Calvin Cycle Uses ATP and NADPH to convert CO 2 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 CO 2 acceptor is regenerated during the process 3 CO 2 molecules (and 3 cycles) are needed to produce on net G3P molecule

Calvin cycle

Calvin cycle-Carbon fixation Carbon from CO 2 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  New molecule is 1,3-Bisphosphoglycerate  Activated intermediate Electrons from NADPH are used to reduce 1,3- Bisphosphoglycerate  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 CO 2 come from Plants get CO 2 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 CO 2 molecules  Oxygen:CO 2 ration shifts Rubisco uses O 2 instead of CO 2  Eventually yields CO 2 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 CO 2 than Rubisco Adds Carbon from CO 2 onto PEP to form Oxaloacetate Eventually CO 2 is released into adjacent Bundle Sheath cell where Calvin takes place  Maintains high CO 2 to O 2 ratio in BSC  Rubisco can still use CO 2

C4 Plants

CAM Plants Pineapples, cacti and other succulents Similar to C4  Way to get around photorespiration Stomata open during night to take in CO 2  Carbon is stored in an organic acid molecule During daylight (when light cylce produces ATP and NADPH) organic acids degrade releasing CO 2 into the Calvin Cycle

Overview