The Calvin Cycle

1. The Calvin Cycle Photosynthesis

2. The Big Picture • The Calvin cycle • Occurs in the stroma • Cyclic: ‘final’ product is the ‘initial’ reactant • Details determined by Melvin Calvin, 1960. He received the Nobel Prize in 1961. • Can be divided into three phases • Carbon fixation • Reduction Reactions • Ribulose 1,5-bisphosphate (RuBP) regeneration

4. Phase 1: Carbon Fixation • The Calvin cycle is also known as C3 photosynthesis. • Most plants are C3 plants. • Reaction catalyzed by the enzyme: • RIBULOSE BISPHOSPHATE CARBOXYLASE/OXYGENASE • (RUBISCO) • enzyme works very slowly • typical plant enzymes process 1000 molecules/s. • rubisco: 3 molecules/s. • rubisco makes up about ½ all protein in a typical leaf  • MOST ABUNDANT PROTEIN ON EARTH! • 3CO2 + 3 ribulose 1,5-bisphosphate (RuBP) (5C)  3 unstable 6C intermediates • 3 6C splits into 6 ____ molecules: PGA INITIAL REACTANT(S) __________________ FINAL PRODUCT(S):____________________ ATP USED: ________________________ NADPH USED: ______________________

5. Phase 2: Reduction Reactions • Each of the 6 3C PGA molecules is phosphorylated by an ATP to form ___ molecules of 1,3-BPG. • Each 1,3-BPG reduced to glyceraldehyde 3-phosphate, G3P. • 6 NADPH  6 NADP+ + 6 Pi • 1 molecule of G3P exits the cycle as a final product. INITIAL REACTANT(S) __________________ FINAL PRODUCT(S):____________________ ATP USED: ____________________________ NADPH USED: ________________________

6. Phase 3: RuBP Regeneration • 5 G3P (___C)  3 RuBP (__ C) • Series of enzyme-catalyzed reactions. • RuBP becomes a ‘reactant’ of the process. INITIAL REACTANT(S) __________________ FINAL PRODUCT(S):____________________ ATP USED: ____________________________ NADPH USED: ________________________

7. Why is the Calvin cycle x 3? • 3 CO2 used at first. • Three CO2 molecules must be fixed before one 3C molecule of G3P can be removed. • Why?: need to maintain pool of intermediate molecules to sustain the cycle. • 6 ‘turns’ of cycle fix enough to produce the equivalent of 1 glucose.

8. Overall Reaction: For the NETsynthesis of ONE G3P molecule ___ ATP ___ NADPH are used. These molecules come from: ______________________. G3P will become: _______________ _______________ _______________ Which will be used in: _______________________

9. The Importance of G3P (1) • When is that made, again? • Recall that 6 G3P are formed during the reduction reactions of the Calvin cycle (Phase 2) • One of the 6 G3P molecules is used to make glucose, starch, or sucrose... used in ____________________. • G3P can be stored (as one of the former molecules) or act as a reactant in the Calvin cycle.

10. Questions • How many ‘turns’ of the Calvin cycle does it take to produce ONE G3P molecule? • How many carbons does one G3P molecule contain? • How many carbons does one glucose molecule contain? • How many G3P molecules are needed to produce one glucose molecule? • How many turns of the Calvin cycle are required to produce one glucose?

11. The Importance of G3P (II) • Higher plants generally fix more CO2 into sugars than they require for immediate energy needs. • When conditions are optimal, and photosynthesis produces more glucose molecules than needed  glucose is polymerized into amylose and amylopectin  starch granules within chloroplasts. • Which environmental conditions will cause ‘plants’ to store this starch? _____________________________________________________________________________ • Which environmental conditions will cause ‘plants’ to use G3P immediately? _____________________ • ______________________________________.

12. Possible Paths of G3P

13. Plants.... • Possess many nonphotosynthetic tissues • Roots • Some stems • Some flowers • These tissues need energy to meet their needs. • So how do they function? • Plants have a ‘circulatory system’ just like we do. • Xylem vessels move water and nutrients from the root to the stoma (via __________________) • Phloem moves glucose (made by the ________) around the plant.

14. Homework/Seatwork • Page 166 # 9, 10, 11