calvin cycle

• RuBP (ribulose bisphosphate) combines with CO2 to form an unstable molecule called RuBP carboxylase/oxygenase (rubisco).
• Sedoheptulose-1,7-bisphosphatase is an enzyme that plays a crucial role in the regeneration phase of the Calvin Cycle.
• In the Calvin Cycle, carbon dioxide enters the chloroplast through diffusion or active transport.
• Phosphoglycerate kinase is an enzyme that helps convert 3-phosphoglycerate into 1,3-bisphosphoglycerate during the Calvin Cycle.
• The Calvin Cycle is also known as the light-independent reactions.
• Rubisco is the most abundant enzyme involved in the Calvin Cycle, responsible for carbon fixation.
• Carbon dioxide enters the chloroplast through stomata, which are small openings on the surface of leaves that allow gases to enter and exit.
• The Calvin Cycle is also known as the light-independent reactions or dark reaction.
• Rubisco (ribulose bisphosphate carboxylase/oxygenase) is an enzyme involved in carbon fixation during photosynthesis.
• The first step involves the activation of ribulose bisphosphate by ATP, forming an activated intermediate known as phosphoribulopyrophosphate (PRPP).
• The Calvin Cycle involves three phases: Carbon Fixation Phase, Reduction Phase, and Regeneration Phase.
• This reaction requires energy from ATP and is catalyzed by PRPP synthase.
• Phosphoribulopyrophosphate reacts with CO2 to produce two molecules of 3-phosphoglycerate, which are then converted into glyceraldehyde-3-phosphate (GAP) via several steps involving various enzymes such as rubisco, sedoheptulose-1,7-bisphosphatase, triose phosphate isomerase, and aldolase.
• In the second step, CO2 combines with PRPP to form unstable molecules called two-carbon compounds.
• The Calvin Cycle occurs in the stroma of chloroplasts.
• Glyceraldehyde-3-phosphate dehydrogenase is an enzyme involved in converting glyceraldehyde-3-phosphate into 1,3-bisphosphoglycerate during the Calvin Cycle.
• The Calvin Cycle involves three stages: Carboxylation, Reduction, and Regeneration.
• Carbon fixation occurs when carbon dioxide reacts with ribulose bisphosphate (RuBP), forming two molecules of 3-phosphoglyceric acid.
• Fructose-6-phosphate is produced from sedoheptulose-1,7-bisphosphate by fructose-6-phosphate phosphomutase.
• ATP is used to convert one of these intermediates into another compound called RuBP, completing the cycle.
• Fructose-6-phosphate is produced from sedoheptulose-1,7-bisphosphate by fructose-6-phosphate phosphomutase during the Calvin Cycle.
• Carbon fixation occurs when ribulose bisphosphate reacts with carbon dioxide to produce two molecules of phosphoglyceric acid.
• Reduction phase: ATP and NADPH are used to reduce the phosphoglyceric acid to glyceraldehyde-3-phosphate.
• Glyceraldehyde-3-phosphate dehydrogenase catalyzes the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.
• These two-carbon compounds undergo hydrolysis to produce three-carbon sugar intermediates called 3-phosphoglycerate.
• Light energy absorbed by photosystem II drives the electron transport chain, producing ATP and reducing power in the form of NADPH.
• Photorespiration is an alternative pathway that competes with the Calvin cycle for resources such as ATP and NADPH.
• RuBP carboxylase/oxygenase (rubisco) enzyme plays a crucial role in both carbon fixation and photorespiration.
• Calvin cycle


  The second stage of photosynthesis where carbon dioxide is fixed into organic molecules
• Calvin cycle reactions


  1. Carbon fixation

  2. Reduction

  3. Regeneration of the starting molecule
• Calvin cycle


  • Takes place in the stroma of chloroplasts
  • Fueled by ATP and NADPH from the light reactions
• Carbon fixation


  1. CO2 combines with RuBP (a 5-carbon acceptor molecule)

  2. Produces two 3-phosphoglycerate (3-PGA) molecules

  3. Catalyzed by the enzyme rubisco
• Reduction


  1. 3-PGA molecules gain a phosphate group from ATP

  2. 3-PGA molecules are reduced by NADPH to form glyceraldehyde 3-phosphate (G3P)

  3. Releases NADP+ and inorganic phosphate
• Regeneration


  1. One G3P molecule exits the cycle to make glucose

  2. Five G3P molecules are recycled to regenerate three RuBP molecules

  3. Requires ATP
• For every three turns of the Calvin cycle, three CO2 molecules are fixed, producing six G3P molecules, of which one exits the cycle and five are recycled
• It takes six turns of the Calvin cycle, using 18 ATP and 12 NADPH, to produce one glucose molecule
• Plants move

  • Morning glories and Venus flytraps move
  • Some plants have reflexive movement in response to being touched
• If a plant is in drought conditions

  Chloroplast activity slows down
• Wilting occurs because the plant is undergoing plasmolysis which reduces the turgor pressure on the plant's cell wall
• Calvin Cycle


  3 CO2 + 6 NADPH + 6 H+ + 9 ATP + 5 H2O → glyceraldehyde-3-phosphate (G3P) + 6 NADP+ + 9 ADP + 8 Pi