The Calvin Cycle

1. The Calvin Cycle Part II of Photosynthesis

2. Calvin • Named after American biochemist Melvin Calvin • Most commonly used pathway by most plants • Calvin cycle is used by plants that are called C3 because of the 3-Carbon molecules that are made

3. Photosynthesis • Light-independent reaction (Dark Reaction) • Does not require light • Calvin Cycle • Occurs in stroma of chloroplast • Requires CO2 • Uses ATP and NADPH as fuel to run • Makes glucose sugar from CO2 and Hydrogen

4. Calvin Cycle • The Calvin cycle uses products from the light reactions + CO2 to make sugars and other compounds • What are the products of the light reactions? • Where does the CO2 come from?

6. Calvin Cycle • CO2 is changed to sugar in a series of chemical reactions: • CO2 + RuBP  6-Carbon molecule • RuBP = 5 Carbon sugar • The Enzyme that catalyzes this reaction is rubisco = the most abundant protein in nature(25%)

7. Step 1 • CO2 is diffused into the stroma of the chloroplast • A 5-Carbon molecule named RuBP combines to the CO2 • This becomes a 6-Carbon molecule that is very unstable • Split to become two 3-Carbon molecules called 3-phosphoglycerate (3-PGA) • 6-Carbon Sugar  3-PGA + 3-PGA

8. Step 2 • 3-PGA is still unstable • 3-PGA  glyceraldehyde 3-phosphate (G3P) • For this to occur, each3-PGA molecule gets a phosphate from ATP and a proton from NADPH • Once the molecule receives the P and proton it converts into G3P

10. 3-PGA + P + H  G3P Where did the P and H come from? *ATP ADP + P *NADPH  NADP+ + H

11. Step 3 • One G3P molecule leaves the Calvin cycle • This will be used to make a carbohydrate later

12. Step 4 • Other G3P molecule gets converted BACK to RuBP due to an addition of another phosphate from ATP • G3P + P  RuBP • This RuBP goes back to the Calvin cycle to be fixed again

14. Photosynthesis Formula Light energy 6CO2 + 6H2O  C6H12O6 + 6O2

15. Redox Reactions Reduction • Gain electrons Oxidation • Loses electrons

16. Oxidation Reaction • Loss of electrons from a substance in a chemical reaction • What molecules were oxidized during photosynthesis?

17. Reduction Reaction • The gain of electrons by a substance in a chemical reaction • Which substances were reduced during photosynthesis?

18. StomaThis opening how plants exchange gases! Why are the stomata located on the bottom of leaves?

19. Stoma • Stoma Open • CO2 can increase • O2 will decrease and leave cells • Stoma Closed • CO2 decrease • O2 increases

20. C4 Pathway • Plants that use this are called C4 plants and have stomata closed during hot part of day • Enzyme fixes CO2 to a 4-carbon compound when CO2 is low and O2 is high • Corn, sugar cane, & crab grass • Usually tropical climates

21. CAM Pathway • Water conserving pathway • Hot dry climates • Stoma closed during day & open at night • Opposite of ordinary plants • Pineapples & cactuses

22. CAM Pathway • During the day • Stoma are closed • CO2 is released from compounds and enters Calvin cycle • During the night • Stoma are open • Take in CO2 and fix into carbon compounds

23. PHOTOSYNTHESIS • What affects photosynthesis? • Light intensity: as light increases, rate of photosynthesis increases

24. PHOTOSYNTHESIS • What affects photosynthesis? • Carbon Dioxide: As CO2 increases, rate of photosynthesis increases

25. PHOTOSYNTHESIS • What affects photosynthesis? • Temperature: • Temperature Low = Rate of photosynthesis low • Temperature Increases = Rate of photosynthesis increases • If temperature too hot, rate drops