5.4—Light-independent reactions and Calvin cycle products

In the light-independent reactions, rubisco combines carbon dioxide with RuBP. The unstable six-carbon product splits into GP; ATP and reduced NADP reduce GP to GALP, and most GALP is used with ATP to regenerate RuBP.

Carbon fixation moves carbon dioxide into an organic molecule. Some GALP leaves the cycle to form glucose and other molecules; the rest keeps the cycle running, so the carbon input and regeneration steps are linked.

For each turn, one carbon dioxide is fixed and only a fraction of a glucose molecule is produced; six turns are needed for one six-carbon glucose, while five-sixths of GALP is recycled to RuBP.

The light-independent reactions do not use light directly, but they depend on ATP and reduced NADP from the light-dependent reactions. GP, GALP and RuBP are different intermediates, not interchangeable names.