Test 3 Review I Chapter 9 162 182 a Catabolic Pathways yield energy by oxidizing organic fuels i Catabolic pathway metabolic pathways that release stored energy by breaking down complex molecules ii Organic compounds possess potential energy bc of the arrangement of electrons in the bonds b w their atoms iii Compounds that can participate in exergonic reactions can act as fuel iv Fermentation catabolic partial degradation of sugars or other organic fuel that occurs without the use of oxygen v Aerobic respiration catabolic most efficient oxygen is consumed as a reactant along with the organic fuel 1 Cells of most prokaryotic and eukaryotic organisms can carry out aerobic respiration vi Anaerobic respiration when prokaryotes use substances other than oxygen as reactants in a similar process that harvests chemical energy without oxygen vii Cellular respiration includes both aerobic and anaerobic processes but mostly refers to aerobic breathing in oxygen viii Overall process of respiration 1 Organic compounds Oxygen CO2 Water Energy ix Steps of cellular respiration by tracking degradation of glucose 1 C6H12O6 6O2 6CO2 6H2O Energy ATP Heat 2 Breakdown is exergonic a G 686 kcal mol i Spontaneous x ATP needed as a chemical drive shaft in catabolism xi Redox reactions 1 Oxidation the loss of electrons a Oxidizing agent 2 Reduction gaining electrons a Reducing agent electron donor 3 Oxidation and reduction always go hand in hand 4 Not all involve complete transfer of electrons from one substance to another some change the degree of electron sharing in covalent bonds a Ex Methane Combustion i When methane reacts with oxygen forming carbon dioxide electrons end up shared less equally between the carbon atom and its new covalent partners the oxygen atoms which are very electronegative In effect the carbon atom has partially lost its shared electrons thus methane has been oxidized ii The O2 molecule reacts with hydrogen forming water the from methane electrons of the covalent bonds spend more time near oxygen The oxygen molecules have gained electrons so it is reduced xii Energy must be added to pull electrons away from an atom 1 The more electronegative the atom the more energy required xiii Energy yielding redox process 1 Respiration a Oxidation of glucose and other molecules in food xiv C6H12O6 6O2 6CO2 6H2O Energy 1 Glucose becomes oxidized 6CO2 2 Oxygen becomes reduced 6H2O 3 Electrons lose potential energy along the way and energy is released 4 Hydrogen is transferred from glucose to oxygen xv In respiration the oxidation of glucose transfers electrons to a lower energy state liberating energy that becomes available for ATP synthesis xvi Stepwise Energy Harvest via NAD and the Electron Transport Chain 1 Hydrogen atoms are passed through the coenzyme electron carrier NAD can cycle easily between NAD and NADH 2 NAD acts as an oxidizing agent in respiration a Enzymes called dehydrogenases make it possible for NAD to trap electrons from glucose and the other organic molecules in food by removing a pair of hydrogen atoms 2e and 2p from the substrate oxidizing it b The enzyme delivers the 2 electrons along with 1 proton to its coenzyme NAD 3 When NAD receives these 2 electrons and one proton it becomes reduced to NADH a NADH molecules represent stored energy b This stored energy can be used to make ATP when the electrons complete their fall down energy gradient from NADH to oxygen 4 There is an electron transport chain which helps break the fall of electrons to oxygen into several energy releasing steps xvii The Stages of Cellular Respiration 1 Glycolysis a Electron transport chain consists of a number of molecules mostly proteins built into the inner membrane of the mitochondria of eukaryotic cells 5 Electrons removed by glucose by NADH to the top high energy end of the chain with O2 at the bottom low energy end capturing these electrons along with hydrogen nuclei H forming water 6 Exergonic reaction G 53 kcal mol 222 kj mol 7 Oxygen pulls electrons down the chain in an energy yielding tumble analogous to gravity pulling objects downhill 8 Downhill route a glucose NADH electron transport chain O2 a Occurs in cytosol b Begins the degradation process by breaking glucose into two molecules of a compound called pyruvate i In eukaryotes pyruvate enters the mitochondrion and is oxidized to a compound called acetyl CoA 2 Pyruvate Oxidation and the Citric Acid Cycle a The breakdown of glucose to carbon dioxide b Redox NAD to NADH 3 Oxidative Phosphorylation Electron transport and chemiosmosis a Takes place in the inner membrane of mitochondrion b The electron transport chain accepts electrons from the breakdown products of the first two stages and passes these electrons from one molecule to another c At the end of the chain the electrons are combined with molecular oxygen and hydrogen ions H forming water d Oxidative Phosphorylation Energy released at each step is stored in a form the mitochondrion can use to make ATP from ADP 90 of ATP generated by respiration e Substrate level phosphorylation a mode of ATP synthesis that occurs when an enzyme transfers a phosphate group from a substrate molecule to ADP xviii 1 glucose molecule 686 kcal mol generates 32 ATP molecules each with 7 3 kcal mol b Glycolysis harvests chemical energy by oxidizing glucose to pyruvate i Glycolysis sugar splitting ii Glucose a six carbon sugar is split into 2 three carbon sugars iii These sugars are oxidized to form 2 molecules of pyruvate iv Glycolysis phases 1 Energy investment phase a Spends ATP 2 Energy payoff phase produced a ATP invested is paid off with interest when ATP is substrate level phosphorylation and NAD is reduced to NADH by electrons released during the oxidation of glucose after v Net energy yield for glycolysis per glucose molecule 2 ATP 2 NADH vi No carbon released as CO2 c After Pyruvate is oxidized the citric acid cycle completes the energy yielding oxidation of organic molecules i Upon entering mitochondrion pyruvate is converted to coenzyme acetyl CoA 1 This step linking glycolysis and the citric acid cycle is carried out by a multi enzyme complex that catalyzes three reactions a Pyruvates carboxyl group COO is removed and given off as a molecule of CO2 b The remaining two carbon fragment is oxidized forming acetate CH3COO The extracted electrons are transferred to NAD storing energy in the form of NADH c Coenzyme A CoA is attached via its sulfur atom to the acetate forming acetyl CoA which has a
View Full Document
Unlocking...