AKA Light Independent Reactions

Melvin Calvin Identified the pathway in the 1950’s

The Calvin Cycle Rxn that converts CO 2 to G3P Called CO 2 Assimilation Occurs in the stroma of chloroplasts A cyclic series of rxn’s

The Calvin Cycle The rxn’s are indirectly dependent on light because the ATP and NADPH made during the light rxn fuel the Calvin Cycle.

The Calvin Cycle 3 Phases 1.Carbon Fixation 2.Reduction Reactions 3.Regeneration of RuBP

Phase 1: Carbon Fixation CO 2 (from atmosphere) joins with RuBP Forms unstable 6C compound

Phase 1: Carbon Fixation Immediately splits into 2 3C PGA’s Catalyzed by rubisco (a large enzyme, works very slowly – so many are needed)

Carbon Fixation

Phase 2: Reduction ATP donates Pi to PGA – makes PGAP (bisphosphoglycerate) NADPH (produced during Light Rxn) donates H + and 2e - to PGAP

Phase 2: Reduction Becomes NADP + again and returns to thylakoid membrane Donated H + reduces PGAP to PGAL (G3P)

Phase 2: Reduction One G3P exits here (will be used to make glucose, sucrose, starch)

Phase 3: RuBP Regeneration Complex series of rxns take remaining 5 G3P and rearrange them to make 3 RuBP 3 ATP are used

C 4 Plants  Many plants begin the Calvin Cycle with a 4 carbon compound instead of a 3 carbon compound.  They include grasses (sugar cane and corn). These plants live in areas that are very hot and semi-arid.