Textbook - BIOLOGICAL CHEMISTRY - Gubsky Yu.I. - 2000

Chapter III. METABOLISM OF MAJOR CLASSES OF BIOMOLECULES

CHAPTER 11. CARBOHYDRATE METABOLISM. I. AEROBIC AND ANAEROBIC GLUCOSE OXIDATION

11.4. ENERGETICS OF GLYCOLYSIS AND AEROBIC GLUCOSE OXIDATION

Class="center">Energetics of Glycolysis

Taking into account two ATP molecules consumed in The First stage of glycolysis (the hexokinase and Phosphofructokinase reactions) and four ATP molecules generated In the second stage (the phosphoglycerate kinase and Pyruvate kinase reactions), the overall process of aerobic and anaerobic glycolysis can be represented by the following equation:

The formation of ATP molecules during glycolytic reactions via the direct transfer of high-energy phosphate groups from 1,3-BPG and PEP to ADP is known as substrate-level phosphorylation ("phosphorylation at the substrate level").

Energetics of AEROBIC GLUCOSE OXIDATION

To calculate the total number of ATP molecules generated under conditions of complete glucose oxidation to carbon dioxide and Water, the following factors are taken into account:

- the number of ATP molecules produced at the aerobic glycolysis stage (2 ATP molecules);

- the number of ATP molecules produced via the mitochondrial oxidation of two molecules of glycolytic NADH (2x3 = 6 ATP molecules);

- the number of ATP molecules produced at the stage of Oxidative Decarboxylation of two pyruvate molecules via the mitochondrial oxidation of NADH generated in the pyruvate dehydrogenase reaction (2x3 = 6 ATP molecules);

- the number of ATP molecules produced through The oxidation of two acetyl-CoA molecules in The Tricarboxylic Acid Cycle (2x12 = 24 ATP molecules).

The overall equation for aerobic glucose oxidation, which accounts for ATP generated by substrate-level phosphorylation during the glycolytic phase and by Oxidative Phosphorylation in Cell/35.html">Mitochondria, is as follows:

Due to the significantly higher energetic efficiency of aerobic glucose oxidation compared to glycolysis, the latter process is considered an evolutionarily more primitive pathway of Glucose Catabolism that was of primary importance under conditions when oxygen was absent from the primordial Earth's atmosphere.