Significance of Pentose-Phosphate-Pathway

(i) It provides alternative route for carbohydrate breakdown.

(ii) It generates NADPH molecules which are used as reductants in biosynthetic processes under conditions when NADPH molecules are not generated by photosynthesis. It is therefore, especially important in non-photosynthetic tissues such as in differentiating tissues, ger­minating seeds and during periods of darkness. Production of NADPH is not linked to ATP generation in pentose phosphate pathway.

(iii) It provides Ribose sugars for the synthesis of nucleic acids.

(iv) It plays important role in fixation of CO2 in photosynthesis through Ribulose-5-Phosphate. (Ribulose 1, 5-bisphosphate derived from Ribulose-5-Phosphate is the primary acceptor of CO2 in photosynthesis).

(v) It provides Erythrose-4-phosphate which is required for the synthesis of shikimic acid. The latter is precursor of aromatic ring compounds.

(In addition to the above pathway for the oxidation of carbohydrates, still other routes have been identified in some micro-organisms and enzyme systems discovered. In all such cases the initial steps of glucose oxidation differ from glycolysis but ultimately pyruvic acid is produced.

On such alternative pathway is Entner Doudoroff Pathway which is shown in Fig. 16-19. In this pathway the carboxylic group of pyruvic acid is derived from carbon No. 1 of glucose molecule (in glycolysis it was derived from C-No. 3 or 4.).