Light-Independent Reactions

Calvin Cycle

• CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast.
• The CO2 then combines with a 5-carbon compound called ribulose biphosphate (RuBP).
• This reaction is catalysed by an enzyme called ribulose biphosphate carboxylase (RuBISCO).
• The 6-carbon compound formed is unstable and quickly breaks down into 2 molecules of a 3-carbon compound called glycerate 3-phosphate (GP).
• Now ATP, from the light-dependent reactions, provides the energy to reduce GP to a 3-carbon sugar phosphate called glyceraldehyde 3-phosphate (GALP).
• This reduction reaction also requires H ions, which come from the reduced NADP, also from the light-dependent reactions.
• The reduced NADP is then recycled to NADP.
• 2 out of every 12 GALPs formed are involved in the creation of a 6-carbon sugar which can be converted into other organic compounds, such as, amino acids.
• 10 out of every 12 GALPs are used to regenerate RuBP.
• The 10 GALP molecules rearrange to form 6 5-carbon compounds.
• Then, using the last of the ATP, phosphorylation takes place to form RuBP.

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