BIO 104 4/23/96

Photosynthesis
-carbon fixed into organic molecules
2 types of reactions
     1) light-dependant reactions
     In the light-dependent reactions, chlorophyll and other molecules in the
     membranes of the thylakoids capture sunlight energy and convert some of
     it into the chemical energy of ATP and NADPH2
     2) light independent reactions
     In the light-independent reactions, soluble enzymes in the stroma use the
     ATP and NADPH2 to drive the synthesis of glucose and other organic molecules.

SEE FIGURE 8.10     
Light in the form of photons
     1) photosystem I
     2) photosystem II
          -Chlorophyll-filled complexes embedded in the thylakoid membrane
           are what absorb the light during photosynthesis
               -different wavelengths are absorbed at 680nm (Photosystem II)
                and 700nm (photosystem I) 
          -Electrons are boosted out of the photosystem and reduce ferridoxin. 
           ferridoxin send the electrons through an electron carrier system
           and eventually reduce NADP to NADPH2
          -A photon of light excites an electron in PSII that is donated from
           P680 to photosystem I (PSI).
          -The electron uses its photon-contributed energy to drive a proton 
           pump and thus generate ATP.
          -Ferredoxin contributes two electrons to reduce NADP+ to NADPH.
          -the electrons that replace the ones boosted out chlorophyll come
           from the water; the water is split during photolysis
          -a membrane-bound proton protein pumps the protons into the interior
           of the thylakoids - then - protons go through the ATPase and form
           ATP from ADP in a process known as chemiosmosis.
               -3 products result from the light reaction:
                    1) oxygen gas
                    2) NADPH 
                    3) ATP
          NADPH and ATP are both used in light-independent reactions

DR. BARSTOW SHOWED A VIDEO ABOUT LIGHT -REACTIONS OF PHOTOSYNTHESIS

Light Independent Reactions
     CO2 fixation
     How is carbon fixed?
     "The Path of Carbon in Photosynthesis" by J.A. Bassham
     Carbon fixation was first examined in 1946
     What the scientist did:
          1. Used algae in a suspended state; which carries on 
               photosynthesis.
          2. They injected radioactive carbon into the algae suspension
          3. The carbon was taken up by the algae and fixed into sugars
               -dropped a sample into hot methanol and that fixes (stops)
               the reaction
               -use chromatography and trace where the molecules
               were located in the plant
     Calvin worked out the process by which carbon is fixed during photosynthesis
          -Calvin-Benson Cycle
          See worksheet given out in class or at BLC for a truly 
          better understanding of this process.
          RuBP most abundant protein in the world; located in the
               stroma
          Six RuBP molecules combines with six carbon dioxide
               molecules to produce twelve PGA molecules.
               -ATP gives a phosphate molecule to PGA to form
               diphosphoglycerate; which is reduced by NADPH to
               form twelve molecules of PGAL
               -PGAL forms two molecules of itself to form
               glucose and other sugars:  the remaining ten      
               molecules react with ATP to begin the cycle all 
               over again
          SEE FIGURE 8.12

Leaf Variations - C3 and C4 photosynthesis
C3 leaves are mostly dicots.
Tomorrow's lecture will be on C3, C4, and CAM photosynthesis.