Question

Write any three significance of pentose phosphate pathway.

Answer 1

Hint: The pathway connects in three places with glycolysis. In non- plant cells, the PPP pathway occurs within the cytoplasm (along with glycolysis), so considerable “intermingling" of intermediates can and does occur. Erythrose-4-phosphate is a very important precursor of aromatic amino acids and ribose-5-phosphate is an important precursor for creating nucleotides.

Complete answer: The pentose phosphate pathway (also called the phosphogluconate pathway and therefore the hexose monophosphate shunt) could be a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses (5-carbon sugars) also as ribose 5-phosphate, a precursor for the synthesis of nucleotides. While the pentose phosphate pathway does involve oxidation of glucose, its primary role is anabolic instead of catabolic. The pathway is particularly important in red blood cells (erythrocytes).
There are two distinct phases within the pathway. The primary is the oxidative phase, during which NADPH is generated, and therefore the second is the non-oxidative synthesis of 5-carbon sugars. For many organisms, the pentose phosphate pathway takes place within the cytosol; in plants, most steps occur in plastids.

Significance of Pentose-Phosphate-Pathway:
I. It provides an alternative route for carbohydrate breakdown and provides Ribose sugars for the synthesis of nucleic acids.
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 the pentose phosphate pathway.
III. It plays an important role in fixation of \[C{O_2}\] in photosynthesis through Ribulose-5-Phosphate. (Ribulose 1, 5-bisphosphate derived from Ribulose-5-Phosphate is the primary acceptor of CO$_2$ in photosynthesis).

Note: it's important to acknowledge that the PPP pathway isn't a “top-down" pathway, with all the intermediates derived from a starting G6P. All of the reactions are reversible, so that, for instance, fructose-6-phosphate and glyceraldehyde-3-phosphate from glycolysis can reverse the last reaction of the previous paragraph to supply a method of synthesizing ribose-5-phosphate non-oxidatively. The pathway also provides a mechanism to cells for metabolizing sugars, like ribulose-5-phosphate. Within the bottom line of the pathway, the direction the pathway goes and also the intermediates it produces are determined by the wants of, and intermediates available to, the cell.