2024-25 Anaerobic Metabolism (WITH ANSWERS) PDF

Faculty of Life Sciences & Medicine Dr. Lauren Albee MBBS- NAM Department of Biochemistry Lecture: Glucose metabolism: glycolysis Anaerobic metabolism  MBBS-NAM Glucose metab...

Faculty of Life Sciences & Medicine Dr. Lauren Albee MBBS- NAM Department of Biochemistry Lecture: Glucose metabolism: glycolysis Anaerobic metabolism  MBBS-NAM Glucose metabolism: glycolysis Dr. Lauren Albee Biochemistry and Molecular Biology Chapters 11 (p 181- 187) & 13 (p210-215) Available as an e-textbook at https://bibliu.com/app/#/signinPage 2  Learning outcomes After this lecture you should be able to: a) draw the structures of glucose and glycogen b) outline the metabolic events for the conversion of glucose to pyruvate in the glycolysis pathway c) explain the formation of ATP from ADP by ‘substrate level phosphorylation’. d) describe the processes for the regeneration of NAD+ from NADH under aerobic and anaerobic conditions, and the role of lactate dehydrogenase in muscle etc. e) give an example of a control mechanism in the regulation of glycolysis f) summarise the roles of glycolysis in different tissues, e.g. red blood cells 3  Structure and function of glucose and glycogen Glucose Glycogen Monosaccharide Polysaccharide Approx. 10 g in plasma Osmotically active Approx. 400 g in tissue stores Immediate energy source – glycolysis Low osmolarity (this lecture) Medium term fuel source Synthesis from non-carbohydrate Synthesis and breakdown (later sources – gluconeogenesis (later lecture) lecture) 4  Glycolysis: key points Definition: glucose C6 2 pyruvate C3 Location: cytosol (10 soluble enzymes) Tissues: all tissues Functions: ‘energy’ trapping (ATP synthesis) intermediates for fat synthesis intermediates for amino acid synthesis 5 Sources of Glucose for Glycolysis Sugars & starch from diet Breakdown of stored glycogen from the liver Recycled glucose (from lactic acid or amino acids or glycerol) 6 Summary Diagram of the Glycolysis Pathway Glyceraldehyde- 3-phosphate Pi Glyceraldehyde- NAD+ 3-phosphate dehydrogenase NADH + H+ D-Glucose Hexokinase ATP Fructose 6-phosphate or Glucokinase 1,3-Bisphosphoglycerate ADP ATP Phosphofructo- ADP kinase 3-Phosphoglycerate ADP kinase ATP 2-Phosphoglycerate Enolase H2O Glucose 6-phosphate Phosphohexose 3-Phosphoglycerate isomerase Fructose 1,6-bisphosphate Phosphoenolpyruvate Phospho- Aldolase glycerate Pyruvate ADP mutase kinase ATP Triose phosphate isomerase Glyceraldehyde- 2-Phosphoglycerate Fructose 6-phosphate Pyruvate 3-phosphate Dihydroxyacetone 7 phosphate The 10 Reactions of Glycolysis can be grouped into 4 Stages: Activation (using up ATP ) Splitting the 6 C sugar into half Oxidation (removing 2H atoms) Synthesis of ATP 8  Activation stages of glycolysis Glucose ATP Hexokinase Reactio ADP n1 Glucose 6-phosphate Phosphohexose isomerase Reaction 2 Fructose 6-phosphate ATP Phosphofructokinase Reaction 3 ADP Fructose 1,6-bisphosphate 9 Reaction Hexokinase 1 or Glucokinase ATP ADP D-Glucose Glucose 6-phosphate Trapping glucose within the cell by adding a negatively charged phosphate (will that diffuse through the membrane?) Hexokinase is in all tissues (except for the liver) Glucokinase is in the liver 10  Hexokinase vs Glucokinase Hexokinase Glucokinase All cells except liver Liver only Lower Km Higher Km Lower Vmax Higher Vmax Inhibited by Glucose-6- Not inhibited by phosphate Glucose-6-phosphate 11  The liver is able to generate glucose to Why maintainare there blood glucose concentrations (refer tothese lecture 18). differences