of NADH themselves go on to produce approximately 3 molecules of ATP each. In the Calvin cycle 1,3-BPG has a very similar role in the Calvin cycle to its role in the glycolytic pathway. For this reason both reactions are said to be analogous. However the reaction pathway is effectively reversed. The only other major difference between the two reactions is that NADPH is used as an electron donor in the calvin cycle whilst NAD+ is used as an electron acceptor in glycolysis. In this reaction cycle 1,3BPG originates from 3-phosphoglycerate and is made into glyceraldehyde 3-phosphate by the action of specific enzymes. Contrary to the similar reactions of the glycolytic pathway, 1,3BPG in the Calvin cycle does not produce ATP but instead uses it. For this reason it can be considered to be an irreversible and committed step in the cycle. The outcome of this section of the cycle is an inorganic phosphate is removed from 1,3BPG as a hydrogen ion and two electrons are added to the compound+. In complete reverse of the glycolytic pathway reaction, the enzyme phosphoglycerate kinase catalyses the reduction of the carboxyl group of 1,3BPG to form an aldehyde instead. This reaction also releases an inorganic phosphate molecule which is subsequently used as energy for the donation of electrons from the conversion of NADPH to NADP+. Overseeing this latter stage of the reaction is the enzyme glyceraldehyde-phosphate dehydrogenase. In oxygen transfer During normal metabolism in humans approximately 20% of the 1,3BPG produced does not go any further in the glycolytic pathway. It is instead shunted through an alternate pathway involving the reduction of ATP in the red blood cells. During this alternate pathway it is made into a similar molecule called 2,3-bisphosphoglyceric acid (2,3BPG). 2,3BPG is used as a mechanism to oversee the efficient release of oxygen from hemoglobin. Levels of this 1,3BPG will raise in a patients blood when oxygen levels are low as this is one of the mechanisms of acclimatization. Low oxygen levels trigger a rise in 1,3BPG levels which in turn raises the level of 2,3BPG which alters the efficiency of oxygen dissociation from hemoglobin. References External links 1,3BPG in Glycolysis and Fermentation Medical Dictionary reference for 1,3BPG 1,3BPG enzyme mechanisms 1,3BPG in Photosynthesis Photosynthesis Biomolecules Cellular respiration Organophosphates Glycolysis