  =   153 Kc/mol
  BMR =  2,000 Kc/d   = about 8.5 % of need

         We Evolve   =  increased surface area, remain sessile,
                                 peristalsis becomes vestigial, circulation is replaced,
tulip - next page                                                                                 ........................ 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 bonds          

         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

rose - next page                   Student CD Activity 10.1 Overview of Photosynthesis

*

 

 

 

 

  

 

 

 
 
so...  What are the 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
peony - next page                     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  +  NADPH  -->    PGAL
                     
regeneration         of  RuBP  via  HMP  pathway
pansy - next page     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* 

iris - next page                                                      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
flower - next page     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  
blue bell - next page                      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
  
                5.
PHOTOIONIZATION - takes part in photochemical reactions
lilly - next page                                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 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, but no NADPH )
  
                Chemiosmosis* (making H+ gradient)  &   Cellular Locations of the Photosystems
geranium - next page         ATP-synthase* making ATP (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*   &   C
14intermediates*
  

  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 

daffodil - next page                                                                 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
   
            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
               
temporal separation, not spatial differences
          
SUMMARY OF PHOTOSYNTHESIS*                   Concept Activity 10.4 - Photosynthesis in Dry Climates
                                                             
         
peony - next page NEXT LECTURE - CELL DIVISION                              a paradigmkey concepts*

 

 

 

 

 

 

 

 

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