Glycolysis Glycolysis ( Greek  glykys – sweet; lysis – splitting) involves the breakdown of glucose molecules through a series of reactions catalyzed by a set of enzymes such that a 6 – C sugar forms a 3 – C compound. Significance of Glucose in biological systems A major fuel source of the body hence occupies a central position in metabolism Most of the tissues require some amt. of glucose for their proper functions; however in brain the requirement is significant and erythrocytes which lack mitochondria rely on glucose as their metabolic fuel carrying out anaerobic glycolysis. In higher forms of life, glucose has three different fates.

Major pathway of glucose utilization in higher forms Glycogen (or starch, sucrose) GLUCOSE Ribose sugarPyruvate, lactate Ribose sugarPyruvate, lactate Fate of glucose in the body – may be stored in a complex form as glycogen; oxidized to pyruvate by glycolysis or oxidized to pyruvate by glycolysis or oxidized to pentose by Pentose phosphate pathway oxidized to pentose by Pentose phosphate pathway

Significance of Glycolysis It is the principal route for glucose metabolism and the metabolism of other hexoses (fructose, galactose) Its ability to function under anaerobic condition is of significance, as it allows skeletal muscle to function and survive under anoxic episodes by providing ATP However certain tissue like the heart muscle is adapted for aerobic performance, and hence possesses low glycolytic activity and survival rate under ischemic conditions In pathological conditions like fast growing cancer cells glycolysis proceeds at a higher rate than the requirement of TCA cycle, due which the large amts. of pyruvate formed gets converted to lactate producing a local acidic environment in the tumors.

Glycolysis under anaerobic condition Involves anaerobic degradation of glucose and is also termed as Fermentation in general During muscle contraction in anaerobic medium, lactate appears as the end product Anaerobic glycolysis however has a price, for it limits the amount of ATP generated per molecule of glucose, due which much more glucose is metabolized in anaerobic medium During anaerobic condition, mitochondrial re oxidation of NADH (formed during glycolysis) is impaired, which is then reoxidized to NAD by reducing pyruvate to lactate. When oxygen is supplied, the lactate then disappears. However, in aerobic condition, pyruvate forms the end product being further oxidised to CO 2 and water

Reactions of Glycolysis (An overview)

The First Stage of Glycolysis Called as Preparatory phase, which involves phosphorylation of glucose and its conversion to glyceraldehyde phosphate Called as Preparatory phase, which involves phosphorylation of glucose and its conversion to glyceraldehyde phosphate

The Second Stage of Glycolysis  Called as pay off phase which involves oxidative conversion of glyceraldehyde phosphate to pyruvate and coupled to the formation of ATP and NADH

Fate of Pyruvate Glucose glycolysis Anaerobic cond n 2 Pyruvate Anaerobic cond n 2CO 2 aerobic cond n 2 Ethanol + 2 CO 2 2 Lactate (in yeast) 2 Acetyl CoA (in contracting muscle, RBCs) citric acid cycle 4 CO H 2 O (animal, plant, and mo s under aerobic conditions)