Light independent reactions of photosynthesis


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Light independent reactions of photosynthesis

  1. 1. Light Independent Reactions of Photosynthesis Dr. Mark A. McGinley Honors College and Department of Biological Sciences Texas Tech University
  2. 2. Results of the Light Dependent Reactions• The potential energy in the ATP and NADPH produced during the light dependent reactions of photosynthesis can only be stored for a fraction of a second – Thus this energy must be used immediately or the energy will be lost
  3. 3. Calvin Cycle• The Calvin Cycle is the chemical process that helps to convert potential energy from ATP and NADPH into potential energy stored in glucose• The Calvin Cycle occurs in the stroma
  4. 4. Calvin Cycle First Reaction C02 reacts with RUBP to form unstable 6 Cintermediate
  5. 5. Where Does the CO2 Come From?• The CO2 comes from the environment – Terrestrial plants pick up CO2 from the air – Marine and aquatic plants pick up CO2 from the water
  6. 6. RuBP Carboxylase• The reaction of CO2 + RUBP is calatlyzed by the enzyme RuBP carboxylase – rubisco
  7. 7. RuBP Carboxylase• The most abundant protein on the planet – More than50% of protein in some plant cells – 40 million Kg of RuBP carboxlyase created each year • 1000 Kg per second!!
  8. 8. RuBP Carboxylase• Protein with quaternary structure – 8 large subunits – 8 small subunits• Large subunits coded for by chloroplast DNA• Small subunits coded for by nuclear DNA
  9. 9. Calvin CycleCO2 + RuBP => unstable 6 carbon intermediate 2 molecules of PGA (3 phosphoglycerate)
  10. 10. Calvin Cycle
  11. 11. Calvin Cycle Important Points• Converting PGA to Glyceraldehyde phosphate (G3P) requires the addition of energy released by ATP and NADPH – (this is the same ATP and NADPH that were just produced in the Light Dependent Reactions)
  12. 12. Calvin Cycle Important Points• Glyceraldehyde 3 Phospate (G3P) – Can be used to produced glucose • Potential energy stored in chemical bonds of glucose – Can be used to make RUBP • Converting G3P to RUBP requires the input of energy from ATP (also created by the light dependent reactions)
  13. 13. Light Independent Reactions• Please don’t call these the “Dark Reactions” (you will sometimes see this term, but try to avoid it) – Light independent reactions must take place in the light because light is required to put potential energy in the bonds of ATP and NADPH
  14. 14. Light Independent Reactions• Potential energy in ATP and NADPH is converted to potential energy held in glucose• CO2 => => glucose