3PGA

3PGA refers to 3-phosphoglycerate, a crucial molecule in both photosynthesis and cellular respiration. In photosynthesis, 3PGA is an intermediate in the Calvin cycle, the light-independent reactions that convert carbon dioxide into sugars. Specifically, it is formed when RuBisCO, the enzyme responsible for carbon fixation, catalyzes the reaction between ribulose-1,5-bisphosphate (RuBP) and carbon dioxide. This initial three-carbon compound is then reduced and rearranged to form glyceraldehyde-3-phosphate (G3P), which can be used to synthesize glucose and regenerate RuBP.

In cellular respiration, 3PGA is also a key intermediate, but in the process of glycolysis. Here, it is generated from 1,3-bisphosphoglycerate through the action of phosphoglycerate kinase, which also produces ATP. Subsequently, 3PGA is converted to 2-phosphoglycerate, leading to the formation of phosphoenolpyruvate (PEP) and a second molecule of ATP in the final steps of glycolysis. The interconversion of 3PGA between these two major metabolic pathways highlights its central role in energy metabolism for many organisms.