Review

C. The Calvin cycle occurs in the stroma 1. Phase 1: carbon fixation 2. Phase 2: reduction reactions 3. Phase 3: RuBP regeneration

CALVIN CYCLE ____ x C-C-C—P __ x C-C-C—P glucose ____ x P--C-C-C-C-C—P ____ x [3-PGA] __ x C-C-C—P [G-3-P] glucose ____ x C-C-C—P ____ x P--C-C-C-C-C—P ribulose biphosphate ___ x ADP ___ x ATP ___ Pi ___ H2O CALVIN CYCLE O=COH HCOH H2C—O—P O=C—O—P HOCH ____ x [G-3-P] O=CH [1,3-BPG]

1. Phase 1: carbon fixation CALVIN CYCLE 1. Phase 1: carbon fixation 6 x CO2 6 x H20 O=COH HCOH H2C—O—P 12 x 3-phosphoglycerate [3PGA]

1. Phase 1: carbon fixation a CO2 is added to a 5-C ribulose biphosphate (RuBP) to form a 6-carbon intermediate this unstable intermediate immediately splits into two 3-C molecules of 3-phosphoglycerate (3-PGA) enzyme involved  ribulose biphosphate carboxylase (rubisco), a very large and slow-working enzyme this process happens 6 times to make one glucose, 6 x (5-carbon) RuBP + 6CO2  12 x (3-carbon) 3PGA this process is called C3 photosynthesis because the first product of fixation is a 3-carbon molecule

Pi 2 CALVIN CYCLE O=COH HCOH H2C—O—P 12 x ATP 12 x ADP O=C—O—P HOCH 12 x [3-phosphoglycerate 3-PGA] 12 x ATP 12 x ADP O=C—O—P HOCH H2C—O—P 12 x 1,3-biphosphoglycerate [1,3-BPG] 12 x NADPH +H+ Pi 12 x NADP+ 12 X glyceraldehyde-3-phosphate [G-3-P] O=CH HOCH H2C—O—P 2 x C-C-C—P [G-3-P] glucose

2. Phase 2: reduction reactions a series of reactions that are essentially the reverse of glycolysis 3PGA is phosphorylated to biphosphoglycerate (1,3-BPG) using ATP 1,3-BPG is reduced to glyceraldehyde-3-phosphate (G3P) by NADPH + H+ (and a Pi is lost) 1 molecule of G-3-P leaves the cycle for every 5 molecules of G3P that go on 2 molecules of G3P will combine to make 1 glucose

CALVIN CYCLE 6 10 x P--C-C-C-C-C—P ribulose biphosphate [RuBP] 6 x ADP 6 x ATP 4 Pi 4 H2O 10 x C-C-C—P G-3-P

3. Phase 3: RuBP regeneration 10 molecules of 3-C G3P are converted into 6 molecules of 5-C RuBP we start with 10 phosphates (1 per G3P) and must end with 12 (2 per RuBP) in the process 4 Pi are removed and 6 ATP are consumed 4 H2O must be added for the H and OH groups to add to the molecules

4. Overall equation 6CO2 + 18ATP + 12(NADPH + H+) + 10H2O + 6RuBP  18ADP + 16Pi + 12NADP+ + 6RuBP + 2 G3P

5. Fate of G3P chloroplast G-3-P glucose starch glucose cellular respiration sucrose cellulose transported to other parts of plant (translocation) starch (storage)