Carbohydrate Metabolism I

This chapter focuses on glycolysis and the tricarboxylic acid cycle (TCA). Glucose transports to the cells are mediated by a family of transmembrane facilitative glucose transporters (GLUTs). In the gastrointestinal (GI) tract and renal tubule cells glucose is actively transported against the concentration gradient along with Na + mediated by sodium-dependent transporter (SGLT). The major glucose transporter (GLUT4) of muscle and adipose tissue cells is regulated by insulin. The chapter discusses the ten steps involved in glycolytic pathways. Three allosteric enzymes hexokinase, phosphofructokinase and pyruvate kinase mediated by positive and negative effectors regulate glycolysis. Insulin promotes glycolysis and glucagon has opposite effects. AMP activated protein kinase (AMPK) promotes glycolysis. It is noted that under anaerobic and limited oxygen supply the end product of glycolysis is lactate. In aerobic cell the end product is pyruvate, which is oxidized in the mitochondria. TCA cycle consists of series biochemical reactions in which two carbon atoms of acetyl-CoA is oxidized to CO 2 and the energy stored in the two carbon atoms is transferred to NAD + and FAD, yielding NADH and FADH 2 .