Thus the liver does notin want to the isoforms compete with the brain for glucose when blood glucose levels are low. of the Therefore the liver will have a higher muscle? Km and also a higher Vmax (useful if the liver needs to store excess glucose) 12 Reaction 2 Phosphohexose isomerase Glucose 6-phosphate Fructose 6-phosphate Boring reaction – switch from an aldose to a ketose sugar 13 Reaction 3 Phosphofructo- kinase ATP ADP Fructose 6-phosphate Fructose 1,6-bisphosphate 14 Reaction 3 – Very important reaction Phosphofructo- kinase ATP ADP Fructose 6-phosphate Fructose 1,6-bisphosphate Very important reaction! Key regulatory step in glycolysis (see later slides) 15  Splitting of 6C Sugar to 3C Units Fructose 1,6-bisphosphate Aldolase Glyceraldehyde Dihydroxyacetone 3-phosphate phosphate 16 Reactions 4 &5 Fructose 1,6-bisphosphate Reaction 4 Aldolase Triose Reaction 5 Phosphat Glyceraldehyde e Dihydroxyacetone 3-phosphate isomeras phosphate 17 e  Oxidation step Glyceraldehyde Reaction 3-phosphate 6 – Very importa nt NAD + P + i Glyceraldehyde- reaction 3-phosphate All!reactions will now dehydrogenase NADH + H + occur twice because you have two 3 carbon molecules from 1 1,3-Bisphosphoglycerate molecule of glucose 18 Reaction 6 The NADH produced will be used in oxidative Glyceraldehyde phosphorylation to generate 3-phosphate ATP. Pi Glyceraldehyde- NAD+ 3-phosphate Not super useful at this dehydrogenase NADH + H+ stage, but it will be needed if oxygen is low (more in a few slides) 1,3-Bisphosphoglycerate 19  ATP synthesis stages 1,3-Bisphosphoglycerate ADP 3-Phosphoglycerate Reaction 7 ATP kinase 3-Phosphoglycerate Phosphoglycerate Reaction 8 mutase 2-Phosphoglycerate Reaction 9 H2O Enolase Phosphoenolpyruvate Reaction ADP Pyruvate ATP kinase 10 Pyruvate 20  Reaction 7 – Very important reaction ‘Substrate level phosphorylation’ 1,3-Bisphosphoglycerate ADP ATP is produced by substrate level Phosphoglycerate kinase phosphorylation! ATP 2 molecules of ATP are produced at this step – why? Because you do each reaction twice! 3-Phosphoglycerate 21  Reaction 8 - Isomerisation Phosphoglycer ate mutase 3-Phosphoglycerate 2-Phosphoglycerate Boring reaction, just move the phosphate around 22 Reaction 9 Another boring reaction but you want to know the product 2-Phosphoglycerate of this reaction – PEP. Enolase PEP will come up again when we discuss anaplerotic filling of the TCA cycle and in gluconeogenesis Phosphoenol pyruvate 23  Reaction 10 – Very important reaction ‘Substrate level phosphorylation’ Phosphoenolpyruvate ATP is produced! ADP Pyruvate Again, ATP is produced by kinase substrate level phosphorylation. ATP Note this enzyme is IRREVERSIBLE Pyruvate 24  Summary slide: Yields of ATP from Glycolysis Early stages use 2 ATP Later stages make 4 ATP Net yield = 2 ATP (Plus further ATP from mitochondrial metabolism from 2 NADH that were produced) 25  Anaerobic Glycolysis When oxygen supplies to the tissues are limited, pyruvate is not metabolised to CO2 Pyruvate converted to lactate in order to convert the cofactor NADH back to NAD + pyruvate + NADH + H+ → NAD+ + lactate 26  Reaction Catalysed by Lactate Dehydrogenase It is a reversible reaction that uses Pyruvate NADH + H+ NADH when converting in in pyruvate to lactate liver muscle NAD + L-Lactate 27  Metabolic fates of Pyruvate no O2 Pyruvate or no micro organisms mitochondria only Lactate Acetyl CoA Ethanol O2 excess calories intake present Citric acid Fatty acids cycle O2 present CO2 28  Regulation of glycolysis The pathway is under Allosteric control Hormonal control We will look at one example of allosteric control. Hormonal control exists but I do not require you to understand that currently. 