Microbiology Chapter 13.1 – 13.2 PDF

CHAPTER 13.1 – 13.2 Energetics and Catabolism I Copyright © 2024 by W. W. Norton & Company, Inc. Chapter 13 Learning Objectives § Explain how microorganisms convert chemical potential energy into cellular energetics via Gibbs Free Energy. § Understand the difference between metabolic reactions that...

CHAPTER 13.1 – 13.2 Energetics and Catabolism I Copyright © 2024 by W. W. Norton & Company, Inc. Chapter 13 Learning Objectives § Explain how microorganisms convert chemical potential energy into cellular energetics via Gibbs Free Energy. § Understand the difference between metabolic reactions that yield energy (respiration, fermentation, and phototrophy) and those that require energy (biosynthesis and carbon fixation). § Discuss how a wide variety of catabolic substrates can be funneled into the central carbon metabolism. § Explain what energetic problems are solved by fermentation. 2 All living cells need energy to move and grow 3 Catabolism vs. Anabolism 4 Catabolism vs. Anabolism 5 Catabolism vs. Anabolism 6 13.1 Energy for Life § Every form of life, from a composting microbe to a human body, uses energy. § Energy is the ability to do work. Such as flagellar propulsion or cell growth 7 13.1 Energy for Life § Entropy is a measure of the disorder or randomness of a system. § Cells use energy to assemble simple, disordered molecules into complex, ordered forms such as cell components Anabolism (Decrease in Entropy) Catabolism (Increase in Entropy) 8 Enthalpy is the Measurement of Energy (Heat) in a System § ∆H is the heat transferred in and out of the system § Exothermic reactions release heat (i.e., heat is exiting the system) so total energy has decreased (negative ∆H) heat 9 Microbes Use Energy to Build Order § The local, temporary gain of energy enables the cell to grow. Continued growth requires a continual gain of energy and continual radiation of heat. 10 Microbes Use Energy to Build Order § What is true of the cell holds as well for the entire biosphere. Total metabolism of all life-forms ultimately dissipate most energy as heat. 11 Important Prefixes Carbon source for biomass Auto-: CO2 is fixed and assembled into organic molecules. Hetero-: Preformed organic molecules are acquired and assembled into new organic molecules. 12 Important Prefixes Carbon source for biomass Auto-: CO2 is fixed and assembled into organic molecules. Hetero-: Preformed organic molecules are acquired and assembled into new organic molecules. Energy source Photo-: Light absorption captures energy. Chemo-: Chemical reactions yield energy without absorbing light. 13 Important Prefixes Carbon source for biomass Auto-: CO2 is fixed and assembled into organic molecules. Hetero-: Preformed organic molecules are acquired and assembled into new organic molecules. Energy source Photo-: Light absorption captures energy. Chemo-: Chemical reactions yield energy without absorbing light. Electron source Litho-: Inorganic molecules donate electrons. Organo-: Organic molecules donate electrons. 14 Microbes use Diverse Energy Sources § Chemotrophy yields energy from electron transfer between chemicals. Chemoorganotrophy = electrons from organic compounds Chemolithotrophy = electrons from inorganic compounds 15 Microbes use Diverse Energy Sources § Chemotrophy yields energy from electron transfer between chemicals. Chemoorganotrophy = electrons from organic compounds Chemolithotrophy = electrons from inorganic compounds § Phototrophy yields energy from light absorption. Photoautotrophy = Absorption with CO2 fixation Photoheterotrophy = Absorption without CO2 fixation 16 Gibbs Free Energy Change § The direction of a reaction can be predicted by a thermodynamic quantity called Gibbs free energy change, ΔG. ΔG value of a reaction determines how much energy is potentially available to do work 17 Gibbs Free Energy Change § The value of ΔG is determined by changes in enthalpy and entropy. § ΔG = ΔH – TΔS ΔH: Change in enthalpy, the heat energy absorbed or released as reactants become products 18 Gibbs Free Energy Change § The value of ΔG is determined by changes in enthalpy and entropy. § ΔG = ΔH – TΔS ΔH: Change in enthalpy, the heat energy absorbed or released TΔS: Product of temperature (T) and entropy change (ΔS) ― Entropy is based on the number of states ― If a molecule is split from 1 -> 2 then entropy increases (positive ΔS) ― A positive ΔS makes a more negative ΔG and has higher potential energy yield 19 Gibbs Free Energy Change § The value of ΔG is determined by changes in enthalpy and entropy. § ΔG = ΔH – TΔS ΔH: Change in enthalpy, the heat energy absorbed or released TΔS: Product of temperature and entropy change § If ΔG < 0, the process has high potential energy and may go forward. § If ΔG > 0, the reaction will want to go in reverse. 