Glycolysis (Embden-Meyerhof pathway -Carbohydrate metabolism)

Glycolysis is derived from the Creek words (glycose-sweet or sugar; lysis-dissolution).

1. Glycolysis Mr. S Maheen Abdul Rahman, M. Pharm. Assistant Professor Department of Pharmaceutical Chemistry PA College of Pharmacy (PACP) Mangalore, Karnataka.

2. Carbohydrates are the major source of energy for the living cells. As such, carbohydrates are the first cellular constituents, synthesized by green plants during photosynthesis from carbon dioxide and water, on absorption of light. Thus, light is the ultimate source of energy for all biological processes. Carbohydrate Metabolism

3. Major pathways of carbohydrate metabolism Glycolysis (Embden-Meyerhof pathway): The oxidation of glucose to pyruvate and lactate. Citric acid cycle (Krebs or tricarboxylic acid cycle TCA) : The oxidation of acetyl CoA to CO2. Krebs cycle is the final common oxidative pathway for carbohydrates, fats or amino acids, through acetyl CoA Gluconeogenesis: The synthesis of glucose from non-carbohydrate precursors (amino acids, glycerol etc.). Glycogenesis : The formation of glycogen from glucose. Glycogenolysis : The breakdown of glycogen to glucose Hexose monophosphate shunt-HMP : This pathway is an alternative to glycolysis and TCA cycle for the oxidation of glucose (directly to carbon dioxide and water)

4. Entry of glucose into cells Glucose concentration is very low in the cells compared to plasma (for humans < 100 mg/dl). However, glucose does not enter the cells by simple diffusion. Two specific transport systems are recognized for the entry of glucose into the cells. Insulin-independent transport system of glucose Insulin-dependent transport system Glucose transporters: GLUT1-5 and GLUT-7

5. Glycolysis Glycolysis is derived from the Creek words ( glycose-sweet or sugar; lysis-dissolution ). It is a universal pathway in the living cells. The complete pathway of glycolysis was elucidated in 1940 . This pathway is often referred to as Embden-Meyerhof pathway (E.M, pathway) in honour of the two biochemists who made a major contribution to the knowledge of glycolysis. Glycolysis is defined as the sequence of reactions converting glucose (or glycogen) to pyruvate or lactate, with the production of ATP molecules

6. Reactions of glycolysis The pathway can be divided into three distinct phases Energy investment phase or priming stage Splitting phase Energy generation phase

7. 2-Mark

8. Pasteur effect: The Pasteur effect refers to how the presence of oxygen in cells decreases the rate of glycolysis and suppresses lactate accumulation. It occurs in animal tissues and microorganisms, and indicates that cells shift from glycolysis to more efficient oxidative phosphorylation for ATP production when oxygen is available. Crabtree effect: The Crabtree effect, named after the English biochemist Herbert Grace Crabtree.

9. Increasing concentrations of glucose accelerates glycolysis (the breakdown of glucose) which results in the production of appreciable amounts of ATP through substrate-level phosphorylation. This reduces the need of oxidative phosphorylation done by the TCA cycle via the electron transport chain and therefore decreases oxygen consumption. The phenomenon is believed to have evolved as a competition mechanism

10. REFERENCE BOOK: Text book of biochemistry by Satyanarayana and chakrapani