RuBP stands for ribulose bisphosphate.
RuBP is a crucial five-carbon molecule involved in the Calvin cycle, a key part of photosynthesis. Specifically, it functions as the initial carbon dioxide acceptor. In the Calvin cycle, carbon dioxide from the atmosphere is combined with RuBP through the action of the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase). This carboxylation process results in an unstable six-carbon molecule, which immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA). 3-PGA is then converted into glyceraldehyde-3-phosphate (G3P), which serves as the precursor for glucose and other organic molecules. Crucially, the Calvin cycle includes a regeneration phase where RuBP is regenerated from G3P, allowing the cycle to continue and fix more carbon dioxide. Without RuBP regeneration, carbon fixation would halt.
