The Pentose Phosphate Pathway: Introduction

00:00 Metabolic Pathways has been compared to roadways as depicted on road maps. And if thats the case on the Pentose Phosphate Pathway is gonna be one of the more interconnective roadways that we find inside of cells. The Pentose Phosphate Pathway is a very important component of carbohydrate metabolism having multiple inputs and outputs as we shall see. Two of the steps of the Pentose Phosphate Pathway are oxidated in nature. And they synthesize about 60% of the cells NADPH. NADPH of course is necessary for making bigger and important molecules. The Pentose Phosphate Pathway generates intermediates for other pathways as well. The very important one is Ribose- 5 phosphate which is needed for making nucleotides. Erythrose-4 phosphate is necessary for making aromatic amino acids and aromatic amino acid metabolism. NADPH is I know that it is something this important for synthesizing of fatty acids and other molecules of the cell may need. NADPH is also needed to keep the important antioxidant glutathione reduced and protect the cell from reactive oxygen species. So, it contains numerous intermediates of glycolysis and gluconeogenesis and this provides for a lot of the pathways flexibility as we shall see. Now, one of the enzymes of the Pentose Phosphate pathways is also used in the Calvin Cycle and it’s known as transketolase. And important thing to realize about the Pentose Phosphate pathway is that unlike the way it’s commonly thought, the pathway doesn’t really have a start or an end. You will see end points but those end points are connected to other pathways and there are multiple points of the entry into the pathway and we’ll see some examples of that. The Pentose Phosphate pathway occurs exclusively in the cytoplasm of cells. The ten intermediates of the Pentose Phosphate Pathway are depicted in this figure. And I put them in the several groups based upon their sort of commonality. The first group are three intermediates from the pathway of glycolysis.

01:57 Glucose-6 phosphate, Fructose-6 phosphate and Glyceraldehyde-3 phosphate. The next two intermediates are important in other pathways Ribose- 5 phosphate, this I know for nucleotide metabolism and Erythrose-4 phosphate for making aromatic amino acids. The next three are irrelatively unusual relatively rare sugars that aren’t found too much outside the Pentose Phosphate pathway and include Ribulose-5 phosphate, Xylulose-5 phosphate and Sedoheptulose-7 phosphate. And the last two are sugar derude is that pretty much found only in the Pentose Phosphate pathway.