29  Feedback inhibition of glycolysis by allosteric regulation Allosteric control of the Fructose 6-phosphate ATP enzyme ATP Citrate Phosphofructo- phosphofructokinase. kinase AMP ADP Think about the cell’s needs at any moment in time. Does it have plenty of energy? If so , does it need to be doing glycolysis or storing Fructose 1,6-bisphosphate 30 Allosteric inhibition of phosphofructokinase by ATP 31  Specialised functions in Tissues Skeletal muscle: ATP production during intense exercise need energy quickly Red blood cells:only pathway for ATP production (no mitochondria) Brain: major source of ATP (cannot use fats as 32  Summary of Glycolysis Main catabolic pathway using glucose, present in all tissues Only energy yielding pathway that can function either in aerobic or anaerobic conditions (red cells & skeletal muscle) Energy yields are low (2 ATP) but the pyruvate can enter the mitochondria for further ATP production Pathway produces intermediates for fats, 33 etc  Discoveries and dilemmas ‘Extras’ to think about and puzzle over No need to learn this extra information – though some may come back in later lectures. 34  The Warburg effect Tumour cells preferentially generate energy through anaerobic glycolysis Tumours produce lactate at up to 200x the rate of ‘healthy’ cells, even when mitochondria are intact Maria V. Liberti, Jason W. Locasale The Warburg Effect: How Does it Benefit Cancer Cells? Trends in Biochemical Sciences , Volume 41, Issue 3, 2016, 211–218 http://dx.doi.org/10.1016/j.tibs.2015.12.001 Known for > 90 years, intensively studied recently. Function still unknown, but may be useful as a diagnostic tool and/or therapeutic target. 35  MCQ 1 1. What are the end products of glycolysis under aerobic and anaerobic conditions? A. carbon dioxide and lactate B. acetyl CoA and lactate C. pyruvate and lactate D. pyruvate and acetyl CoA E. acetyl CoA and pyruvate 36  MCQ 2 2. In which three cell types is the glycolysis pathway of particular importance? A. Brain, skeletal muscle, and red blood cells B. Adipose tissue, skeletal muscle, and red blood cells C. Brain, liver, and red blood cells D. Liver, skeletal muscle, and red blood cells E. Brain, liver, and skeletal muscle 37  MCQ 3 3. The net yield of ATP from anaerobic glycolysis is: A. 1 ATP per glucose molecule B. 2 ATP per glucose molecule C. 4 ATP per glucose molecule D. 6 ATP per glucose molecule E. 8 ATP per glucose molecule 38 Summary Diagram of the Glycolysis - extra information for MCQ 3 Glyceraldehyde- 3-phosphate Pi Glyceraldehyde- NAD+ 3-phosphate dehydrogenase NADH + H+ D-Glucose Hexokinase ATP Fructose 6-phosphate or Glucokinase 1,3-Bisphosphoglycerate ADP ATP Phosphofructo- ADP kinase 3-Phosphoglycerate ADP kinase ATP 2-Phosphoglycerate Enolase H2O Glucose 6-phosphate Phosphohexose 3-Phosphoglycerate isomerase Fructose 1,6-bisphosphate Phosphoenolpyruvate Phospho- Aldolase glycerate Pyruvate ADP mutase kinase ATP Triose phosphate isomerase Glyceraldehyde- 2-Phosphoglycerate Fructose 6-phosphate Pyruvate 3-phosphate Dihydroxyacetone 39 phosphate  MCQ 4 4. Which two reactions in glycolysis result in direct production of ATP by substrate level phosphorylation? Those catalysed by: A. hexokinase and pyruvate kinase B. aldolase and pyruvate kinase C. 3-phosphoglycerate kinase and pyruvate kinase D. hexokinase and 3-phosphoglycerate kinase E. aldolase and 3-phosphoglycerate kinase 40