III. Light Dependent Reactions

1. I. Anatomy of Photosynthesis II. How plants harness sunlight III. Light Dependent Reactions A. Photo-oxidation of Chlorophyll B. Chemiosmotic model of ATP production. IV. Light Independent Reactions A. Calvin Cycle

3. Non-cyclicPhotophosphorylation + charge pH = 4 - charge pH = 8

4. Cyclic photophosphorylation Make extra ATP

5. Turn to your neighbor and… Graph changes in pH of the thylakoid interior over one 24 hr period. Indicate when ATP production during the light reactions is zero. Night Day Night 14 9 No ATP No ATP pH 7 4 1 6AM 6 PM

6. The Big Picture What have we produced so far? ATP NADPH CO2 provides the carbon and oxygen provides high energy electron and H+ ions provides the energy Used to make energy rich sugar molecules during the light independent reactions!

7. The Calvin Cycle

8. CARBON FIXATION (3) CO2 molecules enter Rubisco attaches the CO2 to RuBP

9. REDUCTION 6 ATP and 6 NADPH used 1 G3P molecule produced

10. Regenerate RuBP Use 3 more ATP

11. And boy can plants fix carbon!

12. What do plants do with the sugars they make? Fuel cellular respiration most!

13. Similarities between photosynthesis and cellular respiration… Chemiosmosis Energy Coupling Examples

14. Differences between cellular respiration and photosynthesis. Cellular Respiration In CR electron carriers bring electrons to the ETC, and O2 finally accepts them and is reduced to H2O. Photosynthesis In photosynthesis H2O brings electrons to the ETC and becomes O2, an electron carrier finally accepts the electrons.

15. Differences between cellular respiration and photosynthesis. During the Calvin cycle, CO2 is being reduced into sugar CO2 During the Krebs cycle, sugars are oxidized and become CO2

16. Photosynthetic Adaptations What problems may a plant experience when it is exposed to arid (dry) conditions? Dehydration Response Close stomata to prevent dehydration Elevated O2 levels in the leaves

17. Rubisco – an enzyme that catalyzes the addition of CO2 to RuBP. Photorespiration O2 competes with CO2 for the active site on Rubisco. Photorespiration Calvin cycle sometimes called the C3 pathway

18. Rubisco P G A P G A RuBp CO2 Later becomes glucose! Rubisco P G A RuBp O2 Photorespiration – these CO2’s did not get incorporated into glucose this time! CO2 CO2

19. Photorespiration can lead to lower photosynthetic output by siphoning carbon from the Calvin cycle! They produce less sugar!!!

20. Turn to your neighbor and discuss the following questions… 1) What factor determines which reaction below occurs more often? • The concentration of rubisco • The relative concentration of CO2 and O2 • The concentration of RuBp Competing reactions CO2 2) This is most similar to which of the mechanisms of enzyme regulation we discussed earlier in the semester? rubisco 2 molecules of 3-phosphoglycerate CO2 + RuBP

21. Adaptations to arid climates A) C4 plants - spatial separation of steps B) CAM plants - temporal separation of steps

22. Leaf anatomy of plants adapted for hot/arid conditions (C4 plants)… O2 C4 pathway C3 pathway Separate CO2 fixation and sugar making into two different cells

23. CO2 CO2 Calvin Cycle sugar CAM Plants - steps performed at different times • Desert plants…cacti, succulent plants, pineapples… Organic acid • Close their stomata during the day to minimize water loss, and open stomata at night. • At night they store CO2 in organic acids. • CO2 is released from organic acids in the day and used in the Calvin cycle.

24. The Silversword