UCL BENG0004 2021 Glycolysis Lecture Notes PDF

BENG0004 Biochemistry and Molecular Biology Emily Kostas Lecture 16 Glycolysis  Glycolysis In E. coli and mammalian cells the set of enzymes and steps used to degrade glucose is called the glycolytic pathway. But...

BENG0004 Biochemistry and Molecular Biology Emily Kostas Lecture 16 Glycolysis  Glycolysis In E. coli and mammalian cells the set of enzymes and steps used to degrade glucose is called the glycolytic pathway. But this just means breaking glucose and there are several types of pathways known in nature that have a set of enzymes that break down glucose. They do not all use the same enzymatic steps. E. coli and mammalian cells use the Emden Meyerhof Parnas (EMP) pathway. Many bacteria use the Entner Doudoroff pathway (E. coli used the ED pathway for gluconate metabolism) and some other bacteria use the Phosphoketolase pathway. How does glucose get into cells? Prokaryotes: - In E. coli glucose is phosphorylated as it is being carried over the membrane by the PTS (the phosphotransferase system). - This enzyme system uses phosphoenol pyruvate, PEP, from lower down the glycolytic pathway as the phosphoryl donor. - PEP carries a high energy phosphate ester bond. - The direct phosphorylation of glucose prevents the glucose from leaving the cell and maintains a gradient of higher glucose outside. E. coli Glucose Glucose-6-phosphate How does glucose get into cells? Eukaryotes: - In eukaryotic cells glucose is transported across the cell membrane as glucose and inside the cell the enzyme Hexokinase uses ATP to phosphorylate the glucose to form glucose-6-phospate. Mammalian cell The EMP Glycolytic pathway ATP is used at two early stages and ATP is made at two in a mammalian cell later stages. 1 molecule of glucose (C6) is cleaved into two C3 molecules by the enzyme Fructose bisphosphate aldolase (enzyme 4) So from that point onwards there are two molecules of the C3 compounds. So the bottom half of the pathway generates 4 molecules of ATP. Net number of ATP from Glucose to lactate is 2. Net number of NADH is 2 up to pyruvate and normally these are reduced later in the electron transport chain and generate a lot of ATP if oxygen is present. The final step shown here where pyruvate is reduced to lactate and thus the NADH generated earlier is recycled back to NAD. This final step will not happen in most tissues, only in muscle during exercise and in some cancer cells. The EMP Glycolytic pathway in an E. coli cell PEP 1 ATP is used at one early stage and 1 PEP is used in the early pyruvate stage. ATP is made at two later stages. 1 molecule of glucose (C6) is cleaved into two C3 molecules by the enzyme Fructose bisphosphate aldolase (enzyme 4) So from that point onwards there are two molecules of the C3 compounds. So the bottom half of the pathway generates 3 molecules of ATP as one PEP is used to phosphorylate glucose. One ATP is used to make Fructose 1,6-bisphosphate. PTS Net number of ATP from Glucose to lactate is 2. PTS Net number of NADH is 2. These are reduced later in the electron transport chain and generate a lot of ATP if oxygen is present. Overview of Glycolysis energy generation Structures Glucose Glucose-6-phosphate Fructose-6-phosphate Fructose 1,6-bisphosphate Glyceraldehyde 3-phosphate 1,3-bisphosphoglycerate 3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate Pyruvate Energetics of glycolysis Energetics of glycolysis  Concentrations of glycolytic intermediates in a red blood cell Compound Concentration / mM Glucose 5.0 Glucose-6-phosphate 0.083 Fructose-6-phosphate 0.014 Fructose-1,6-bisphosphate 0.031 Dihydroxyacetone phosphate 0.14 Glyceraldehyde-3-phosphate 0.019 1,3-Bisphosphoglycerate 0.001 2,3-Bisphosphoglycerate 4.0 3-Phosphoglycerate 0.12 2-Phosphoglycerate 0.03 Phosphoenolpyruvate 0.023 Pyruvate 0.051 ATP 1.85 ADP 0.14 Pi 1.0 2,3-bisphosphoglycerate is found in red blood cells and not in other tissues. It has a role to play in binding to deoxy-haemoglobin and promoting release of the last molecules of oxygen. Biochemistry. 8th Edition. Berg, Tymoczko, Gatto Jr. and Stryer. W.H Freeman and Co Glycolysis Chapter 16 pages 449-465