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The Light Independent Reaction

The Light Independent Reaction. Light Independent Rxn. Occurs in stroma of chloroplast Referred to as ‘Calvin cycle’ raw materials are CO 2 -obtained from the atmosphere by diffusion through the stomata, ATP and NADPH both obtained from the light dependent stage

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The Light Independent Reaction

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  1. The Light Independent Reaction

  2. Light Independent Rxn • Occurs in stromaof chloroplast • Referred to as ‘Calvin cycle’ • raw materials are CO2-obtained from the atmosphere by diffusion through the stomata, ATP and NADPH both obtained from the light dependent stage • produces organic compounds such as glucose, sucrose, amino acids, fatty acids and glycerol (building block of other carbohydrates and plant oils)

  3. Light Independent Rxn • CO2 converted to carbohydrate • Does not require light (dark rxn)

  4. Light Independent Rxn • Occurs in a cycle of 4 processes: • Carboxylation-CO2 fixation • Reduction of glycerate-3-phosphate (G-3-P) • Regeneration of ribulosebisphosphate (RuBP) • Product synthesis-metabolism of TP to carb, a.a., lipids

  5. CO2 FIXATION • CO2 is combined with a 5-carbon (pentose) sugar called ribulosebisphosphate (RuBP) in the presence of Rubisco • involves one of the most abundant enzyme in nature-ribulosebisphosphate carboxylase, RuBP carboxylase or Rubisco • RuBP-CO2 acceptor • Addition of CO2-carboxylation

  6. CO2 FIXATION • produces an unstabe 6C short-lived intermediate temporarily attached to Rubisco • As Rubiscoreleases the intermediate it immediately disintegrates into 2 molecules of a 3C compound called glycerate-3-phosphate (G-3-P) • First product of photosynthesis

  7. CO2 FIXATION • RuBP + CO2 + H2O Rubisco 2GP (5C sugar) (3C acid)

  8. REDUCTION ATP ADP + Pi • GP TP (3C acid) NADPH+H NADP+ H2O (3C sugar) GP-glycerate phosphate is a 3C acid, contains a carboxyl gp-COOH (acidic) TP-triose phosphate is a 3C sugar, conains an aldehyde gp-CHO with a phosphate gp attached. Contains more chemical energy than GP

  9. REDUCTION OF (G-3-P) • involves the conversion of G-3-P to a triose phosphate (TP) by a reduction reaction in the presence of ATP and NADPH • TP is the first carbohydrate made in photosynthesis • ATP provides the energy for the reaction and NADPH provides the hydrogen for the reduction reaction

  10. REDUCTION • Reducing power of reduced NADP and energy from ATP used to remove O from GP (reduction) • Rxn takes place in 2 stages • Using some of the ATP produced in light deprxn • Using ALL the reduced NADP

  11. REGENERATION OF RIBULOSE BISPHOSPHATE (RuBP) • 5/6 of the total TP produced is used to regenerate the starting RuBPmolecule • Remaining ATP used to convert RuP to RuBP • NB- 6 mol CO2 used to make 2 mol of TP (3C sugar)

  12. PRODUCT SYNTHESIS • TP does not accumulate-immediately converted to glucose phosphate, glucose • Sugar translocated as sucrose-disacch • Glucose phosphates starch- stored in stems, roots • Glycerol + fatty acids lipids-glycerol formed from TP, fatty acids from the accumulation of acetyl coenzyme A

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