BC351 Lecture 8 Metabolism Bioenergetics Terms Metabolism Catabolism Anabolism 1st law of Thermodynamics ATP hydrolysis Dehydrogenation Reduction potential Phosphorylated intermediate redox reactions Oxidation Reduction Reducing agent Oxidizing agent Biochemical standard free energy Actual free energy Principles 1 An introduction to metabolism 2 The conservation of energy in metabolism 3 The relationship between equilibrium free energy and standard free energy 4 The free energy available in ATP hydrolysis and the way this energy is utilized 5 REDOX reactions in carbon based systems I Metabolism Overview pgs 25 26 485 488 a What is metabolism i ii Two categories 1 Catabolism a Definition of catabolism i b Converging towards acetyl CoA 2 Anabolism a Definition of anabolism i b Diverging from acetyl CoA LN08 1 II Energy Conservation pgs 22 24 489 491 a The 1st law of Thermodynamics i What does the 1st law of thermodynamics state 1 ii One of the most fundamental aspects of bioenergetics is the conservation of energy via small successive steps in metabolic pathways b Transformation of energy in biology i Nuclear energy found in the sun Photons heat ii Plants convert photons heat to chemical energy iii This chemical energy is consumed by heterotrophs 1 Undergoes lots of different chemical conservation steps 2 These steps lead to the production of an electrochemical gradient which is then converted to mechanical energy which is used to produce ATP a These last steps will be the topics of LN 9 12 Nuclear energy Chemical energy Mechanical energy Photons heat energy Chemical energy LN08 2 c The 2nd law entropy and equilibrium pgs 491 493 i The 2nd law of thermodynamics states 1 The entropy of the universe is ALWAYS increasing ii Equilibrium remember is 1 The point in a chemical reaction where forward and reverse rates are equal AND 2 Where the free energy of the system has been minimized a At this point entropy has been maximized for the system and surroundings 3 SO According to the 2nd law of thermodynamics all chemical physical processes have a driving force to reach equilibrium BECAUSE equilibrium is where entropy of the system has been maximized iii What does this have to do with metabolism 1 Living systems have to avoid this maximal entropic state a They have to be FAR from equilibrium b How is this accomplished III Free energy pgs 491 495 a Biochemical standard free energy i Definition 1 LN08 3 2 Tells us which direction a reaction will go to reach equilibrium when starting at a standard set of conditions as defined and agreed upon by scientist ii The conditions as determined by biochemists 1 The reaction must start at a 1 1 product reactant ratio EXCEPT a pH 7 0 H 1 0 x 10 7M iii The fundamental equation demonstrating the relationship b w standard free energy change and equilibrium 1 G RTln Keq LN08 4 b Actual Free energy i Definition 1 2 It is heavily dependent on the actual products and the reactants in a biological system that are rarely if ever standard a It tells us how far a reaction is from equilibrium and which direction it will proceed to reach equilibrium at biologically relevant conditions ii The fundamental equation demonstrating the relationship b w free energy change standard free energy change and the mass action ratio 1 G G RT ln products reactants a products reactants Mass action ratio Q i This is entirely dependent upon the actual conditions prevailing in the cell 2 G G RT ln Q Pure reactant Free energy G Free energy G iii Free energy landscapes 1 1 Pure product Pure reactant Pure reactant 1 1 Pure product Free energy G product reactant Free energy G product reactant 1 1 product reactant Pure product Pure reactant LN08 5 1 1 product reactant Pure product IV Phosphoryl group transfer pgs 506 507 a ATP hydrolysis i Definition of ATP hydrolysis 1 ii The structure and breakdown products of ATP Inorganic phosphate P i Pyrophosphate PP i b Conservation of ATP free energy i Catabolic pathways conserve energy in ATP and anabolic pathways utilize energy conserved in ATP via ATP hydrolysis X ATP Y X H 2O Y G 25kJ mol ADP Pi H ATP Y X H 2O ADP X G 30 5kJ mol Y H Pi G 5 5kJ mol c How is this done i Group transfer reactions 1 In most cases the addition of Pi to a molecule will raise the molecules free energy a If the Pi is derived from ATP then the free energy that is normally released in hydrolysis is conserved LN08 6 in the phosphorylated intermediate of the reaction mechanism b Phosphorylated intermediate definition i 2 An example a The production of Gln from Glu V Redox reactions pgs 512 517 a Definition i ii Movement of electrons can be thermodynamically very favorable and can have a great capacity to do work b Reduction and oxidation LN08 7 i Start with ions 1 Fe2 Cu2 Fe3 Cu a Half reactions b Oxidation and the reducing agent i Definition of Oxidation 1 Fe2 e Fe3 ii Definition of reducing agent 1 c Reduction and the oxidizing agent Cu 2 e Cu i Definition of Reduction 1 ii Definition of Oxidizing agent 1 ii How about carbon 1 Which atoms own electrons in chemical bonds a This is directly related to the electronegativity of an atom LN08 8 b How does this then relate to metabolism i Glucose combustion C6H12O6 6O2 6H2O 6CO2 G 2840 kJ mol iii Biochemical redox reactions 1 Dehydrogenation a Definition of Dehydrogenation i b An example LN08 9 c How is free energy change quantified i The equation demonstrating free energy and its relationship with redox reactions 1 G nF E ii Reduction potentials E 1 Definition of reduction potential a b If it is large then c If it is small then 2 The change in reduction potential E a E E electron acceptor E electron donor i If it is negative ii If it is positive LN08 10 Reduced E E electron acceptor Oxidized E electron donor E 0 045 G 0 254 0 209 E 0 254 G 0 045 0 209 LN08 11