Redox Energetics in Metabolism PDF

REDOX Energetics in Metabolism Lecture Objectives 1. Understand the nature of REDOX reactions and their role in energy generation to answer the following questions: What is an electron donor? What is an electron acceptor? Which molecule is oxidized? Which is reduced? What role does re...

REDOX Energetics in Metabolism Lecture Objectives 1. Understand the nature of REDOX reactions and their role in energy generation to answer the following questions: What is an electron donor? What is an electron acceptor? Which molecule is oxidized? Which is reduced? What role does reduction potential play in spontaneous REDOX reactions and energy generation? 2. Be able to use a table of reduction potentials for various compounds to predict the direction of a reaction and the amount of energy generated. Metabolism Reduced Reduced biological Sunlight geological compounds compounds (minerals) (sugars) Lithotrophy Phototrophy Organotrophy CATABOLISM Long-term Energ y energy Short-term energy storage ANABOLISM Biosynthesis storage Carbon, ATP nitrogen, water Energy Generation Predominant energy source is electricity □ Movement of electrons releases energy □ Electrons move from molecule A (donor) to molecule B (acceptor) Redox reactions: □Reduced electron donor becomes oxidized □Oxidized electron acceptor becomes reduced Energy Generation Electron Transfer: REDOX reactions A molecule undergoes oxidation when it loses one or more electrons and a molecule undergoes reduction when it gains one or more electrons. These two reactions must be coupled within a single REDOX reaction : H2 + ½ O2 ➔ H20 Electron Transfer: REDOX reactions A molecule’s reduction potential E0’ describes its tendency to become reduced (accept electrons) and is measured in volts (V). Poor electron acceptor Good electron but good electron acceptor but poor donor electron donor 1-E0’ = 1.237 V E0’ = - 0.421 V E0’ = + 0.816 V The greater the difference in E0’ between two compounds, ΔE, the greater the free energy available when electron transfer happens. Good Electron Donor Good Electron Acceptor Nutrition and Metabolism Nutrient adaptations help explain microbial niches and cell differentiation. Vibrio fischeri Geobacter metallireducens Agrobacterium tumifaciens Metabolism Cellular growth and reproduction requires:  uptake of organic nutrients into the cytoplasm  conversion of these nutrients into energy: Catabolism  conversion of these nutrients into cellular building blocks: Anabolism Building the Cell  Energy generation  Catabolism  Also called organotrophy  Using organic molecules to make cellular energy  Other forms of energy generation: phototrophy (light) and lithotrophy (minerals)  Energy consumption  Anabolism  Using energy and nutrients to build new cell components  Metabolism  Balance between catabolism and anabolism Bacterial Metabolism Overview Reduced Reduced Sunlight geological biological compounds compounds Lithotrophy Phototrophy Organotrophy Long-term Energ energy y energy storage Short-term Biosynthesis storage carbon ATP nitrogen PMF NAD(P) Metabolism  All life requires: Energy that comes from electron flow  REDOX reactions are required for energy generation  Forex., redox reactions drive glycolysis and respiration to create the PMF, and the PMF is used to make ATP Energy and nutrients to make new cell parts Energy Generation  Predominant energy source is electricity  Movement of electrons through spontaneous redox reactions releases energy  Spontaneous reactions with –i1G  free energy released used to make cellular energy  Requires electron donor and electron acceptor  Energy commonly stored in:  Phosphorylated chemicals - ATP  Concentration gradients - PMF  Reduced chemicals - NADH Energy Generation Requires  An initial electron donor  Organotrophs  Organic molecules are electron donors  NADH, sugars, amino acids, lipids, etc. A final electron acceptor  Organic molecules  Sugars  Fermentation  Inorganic molecules  O2, nitrogen, iron, etc.  