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Photosynthesis

Photosynthesis. Alternative Mechanisms of Carbon Fixation. RuBisCO Image from: http://www.ncbi.nlm.nih.gov/books/NBK22344/. RuBisCO is the most abundant protein on Earth. It catalyzes the first reaction of the Calvin cycle.

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Photosynthesis

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  1. Photosynthesis Alternative Mechanisms of Carbon Fixation

  2. RuBisCOImage from: http://www.ncbi.nlm.nih.gov/books/NBK22344/ • RuBisCO is the most abundant protein on Earth. • It catalyzes the first reaction of the Calvin cycle.

  3. PhotorespirationImage from: http://access.mmhs.ca/docs/Science/MMHS%20Web%20folder/Kamla/20102008.htm • In the first reaction of the Calvin cycle, CO2 is “fixed”, forming 2 molecules of 3-PGA. • O2 competes with CO2 for the active site of RuBisCO.

  4. PhotorespirationImage from: http://access.mmhs.ca/docs/Science/MMHS%20Web%20folder/Kamla/20102008.htm • When RuBP is oxidized, it produces only 1 molecule of 3-PGA. • This process is called photorespiration.

  5. Photorespiration • In warmer temperatures, RuBisCO’s affinity for O2 increases, resulting in less CO2 being fixed into G3P. • How have plants in warmer climates evolved to cope with RuBisCO’s affinity for O2?

  6. C4 PhotosynthesisImage from: http://hyperphysics.phy-astr.gsu.edu/hbase/biology/calvin.html • CO2 is combined with PEP to form 4-carbon oxaloacetate (enzyme PEP carboxylase) in mesophyll cells • oxaloacetate is converted to malate, then transported into bundle-sheath cells • malate is decarboxylated forming pyruvate, and CO2 enters the Calvin cycle

  7. C4 PhotosynthesisImage from: http://hyperphysics.phy-astr.gsu.edu/hbase/biology/calvin.html

  8. C4 PhotosynthesisImage from: http://www.botany.hawaii.edu/faculty/webb/bot311/bot311-00/psyn/PsynDark2.htm

  9. C4 Plants

  10. CAM Plants • crassulacean acid metabolism (CAM), first discovered in Crassulacea family of plants • stomata are closed during the day, so CO2 is only absorbed at night • C4 pathway at night, C3 pathway during the day

  11. CAM PlantsImage from: http://hyperphysics.phy-astr.gsu.edu/hbase/biology/calvin.html

  12. CAM plants

  13. Animation Narrated animation of C4 photosynthesis and CAM plants: http://www.uic.edu/classes/bios/bios100/lectures/c4.htm

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