The Calvin Cycle “The Dark Reactions”

1. The Calvin Cycle“The Dark Reactions” Packet #33 Chapter #10

2. Introduction • The Calvin Cycle occurs in the stroma of the chloroplast and involves the usage of CO2, NADPH and ATP to make sugar.

3. Introduction II • The Calvin Cycle has multiple steps that fall under three broad phases. • Carbon Fixation • Reduction • Regeneration of CO2 Acceptor. • Each phase involves the use of one or more enzymes. • However, only a select few will be mentioned in the packet.

4. Introduction IIICalvin Cycle Phases • Carbon Fixation • Use of carbon dioxide • Reduction • 1, 3 bisphosphoglycerate is reduced to the sugar G3P • 6 ATP’s is used • Reduced using the electrons produced by the oxidation of NADPH • Regeneration of CO2 Acceptor • This acceptor, RuBP, is then re-used in carbon fixation to continue the next cycle of the Calvin Cycle

5. Carbon Fixation

6. Carbon Fixation I • Carbon fixation begins with three molecules of ribulose-1,5-bisphosphate (RuBP). • Each RuBP contains 5 carbons.

7. Carbon Fixation II • The enzyme, ribulose bisphosphate carboxylase (rubisco), converts EACH molecule of RuBP into TWO molecules of 3-phosphoglycerates. • Rubisco is the ONLY enzyme used during carbon fixation and the process requires 5 steps.

8. Carbon Fixation III • Rubisco adds CO2 to EACH RuBP to produce a 6-carbon intermediate known as β-Keto acid.

9. Carbon Fixation III • Each β-Keto acid is split to produce two molecules of 3-phosphoglycerate.

10. Carbon Fixation IV • The formation of 3-phosphoglycerate includes the making of a 6-carbon intermediate known as β-Keto acid.

11. Carbon Fixation V • At the end of carbon fixation three molecules of RuBP will have been converted into six molecules of 3-phosphoglycerate via the enzyme rubisco.

12. Reduction

13. Reduction I • The phase begins with six molecules of 3-phosphoglycerate.

14. Reduction II • The enzyme phosphoglycerate kinase adds a phosphate to each 3-phosphoglycerate to produce 1,3-bisphosphoglycerate. • There should be a total of six molecules of 1,3-bisphosphoglycerate at the end of this step.

15. Reduction III • The enzyme phosphoglycerate kinase adds a phosphate to each 3-phosphoglycerate to produce 1,3-bisphosphoglycerate. • There should be a total of six molecules of 1,3-bisphosphoglycerate at the end of this step.

16. Reduction IV • The enzyme glyceraldehyde-3-phosphate dehydrogenasereduces each 1,3-bisphosphoglycerate to glyceraldehye-3-phosphate. • There should be a total of six molecules of glyceraldehyde-3-phosphate at the end of this step. • The electrons necessary for this step are extracted from NADPH.

17. Reduction V • One of the G3P’s are extracted from the cycle and await the cycle to repeat to produce another “extracted” G3P. • The two extracted G3P’s combine to make one glucose molecule.

18. Reduction VI • After the extraction of one of the G3P’s, the remaining five enter the final phase of the Calvin Cycle.

19. Regeneration of the CO2Acceptor (RuBP)

20. Regeneration of RuBP I • Through a series of complex steps, three molecules of RuBP are produced from five molecules of G3P.

21. Regeneration of RuBP II • The complicated steps in the re-production of RuBP.

22. Regeneration of RuBP III • The final step in the regeneration of RuBP requires the use of the enzyme phosphoribulokinase. • Phosphoribulokinase converts Ribulose-5-phosphate (Ru5P) into Ribulose-1, 5-bisphosphate. (RuBP) • Three molecules of RuBP will be produced from the five molecules of G3P.

23. Review

24. Review—The Big Picture

25. Calvin Cycle—Overall Inputs & Outputs • Inputs • CO2 • H2O • ATP • NADPH • Outputs • Sugars (Glucose) • ADP • P • NADP+