An Introduction to Metabolism 10 09 2013 Metabolism the sum total of an organism s chemical reactions Catabolic pathways involved in degradation Release energy by breaking down complex molecules to simpler compounds Anabolic pathways involved in synthesis Consume energy to build complicated molecules from simpler ones Sometimes called biosynthetic pathways Organisms transform and transfer energy Energy capacity to do work Potential Energy energy that an object possesses because of its structure or position usually chemical bond energy in biological systems Kinetic Energy relative motion of objects Energy transfers by organisms are subject to two laws of thermodynamics 1st Law of Thermodynamics principle of conservation of energy energy can be transferred and transformed but it cannot be destroyed the energy of the universe is constant 2nd Law of Thermodynamics every energy transfer or transformation makes the universe more disordered every process increases entropy With every transfer of energy some usable energy is lost as heat o Entropy S quantitative measure of disorder or randomness Free energy and spontaneous reactions Free Energy G is the portion of energy available to do work o deltaG deltaH TdeltaS o Difference between the total energy deltaH or enthalpy and the energy not available to do work TdeltaS where T is the absolute temperature and S is entropy o In a chemical reaction the energy change deltaG between the reactants and the products is the amount of useable energy that can be harvested to do work deltaG G products G reactants deltaG negative energy released and the forward reaction will occur spontaneously deltaG positive energy required and the forward reaction will not occur spontaneously o As a chemical reaction approaches equilibrium the free energy deltaG of the system decreases o When a reaction is pushed away from equilibrium the free energy deltaG of the system increases o At chemical equilibrium deltaG 0 o When deltaG 0 no work can be done Types of Chemical Reactions based on free energy changes Exergonic Fig 8 6 release energy when they occur o EX Hydrolysis of ATP Fig 8 9 High energy molecule These phosphate bonds aren t really high energy as they are often referred to The reason tat ATP is a high energy molecule is that the products ADP P have substantially lower free energy than the reactants This means that the energy difference between the products and reactants is enormous which will provide a lot of energy to do work The structure of the ATP molecule is what makes it such an efficient energy source form dictates function The 3 phosphate groups all located next to each other have negative charges like charges repel The phosphate tail is like a compressed spring When one of these bonds is broken a huge amount of energy is released Endergonic Fig 8 6 require input of energy to occur How does ATP drive work If the change in free energy deltaG for an endergonic reaction is less than the amount of energy releases by ATP hydrolysis then the 2 reactions can be coupled so that overall the reactions are exergonic o Coupled reactions energy released from exergonic reactions ATP hydrolysis is used to power endergonic reactions protein synthesis Catalysts and Enzymes Catalysts substances that speed up the rates of exergonic chemical reactions but are not themselves used up or altered Enzymes biological catalysts o Most are proteins o Highly specific for the chemicals they act on o EA activation energy Fig 8 14 and 8 15 lowers the o Doesn t alter the change in free energy between products and activation energy reactants the help of the enzyme with the substrate activity o Substrate specific a substrate is a molecule that reacts with o Active Site area of enzyme that specifically binds and reacts o A cell s chemical and physical environment affects enzyme Temperature Cofactors electron carriers that assist enzymes co enzymes vitamins Enzyme inhibitors molecules that can interact with an enzyme and make it inactive o Competitive inhibitors reduce enzymatic activity by blocking the active site Preventing substrates from entering the active sites Often resemble the substrate and compete for access to the active site Called mimics o Allosteric inhibitors do not directly compete with the substrate for access to the active site Bind a different part of the enzyme and causes a conformational change in the enzyme that affects the active site Enzyme Inhibitors Cellular Respiration and Fermentation 10 09 2013 Cellular Respiration harvesting chemical energy catabolic pathways yield energy by oxidizing organic fuels Cellular Respiration and Fermentation are catabolic pathways Fermentation is the partial degradation of sugars that occurs without the use of oxygen An anaerobic process Cellular Respiration an ATP producing pathway in which the ultimate electron acceptor is oxygen An aerobic process can live maybe 3 or 4 minutes w o ATP or oxygen C6H12O6 6O2 6CO2 6H2O Energy ATP and heat o deltaG 686 kcal mol of sugar o Respiration is the removal of energy from organic molecules and storing it in ATP Redox reactions aka Oxidation reduction reactions are exergonic reactions which involve a transfer of electrons from a less electronegative atom to a more electronegative atom An atom that receives an electron gets reduced receives a negative so the amount of positive charge gets reduced Oxidizing Agent An atom that loses an electron gets oxidized Reducing Agent Exergonic reaction potential energy gets released Na Cl Na Cl o Na becomes oxidized lost an electron Reducing Agent o Cl got reduced gains an electron Oxidizing Agent So Xe Y X Ye o X is oxidized Reducing Agent o Y is reduced Oxidizing Agent Oxidizing and reductions always go together A molecule can t be oxidized without another molecule being reduced Doesn t have to be a complete transfer if electrons from one atom to another it can involve a change in the level of electron sharing within a covalent bond o In methane CH4 C and H have similar EN s nonpolar covalent bond so the valence electrons are shared equally o When methane reacts with oxygen carbon dioxide is formed Carbon is now bonded to oxygen which is more electronegative than hydrogen So carbon has partially lost its shared electrons and has become oxidized Oxygen becomes reduced Fig 9 3 Electronegativity o Pulling an electron away from an atom requires energy The more EN an atom is the more energy is required to take an electron from it o An electron loses
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