AP Bio Ch. 10 Calvin cycle

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AP Bio Ch. 10 Calvin cycle

  1. 1. Photosynthesis The Calvin Cycle Melvin Calvin
  2. 2. It’s a cycle • Like a sugar factory in the cell • Starting molecule regenerated “Roo Bee Pee”
  3. 3. Comparison of Citric Acid Cycle and Calvin Cycle Cell Respiration Citric acid cycle is catabolic oxidizes glucose and releases energy Photosynthesis Calvin cycle is anabolic - building sugar and consuming energy
  4. 4. General Overview • In Calvin cycle - CO2 enters, 3-C sugar exits • Cycle uses ATP for energy and uses NADPH as a reducing agent to add electrons to make the sugar – The ATP and NADPH come from the Light Reactions
  5. 5. Quick Think • With someone near you, discuss how the light reactions support the dark reactions (aka the Calvin Cycle) • Be prepared to share your discussion
  6. 6. • Calvin cycle makes a 3-carbon sugar called G3P (glyceraldehyde-3phosphate)
  7. 7. Calvin Cycle - 3 phases + regeneration of starting molecule Input Three CO2 1 Three RuBP Six 3-PGA Six 4 Three ADP Six ADP + Six Calvin cycle Three 2 Six Six NADP+ Six G3P Five G3P 3 One G3P Glucose and other compounds Output
  8. 8. Phase 1- Carbon Fixation • 3 CO2 molecules enter Calvin Cycle 1 at a time • Each one is attached to a 5-C sugar ribulose biphosphate (RuBP) • Enzyme rubisco (RuBP carboxylase) catalyzes this reaction – Rubisco is likely the most abundant protein on earth • Product of this phase is a 6-C highly unstable molecule that immediately splits in 1/2 to make 2 molecules of 3The product phosphoglycerate for of Phase 1, CO2 that each entered (so 6 total) 6 made
  9. 9. Go to your diagrams
  10. 10. Quick Think • With someone near you, summarize what happens in the first phase of the Calvin Cycle • Be prepared to share
  11. 11. Phase 2 - Reduction 1. Each 3phosphogylcerate gets an extra phosphate group from ATP to become 1,3biphosphoglycerate 6 made, takes 6 ATP to do this
  12. 12. Phase 2 - Reduction 2. A pair of electrons donated by NADPH reduces 1,3biphosphoglycerate to G3P - the electrons from NADPH reduce the carboxyl group of 3-phosphoglycerate to the aldehyde group of G3P, which stores more potential energy
  13. 13. Phase 2 - Reduction • For every 3 molecules of CO2 that enter the cycle, 6 molecules of G3P are formed • Only 1 counts as a net gain because the other 5 must recycled back to RuBP to allow the cycle to continue Go to your diagrams
  14. 14. Quick Think • With someone near you, summarize what happens in the 1st AND 2nd phases of the Calvin Cycle • Be prepared to share
  15. 15. Phase 3 - Regeneration of the CO2 acceptor (RuBP) • The 5 G3Ps are rearranged into 3 molecules of RuBP • Requires 3 ATP to do this • RuBP can now continue cycle and accept new CO2s that enter
  16. 16. Go to your diagrams
  17. 17. Quick Think • With someone near you, summarize all 3 phases of the Calvin cycle • Be prepared to share
  18. 18. Calvin Cycle Summary • Net - 1 G3P sugar • Consumed - 9 ATP, 6 NADPH • G3P that exits the cycle becomes the starting molecule in various metabolic pathways that make different organic compounds including glucose
  19. 19. Calvin Cycle Summary • To make 1 molecule of glucose, the Calvin cycle uses 6 molecules of CO2, 18 molecules of ATP, 12 molecules of NADPH
  20. 20. Quick Think • With someone near you, discuss why it is called the Calvin CYCLE • Be prepared to share
  21. 21. That’s a lot of ATP… • It take a lot of ATP to make glucose, but it is worth it because glucose stores so much potential energy for the cell
  22. 22. Connections between the Light Reactions and the Calvin Cycle • Light reactions produce ATP and NADPH, which are used during the Calvin Cycle • Calvin cycle returns ADP and NADP+ to the chloroplast, so they can be used again in the Light Reactions
  23. 23. Quick Think • With someone near you, discuss how the light reactions and the Calvin cycle support each other • Be prepared to share
  24. 24. 1. • What is the overall chemical equation for photosynthesis?
  25. 25. 2. • What molecule goes in to the Calvin Cycle?
  26. 26. 3. • What molecule comes out of the Calvin cycle?
  27. 27. 4. Bonus • What is the name of the enzyme that fixes carbon dioxide?
  28. 28. 5. Bonus • How many sugar molecules leave the Calvin Cycle?

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