CO2 Fixation To Synthesize Macromolecules

CO2 fixation is a process in which inorganic carbon is converted into organic carbon that can be used in other pathways to synthesize macromolecules. The Calvin-Benson-Bassham (CBB) pathway is often utilize by photoautotroph, photoheterotroph, and lithoautotroph for CO2 fixation. The CBB pathway is a cyclic pathway that occurs in 3 stages, the carboxylation phase, follow by the reduction phase, and then the regeneration phase. In the carboxylation phase, a 5 carbons compound called ribulose 1,5-bisphosphate accept a CO2 compound, forming an unstable 6 carbons compound intermediate. The 6 carbons intermediate is then splits into two 3 carbons compounds called 3-phosphoglycerate. The 3-phosphoglycerate compounds enter the reductive phase where the compounds get phosphorylated to form 1,3-bisphosphoglycerate by hydrolyzing ATP molecules. …show more content…
When 1,3-bisphosphoglycerate get reduced, one of the phosphates get split off and 1,3-bisphosphoglycerate is convert to glyceraldehyde 3-bisphosphate, which can then enter glycolysis as a precursor metabolite. In the regeneration phase, some of the glyceraldehyde 3-bisphosphate that was form can be used to convert back to ribulose 5-phosphate through a series of reactions. Ribulose 5-phosphate then get phosphorylated by hydrolysis of another ATP molecule to form ribulose 1,5-bisphosphate, which can return back to the carboxylation phase and go through another cycle of the CBB pathway. The reverse citric acid cycle is another pathway that can be used for carbon fixation that is utilize by lithoautotroph bacteria and