The ring-closing reaction makes carbon C-1 chiral , too, since its four bonds lead to -H, to -OH, to carbon C-2, and to the ring oxygen. These four parts of the molecule may be arranged around C-1 (the anomeric carbon ) in two distinct ways, designated by the prefixes "α-" and "β-". When a glucopyranose molecule is drawn in the Haworth projection , the designation "α-" means that the hydroxyl group attached to C-1 and the -CH 2 OH group at C-5 lies on opposite sides of the ring's plane (a trans arrangement), while "β-" means that they are on the same side of the plane (a cis arrangement). Therefore, the open-chain isomer D -glucose gives rise to four distinct cyclic isomers: α- D -glucopyranose, β- D -glucopyranose, α- D -glucofuranose, and β- D -glucofuranose. These five structures exist in equilibrium and interconvert, and the interconversion is much more rapid with acid catalysis .
But in living organisms, the oxidation of glucose contributes to a series of complex biochemical reactions which provides the energy needed by cells. The first step in the breakdown of glucose in all cells is glycolysis , producing pyruvate which is the starting point for all other processes in cellular respiration . In cells where oxygen is present ( aerobic respiration ) these processes have been modeled in the TCA or Krebs cycle . A major part of the use of the energy from glucose oxidation is the conversion of ADP to ATP , with the energy-rich molecule ATP being subsequently used as the energy currency of the cell.