20 Gibbs Free Energy Change § Under defined laboratory conditions, calculating the ΔG value of a reaction can predict how much biomass microbes will build. aerobic See any trends? anaerobic 21 Gibbs Example (ΔG = ΔH – TΔS) § Reaction: 2H2 + O2 -> 2H2O 22 Gibbs Example (ΔG = ΔH – TΔS) § Reaction: 2H2 + O2 -> 2H2O ΔH is -572 kJ/mol because the bonds of H2O are more stable and heat is released Entropy decreases (3 -> 2) so ΔS is -0.327 kJ/(mol-K) 23 Gibbs Example (ΔG = ΔH – TΔS) § Reaction: 2H2 + O2 -> 2H2O ΔH is -572 kJ/mol because the bonds of H2O are more stable and heat is released Entropy decreases (3 -> 2) so ΔS is -0.327 kJ/(mol-K) 24 Gibbs Example (ΔG = ΔH – TΔS) § Reaction: 2H2 + O2 -> 2H2O ΔH is -572 kJ/mol because the bonds of H2O are more stable and heat is released Entropy decreases (3 -> 2) so ΔS is -0.327 kJ/(mol-K) Is this a usable reaction for energy if a cell had the machinery? 25 Additivity of Energy Change is Essential 26 Additivity of Energy Change is Essential 27 Additivity of Energy Change is Essential 28 Reaction Conditions § Many factors determine ∆G: 1. Intrinsic properties ― Entropy and enthalpy 2. Environmental factors ― Concentration of reactants/products ― Temperature, pressure § “Standard” reaction conditions T = 298K (25°C), P = 1 atm, Concentrations are 1M 29 Concentrations of Reactants and Products § The concentration ratio affects ΔG. A+B⇌C+D Reactants Products 30 13.2 Energy Carriers and Electron Transfer § Many of the cell’s energy transfer reactions involve energy carriers. Molecules that gain or release small amounts of energy in reversible reactions Examples: NADH and ATP 31 13.2 Energy Carriers and Electron Transfer § Many of the cell’s energy transfer reactions involve energy carriers. Molecules that gain or release small amounts of energy in reversible reactions Examples: NADH and ATP Requires energy to generate ATP “Storage” of energy in the bonds 32 13.2 Energy Carriers and Electron Transfer § Some energy carriers also transfer electrons. Electron donor: a reducing agent (NADH giving up H) Electron acceptor: an oxidizing agent (NAD+ taking 2H+ and 2e-) 33 ATP Carries Energy § Adenosine triphosphate (ATP) contains a base (adenine), a sugar (ribose), and three phosphates. Adenine is found in DNA/RNA and can be generated § ATP is an ancient component of cells, found in all living organisms. Three-chained phosphate Adenine base Ribose sugar 34 ATP Carries Energy § Adenosine triphosphate (ATP) contains a base (adenine), a sugar (ribose), and three phosphates. Adenine is found in DNA/RNA and can be generated § ATP is an ancient component of cells, found in all living organisms. Needs to be stabilized 35 ATP Carries Energy § Under physiological conditions, ATP always forms a complex with Mg2+. Magnesium is an essential nutrient for all living cells. 36 ATP Can Transfer Energy To Cell Processes In Three Different Ways 1. Hydrolysis-releasing phosphate (Pi) 37 ATP Can Transfer Energy To Cell Processes In Three Different Ways 2. Hydrolysis-releasing pyrophosphate (PPi) 38 ATP Can Transfer Energy To Cell Processes In Three Different Ways 3. Phosphorylation of an organic molecule 39 NADH Carries Energy and Electrons § Nicotinamide adenine dinucleotide (NADH) carries two or three times as much energy as ATP. Donates and accepts electrons. Ribose ― NADH is the reduced form. ― NAD+ is the oxidized form. ADP 40 NADH Carries Energy and Electrons § Overall reduction of NAD+ consumes two hydrogen atoms to make NADH. NAD+ + 2 H+ + 2 e– → NADH + H+ ΔG°′ = 62 kJ/mol 41 FADH Carries Energy and Electrons § Flavin adenine dinucleotide (FAD) is another related coenzyme that can transfer electrons. FADH2 (reduced form) vs. FAD (oxidized form) § FAD is reduced by two electrons and two protons. 42 Why Do Different Kinds Of Reactions Use Different Energy Carriers ? § Different redox levels Food molecules vary in their number of electrons Example, lipids are more highly reduced than glucose Lipid catabolism requires more electron accepting energy carriers 43 Why Do Different Kinds Of Reactions Use Different Energy Carriers ? § Different amounts of energy Your energy yields might be enough to form NADH but not FADH2 Want to be efficient, not wasteful 44 Why Do Different Kinds Of Reactions Use Different Energy Carriers ? § Regulation and specificity Specific energy carriers can direct metabolites into different pathways serving different functions. 45 Enzymes Catalyze Metabolic Reactions § Lower the activation energy (Ea) allowing a more rapid conversion of reactants to products § Without enzymes, reactions would not occur or would run too slowly to sustain life 46 Enzymes Couple Energy-yielding With Energy-requiring Reactions Substrate binds to catalyze reaction Regulation site 47