1. C-3

1. Calvin (Nobel prize 1961) found first stable substance formed after CO2 was incorporated into a molecule was a three carbon acid called 3-phosphoglyceric acid (3-PGA).

1. Looked for 2 carbon compound but found a 5 carbon sugar, phosphorylated at each end.
   
   
   1. Ribulose-1,5-bisphosphate (RuBP)
      

1. Reaction was catalyzed by ribulose
   bisphosphate carboxylase (rubisco)
   
   
2. Reaction is irreversible.
   
   
3. Most abundant protein on earth
   
   

1. Where does the RuBP come from?
   
   1. Calvin and coworkers worked out the C-3 photosynthetic carbon reduction cycle.
      
   2. Named for first product 3-PGA
      
   3. Calvin cycle PCR cycle occurs in stroma of chloroplast
      
2. Three main parts to PCR cycle
   1. Carboxylation
      1. CO2 + RuBP 2 (3-PGA)
         
         
         
         
         
         
         
         
         
   2. Reduction
      1. 3-PGA + 2 ATP + 2 NADPH
         

2 3-PGaldehyde + 2 ADP + 2 NADP

1. NOTE to fix (reduce) 1 molecule of CO2 must use
   1. ATP
   2. NADPH the reducing agent
   3. COMES FROM THE LIGHT REACTIONS
      
      
      
      
      
      
      
      
      
      

1. Regeneration
   
   1. RuBP is regenerated via a series phosphlorylated, 4, 5, 6, & 7 carbon sugars.
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
      
   2. Final reaction:
      1. Ribulose-5-P + ATP RuBP
      2. The ATP comes from Light Reactions
         
   3. ******Important Point******
      1. It requires three turns of Calvin cycle to fix 3 CO2 There is a net yield of one 3-PGaldehyde (Count the carbons)
      2. This molecule is what is used to synthesize sugars and starch.
      3. Stay tuned next semester.

1. Summary:

1. 6 CO2 + 12 H2O + 18 ATP + 12 NADPH

C6H12O6 + 6O2 + 6H2O + 18 ADP + 12 NADP

1. C-4
   
   1. Mid 60's Hatch and Slack found that sugar cane and other monocots first fixed in a 4-carbon acid (malic or aspartic)

1. Fixation (reduction) is preceded by a carboxylation with phosphoenlpyruvate (PEP) to form oxaloacetate (OAA) + Pi
   1. Reaction is catalyzed by PEP carboxylase
   2. Occurs in mesophyll cells
   3. In cytosol outside chloroplast
   4. PEP + CO2 OAA + Pi
      
2. Division of labor: Kranz anatomy (diagram)
   1. Mesophyll cells
      1. CO2 fixed in mesophyll cells
      2. OAA reduced by NADPH to produce malic acid (malate)
         1. OAA + NADPH malate + NADP
         2. NADPH (reducing power) comes from light reactions.
      3. OAA can be transaminated to aspartic acid
         
         
         
   2. Bundle sheath
      
      1. Malate or aspartate transported to bundle sheath cells
      2. Acid undergoes oxidative decarboxylation
         1. Malate + NADP CO2 + Pyruvate + NADPH
      3. CO2 refixed via Calvin C-3 cycle
      4. Pyruvate moves back to mesophyll and is phosphorylated with ATP to regenerate PEP
         1. Pyruvate + ATP PEP + AMP + Ppi
         2. It takes equivalent of 2ATP more to fix CO2 via C4
            

1. Crassulacean Acid Metabolism: CAM
   1. Found in succulents such as Crassulaceae, Cactaceae Euphorbiaceae and a few others.
      1. Grow mainly in hot dry climates
      2. Diurnal changes in acidity noted.
         1. Mostly malate
            
            
            
            
            
            
            
            
            
      3. Stomata open at night, closed during the day.
         
   2. The process:
      1. NIGHT
         1. Starch is degraded to PEP
         2. PEP-ase in cytosol carboxylates CO2 to PEP to form OAA
         3. OAA is reduced by NADH or NADPH to yield malic acid
         4. Malic acid diffuses into vacuole
         5. Concentrations can be > .3 M
            1. < cells take up water.
               
      2. DAY
         1. Malic acid diffuses out of vacuole and is oxidativatively decarboxylated to pyruvate
            
            1. Pyruvate converted to PEP and metabolized (e.g. back to starch)
               
         2. CO2 is refixed via C3 Calvin cycle
         3. Both processes occur in same cell - separated by time rather than space.