Biochemistry Questions Biochemistry Questions / Explain the three stages of the Calvin cycle and their respective inputs and outputs.

  1. Carboxylation Carboxylation is catalysed by rubisco, the most abundant protein (and subsequently enzyme) on Earth, converting ribulose-1,5-bisphophate to 3-phosphoglycerate.

  2. Reduction Reduction uses ATP and NADPH from the light reactions, converting 3-phosphoglycerate to 1,3-bisphosphoglycerate (with the enzyme 3-phosphoglycerate kinase). 1,3-bisphosphoglycerate is then converted to glyceraldehyde-3-phosphoglycerate, using glyceraldehyde-3-phosphoglycerate dehydrogenase.

  3. Regeneration Glyceraldehyde-3-phosphoglycerate is regenerated into ribulose-1,5-bisphosphate, via the intermediate ribulose-5-phosphate. Using phosphoribulose kinase and ATP, anther phosphate group is added to form the starting material, glyceraldehyde-3-phosphoglycerate.

The output of the Calvin cycle is one molecule of glyceraldehyde-3-phosphoglycerate. The other five molecules of GAP produced are used in the regeneration process, allowing the reaction to continue. CO2, ATP, and NADPH are inputs, providing phosphates, carbons, and reducing power (NADPH).