Glycolysis Handwritten Notes

Carbohydrates Glycolysis: Glycolysis also called Embden-Meyerhof Parnas Pathway or (EMP), is the process of catabolism of glucose, which occurs either in the presence of oxygen (aerobic) in tissue such as liver, or during lack of oxygen (anaerobic glycolysis) in muscle. Enzymes of the glycolytic pathway are present in the extramitochomdrial compartment of the cell. (Steps) Various reactions of the glycolytic pathway are as; Step No 1: Phosphorylation (activation) of Glucose. Firstly, glucose is phosphorylated and converted to glucose-6-phosphate by the enzyme Hexokinase. It is irreversible reaction, which requires ATP & Mg2+. This is referred to as activation of Glucose. Glucose --(Hexokinase/Glucokinase, Mg2+, ATP --> ADP)--> Glucose-6-phosphate. Hexokinase is allosterically inhibited by glucose-6-phosphate and has high affinity (low km) for Glucose. It is present in all extrahepatic tissues. Step 2: Isomerization of Glucose-6-phosphate: Glucose-6-phosphate is converted in a freely reversible reaction to Fructose-6-phosphate by the enzyme Phosphohexose Isomerase. Glucose-6-phosphate --(Phosphohexose Isomerase)--> Fructose-6-phosphate. Step 3: Phosphorylation of Fructose-6-phosphate: Fructose-6-phosphate is phosphorylated by an allosteric enzyme phosphofructokinase and is converted to fructose-1,6-bisphosphate. Fructose-6-Phosphate --(ATP, Mg2+, Phosphofructokinase, ADP)--> Fructose-1,6-bisphosphate Step 4: Cleavage of fructose-1,6-bisphosphate: Fructose-1,6-bisphosphate (a hexose) is cleaved to two trioses, called 3-phosphoglyceraldehyde (G3P) and dihydroxyacetone phosphate. This reaction is catalysed by the enzyme Aldolase. Fructose-1,6-bisphosphate --(Aldolase)--> 3-phosphoglyceraldehyde + Dihydroxyacetone phosphate Step 5: Isomerisation of Dihydroxyacetone Phosphate: Subsequently, since only 3-phosphoglyceraldehyde enters the pathway, dihydroxyacetone phosphate is converted to 3-phosphoglyceraldehyde by the enzyme Phosphotriose Isomerase. Dihydroxyacetone Phosphate --(Phosphotriose Isomerase)--> 3-phosphoglyceraldehyde. Step 6: Oxidative phosphorylation of G3P: G3P dehydrogenase converts 3-phosphoglyceraldehyde to 1,3-bisphosphoglycerate. This reaction requires NAD+ and Inorganic Phosphate (Pi). Glyceraldehyde-3-Phosphate --(G3P dehydrogenase, 2Pi, 2NAD+ --> 2NADH + 2H+)--> 1,3-bisphosphoglycerate. Step 7: Transfer of Phosphate from 1,3-diphosphoglycerate to ADP: 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate. This reaction is catalysed by the enzyme Phosphoglycerate Kinase. 1,3-bisphosphoglycerate --(Phosphoglycerate Kinase, Mg2+, ADP --> ATP)--> 3-phosphoglycerate. Step 8: Isomerization of 3-phosphoglycerate: Thereafter, 3-phosphoglycerate is converted to 2-phosphoglycerate. This reaction is catalysed by the enzyme Phosphoglycerate Mutase. In this reaction, 2,3-bis-phosphoglycerate (2,3-BPG) acts as Coenzyme. 3-phosphoglycerate --(2,3-BPG, Phosphoglycerate Mutase)--> 2-phosphoglycerate. Step 9: Dehydration of 2-phosphoglycerate: In this step, Enolase converts 2-phosphoglycerate to high energy compound called Phosphoenolpyruvate. 2-phosphoglycerate --(Enolase, Mg2+/Mn2+ --> H2O)--> Phosphoenolpyruvate. Enolase requires Mg2+/Mn2+ for its activity. This enzyme is inhibited by fluoride. Step 10: Transfer of Phosphate from phosphoenolpyruvate: Phosphoenolpyruvate is converted to pyruvate irreversibly. This reaction is catalysed by an enzyme Pyruvate Kinase. A molecule of ATP is also synthesized. Phosphoenolpyruvate --(Pyruvate Kinase, Mg2+, ADP --> ATP)--> Pyruvate