Glucose is broken down into CO2 and water during aerobic respiration. This is the principals pathway of respiration. But sometimes, oxidation of glucose takes place by another pathway, which is called Pentose Phosphate Pathway (PPP). In pentose pathway, glucose phosphate (c) produced during, the early stages of glycosis, are oxidized to give rise to b-phosphor gluconate. This reaction takes place in the presence of the enzyme, glueose-6-phosphate dehydrogenase and generates NADPH.
The 6-phosphogluconate molecule is further oxidized by the enzyme, 6-phosphogluconate dehydrogenase. As a result of this, one molecule each of ribulose —5 —phosphate, carbon dioxide and NADPH are produced. Ribulose — 5- phosphate undergoes many changes produce glycolytic intermediate, such as glyceraldehyde-3-phosphate and fructose-6-phosphate. The various reactions of the cycle take place in the cell cytoplasm.