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Light Independent Reactions

Light Independent Reactions. Occurs in the stroma and converts carbon dioxide to carbohydrates using energy from ATP and NADPH CO 2 must be converted to organic compounds (this is called CO 2 assimilation) – this is done in the light independent reaction. Carbon Fixation.

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Light Independent Reactions

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  1. Light Independent Reactions • Occurs in the stroma and converts carbon dioxide to carbohydrates using energy from ATP and NADPH • CO2 must be converted to organic compounds (this is called CO2 assimilation) – this is done in the • light independent reaction Carbon Fixation Regeneration of RuBP Reduction Ribulose 1,5-bisphosphate

  2. 1. Carbon Fixation CO2 + RuBP unstable C6  2 PGA • CO2 bonds to a pre-existing molecule in the stroma (Ribulose 1,5-bisphosphate… aka RuBP) • The resulting 6 carbon intermediate quickly changes to 2 three-carbon molecules of 3-phosphoglycerate (PGA) • This is catalyzed by Ribulosebisphosphatecarboxylase (Rubisco) - possibly the most abundant protein on earth

  3. 2. Reduction • The new PGA is phosphorlated by ATP and then reduced by NADPH creating Glyceraldehyde-3-phosphate • Some G3P goes on to make glucose and other carbohydrates • Most G3P goes on to replenish RuBP

  4. 3. Regenerating RuBP Energy, supplied by ATP is required to break and reform bonds to make the 5 carbon RuBP The Calvin cycle must be completed 6 times in order to synthesize one molecule of glucose. Of 12 G3P molecules that are produced in 6 cycles 10 are used for regeneration of RuBP, and 2 are used to produce one glucose molecule. Net equation is : 6 CO2 + 18 ATP + 12 NADPH + water  3 G3P + 16 Pi + 18 ADP + 12 NADP+

  5. Glyceraldehyde-3-phosphate Is used to produce: Glucose Sucrose Cellulose Oils AAs (along with nitrogen)

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