Calvin Cycle Uses ATP and NADPH to convert CO2 to glucose or other sugars Glyceraldehyde-3-phosphate is final product of Calvin cycle G3P can easily be converted to glucose or other sugars Cycle because CO2 acceptor is regenerated during the process 3 CO2 molecules (and 3 cycles) are needed to produce on net G3P molecule Calvin cycle Calvin cycle-Carbon fixation Carbon from CO2 is added to organic acceptor and can then be used for synthesis Ribulose biphosphate (RuBP) is the acceptor 5 carbon sugar Rubisco (Ribulose biphosphate carboxylase) is the enzyme that adds the new carbon to RuBP Most common enzyme on earth Results in a 6 carbon molecule that immediately degrades into two three carbon molecules-3 phosphoglycerate s has carboxyl group Calvin Cycle-Reduction ATP is used to phosphorylate 3-Phosphoglycerate Electrons from NADPH are used to reduce 1,3Bisphosphoglycerate New molecule is 1,3-Bisphosphoglycerate Activated intermediate Results in a carbonyl group Sugars have carbonyl group G3P is produced and it is a 3 carbon sugar For every 6 G3P molecules produced-5 are recycled and one can be used for anabolic rxns Calvin Cycle-Regeneration Uses 5 molecules of G3P to produce 3 molecules of RuBP Requires ATP to perform this task This is why more ATP is needed than NADPH Without regeneration of G3P, this would not be a cyclical reaction RuBP is ready to act as Carbon acceptor for fixation stage Where does CO2 come from Plants get CO2 from air via stomata Have guard cells that open and close stomata Also guard against loss of water vapor Photorespiration Happens in many plants during hot daytime conditions-soybeanss Guard cells close stomata to prevent water loss Unable to take up new CO2 molecules Oxygen:CO2 ration shifts Rubisco uses O2 instead of CO2 Eventually yields CO2 for Calvin cycle but so much effort was expended it is a net loss for plant C4 Plants Way to avoid photorespiration Takes place in grasses like corn Two types of tissue for photosynthesis First acts like antechamber-Mesophyll cell PEP carboxylase has higher affinity for CO2 than Rubisco Adds Carbon from CO2 onto PEP to form Oxaloacetate Eventually CO2 is released into adjacent Bundle Sheath cell where Calvin takes place Maintains high CO2 to O2 ratio in BSC Rubisco can still use CO2 C4 Plants CAM Plants Pineapples, cacti and other succulents Similar to C4 Stomata open during night to take in CO2 Way to get around photorespiration Carbon is stored in an organic acid molecule During daylight (when light cylce produces ATP and NADPH) organic acids degrade releasing CO2 into the Calvin Cycle Overview