Chapter 20: Pentose Phosphate Pathway & Hexose Metabolism

The pentose phosphate pathway is a vital cytosolic process that diverges from traditional energy production to generate NADPH and ribose-5-phosphate, which are indispensable for biosynthesizing lipids, maintaining cellular antioxidant defenses through glutathione, and forming the structural foundations of nucleic acids like DNA and RNA. Clinical significance is highlighted through genetic conditions such as glucose-6-phosphate dehydrogenase deficiency, a common mutation that protects against malaria but leaves red blood cells vulnerable to oxidative damage and hemolytic anemia. The text further explores the uronic acid pathway, which facilitates the detoxification of foreign compounds (xenobiotics) and synthesizes glucuronic acid for conjugation reactions. It explains the evolutionary lack of vitamin C synthesis in humans due to specific enzyme absences. Fructose metabolism is described as a rapid process that bypasses major regulatory checkpoints in the liver, explaining why high intake can lead to increased fat production, elevated cholesterol, and uric acid accumulation associated with gout. Additionally, the chapter details how galactose is converted for use in the body and the severe health impacts of galactosemia, where the inability to process this sugar leads to cataracts and liver dysfunction. Finally, the discussion covers the sorbitol pathway’s role in diabetic complications and the conversion of glucose into amino sugars necessary for creating essential glycoproteins and tissue structures.