Chapter 9

Chapter 9 - 1/6 Chapter 9: Cellular Respiration catabolic...

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1/6 Chapter 9: Cellular Respiration catabolic pathway: releases stored energy by breaking down complex molecules exergonic reaction releases energy, endergonic absorbs energy organic compounds possess potential energy as a result of their arrangement of atoms with the help of enzymes, a cell systematically degrades complex molecules rich in potential energy to simpler waste products that have less energy (which can be used to do work, the rest is dissipated in heat) fermentation: no oxygen, aerobic respiration: oxygen consumed as a reactant along with organic fuel C6H12O2 + 6O2 6CO2 + 6H2O + Energy (ATP + heat) Breakdown of glucose is exergonic (G: -686 kcal/mol) o Negative G means products store less energy than the reactants o Reaction happens spontaneously When oxygen becomes H2O, it is reduced because the electrons of the covalent bonds spend more time near the oxygen (not a direct transfer of electrons; still shared) Oxygen is one of the most potent of all oxidizing agents because it is so electronegative An electron loses potential energy when it moves from a less electronegative atom to a more electronegative one 6H12O2 (oxidized) + 6O2 (reduced) 6CO2 + 6H2O Electrons lose potential energy and energy is released Organic molecules with an abundance of hydrogen are excellent fuels because energy can be released as electrons fall down energy gradient when transferred to oxygen Energy state of the electron changes as hydrogen is transferred to oxygen (in respiration the oxidation of glucose transfers electrons to a lower energy state, liberating energy for ATP synthesis) Only the barrier of activation energy holds back the flood of electrons to a lower energy state
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2/6 Energy cannot be released from a fuel all at once because that would be inefficient, so glucose and other organic fuels are broken down in a series of steps each catalyzed by an enzyme Each electron travels with a proton (hydrogen atom) Hydrogen atoms are passed first to the electron carrier NAD+ o Enzymes called dehydrogenases remove a pair of hydrogen atoms from the substrate (2 e and 2 H), oxidizing it o The enzyme delivers the 2 electrons along with one proton (the other proton is released as a H+ ion into the surrounding solution) to NAD+, NAD+ becomes NADH Electron Transport Chain o Difference between the mixing of H2 and O2 for energy (Explosive reaction) vs. cell respiration: 1) Hydrogen that reacts with oxygen is derived from organic molecules
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This note was uploaded on 09/28/2010 for the course BISC 220 taught by Professor Mcclure during the Spring '09 term at USC.

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Chapter 9 - 1/6 Chapter 9: Cellular Respiration catabolic...

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