Respiration Energy Generation  Predominant energy source is electricity  Movement of electrons releases energy  Electrons move from molecule A (donor) to molecule B (acceptor)  Redox reactions: Reduced electron donor becomes oxidized Oxidized electron acceptor becomes reduced Electron Transfer: REDOX reaction Electron Transfer: REDOX reaction A molecule becomes oxidized when it loses one or more electrons and a molecule becomes reduced when it gains one or more electrons. These two reactions must be coupled within a single REDOX reaction : H2 + ½ O2  H20 Electron Transfer: REDOX reactions A molecule’s reduction potential E ’ describes its tendency 0 to become reduced (accept electrons) and is measured in volts (V). Poor electron acceptor Good electron but good electron acceptor but poor donor electron donor 1-E0’ = 1.237 V E0’ = - 0.421 V E0’ = + 0.816 V The larger the difference in E0’ between two compounds, ΔE, the larger the free energy released when electron transfer happens. Good Electron Donor Good Electron Acceptor A molecule’s reduction potential E0’ describes its tendency to become reduced (accept Good Electron Donor Good Electron Acceptor The larger the difference in E0’ between two compounds, ΔE, the larger the free energy released when electron transfer happens. Good Electron Donor Good Electron Acceptor Bacterial Metabolism Overview Reduced Reduced Sunlight geological biological compounds compounds Lithotrophy Phototrophy Organotrophy Long-term Energ energy y energy storage Short-term Biosynthesis storage carbon ATP nitrogen PMF NAD(P) Metabolism  Microbes have great metabolic diversity  Electron donors  Organotrophy: exogenous (extracellular) organic molecules  Lithotrophy: exogenous (extracellular) inorganic molecules  Phototrophy: exogenous (extracellular) light energy to reduce intracellular compounds, then use these as electron donor  Electron acceptors  Fermentation: endogenous (intracellular) organic molecules  Respiration: exogenous (extracellular) inorganic molecules Metabolism  Energy generation  Organotrophy  Oxidization of organic molecules for energy  For ex., glucose  Energy can be stored in:  Phosphorylated chemicals - ATP  Concentration gradient - PMF  Reduced chemicals – NAD(P)H Organotrophy  Wide range of organic compounds digested  Variety of simple sugars  Converted to glucose or enter glycolysis pathway  Polysaccharides  Converted to glucose  Lipids  Converted to Acetyl- CoA  Amino acids  Glucose Oxidation Three common routes:  Glycolysis (Embden-Meyerhof-Parnas, EMP) pathway  Entner-Doudoroff pathway  Pentose phosphate pathway Summary of Glycolysis  Glucose is activated  Phosphorylated twice  Activatedphospho- sugar is split  Converted to glyceraldehyde 3- phosphate  Glyceraldehyde-3-P is then oxidized  Energy stored as ATP  End product is  Glycogen Activated by ADP (sign of LOW energy) Repressed by ATP Substrate-level (sign of HIGH phosphorylation energy)  critical REDOX Glycogen reaction Spontaneous REDOX Reaction REDOX reaction drives sugar phosphorylation electron donor ––ΔG electron acceptor Spontaneous REDOX Reaction REDOX reaction drives sugar phosphorylation electron donor –ΔG electron acceptor Glycolysis Yields ATP phosphate groups used to make ATP Good Electron Donor Good Electron Acceptor Metabolism  Microbes have great metabolic diversity  Electron donors  Organotrophy: exogenous (extracellular) organic molecules  Lithotrophy: exogenous (extracellular) inorganic molecules  Phototrophy: exogenous (extracellular) light energy to reduce intracellular compounds, then use these as electron donor  Electron acceptors  Fermentation: endogenous (intracellular) organic molecules  Respiration: exogenous (extracellular) inorganic molecules Fermentation  Glycolysis: glucose is oxidized to make ATP  NADH is produced in reactions  Must be oxidized back to NAD+ to continue glycolysis  Pyruvate builds up  Must be eliminated  Fermentation  Donate NADH electrons to endogenous acceptor  Donate electrons back to pyruvate  Or to Acetyl-CoA produced from pyruvate  Convert pyruvate (or Acetyl-CoA) into other products  Either useful for the cell or easy to eliminate Good Electron Donor Good Electron Acceptor Fermentation  ATP formed by substrate- level phosphorylation during glycolysis  Pyruvate is used as an endogenous electron acceptor for the oxidation of Fermentation in Anaerobic Muscle Fermentation  ATP formed by substrate- level phosphorylation during glycolysis  Acetyl-CoA is used as an endogenous electron acceptor for the oxidation of NADH Many different Fermentation pathways Massachusetts “Anaerobic Digestion & Organics Diversion” program funds innovation and research into large-scale anaerobic digesters.