Chapter 9 Oxidation and Reduction Oxidation Removal of electrons Reduction Adding of electrons Reducing Agent Electron Donor Oxidizing Agent Electron Acceptor Oxidation of organic molecules Lead to lose of C H or C C covalent bonds oxidation of glucose releases energy from ATP Exergonic Delta G Spontaneous Reduction or organic molecules Lead to gain of C H or C C covalent bonds Endergonic Delta G Nonspontaneous Concept 9 1 Catabolic pathways yield energy by oxidizing organic fuels Several processes are central to cellular respiration and related pathways Breakdown of organic molecules is exergonic Fermentation Partial degradation of sugars that occurs without oxygen Aerobic respiration consumes organic molecules and oxygen Anaerobic Respiration is similar to aerobic respiration but consumes Cellular respiration both anaerobic and aerobic often refers to aerobic everything but oxygen Redox Reactions Release energy is used to synthesize ATP Assembled from ADP P using free energy from oxidation of glucose Oxidation of organic fuel during cellular respiration Fuel Glucose is oxidized and oxygen is reduced Carbon Dioxide is produced from oxidation of glucose and not reduction of oxygen NAD Electrons from organic compounds are usually first transferred to NAD Nicotinamide Adenine Dinucleotide Is an electron acceptor NAD functions as an oxidizing agent during cellular respiration NADH passes the electrons to the electron transport chain Passes in a series of steps instead of one explosive step Stages of Cellular respiration Harvesting Energy from Glucose 1 Glycolysis Breaks down glucose into two molecules of pyruvate 2 Citric Acid Cycle Completes breakdown of glucose 3 Oxidative Phosphorylation Accounts for most of ATP synthesis about 90 32 molecules Smaller amount of ATP is harvested from glycolysis and citric acid cycle by substrate level phosphorylation Concept 9 2 Glycolysis major phases Splitting of sugar into two molecules of pyruvate Glycolysis occurs with or without oxygen in cytoplasm and has two 1 Energy Investment phase a 2 ATP One by Hexokinase another by Phosphofructokinase 2 Energy Payoff Phase a 4 ATP made Two by phosphoglycerokinase and another 2 by pyruvatekinase Partial oxidation of glucose forms 2 pyruvic acid molecules Loss of C H Electrons removed from glucose by oxidation are added to the electron carrier NAD 2 NAD are reduced to 2 NADH Energy releases by partial oxidation of glucose converts 2ADP to 2 ATP Results of Glycolysis and C C bonds molecules Summary 1 2 pyruvate molecules 2H2O Molecules 2 2 ATP Molecules 3 2NAD NADH Concept 9 3 After pyruvate is oxidized the citric acid cycle completes the energy yielding oxidation of organic molecules In the presence of oxygen pyruvate enters the mitochondria where oxidation of glucose is complete Oxidation of pyruvate to Acetyl CoA Before the citric cycle begins pyruvate must be converted to acetyl CoA which links glycolysis to the citric acid cycle A multienzyme complex that catalyzes three reactions carries out this step One pyruvate molecules is used to produce Acetyl CoA the byproduct of the process include 1 NADH HCNA NAD is reduced 2 CO2 Citric Acid Cycle of pyruvate to carbon dioxide The citric acid cycle also called the Krebs cycle completes the break down Takes place within the mitochondrial matrix The cycle oxidizes organic fuel derived from pyruvate secreting 1 ATP 3NADH and 1 FADH2 per turn Partial oxidation breaks C C bonds and releases CO2 Electrons from oxidation of pyruvic acid are added to NAD and FAD to form NADH and FADH2 respectively 1 ATP is assembled from ADP PO4 from energy released by oxidation Since 1 molecule of glucose produces 2 molecules of pyruvic acid 2 Acetyl CoA molecules enter the cycle and produces 2 ATP 6 NADH and 2 FADH2 and 4 CO2 per turn Citric Acid cycle has 8 steps each catalyzed by a specific enzyme The Acetyl group of Acetyl CoA begins the cycle by combining with Next seven steps decompose the citrate back to oxaloacetate making the The NADH and FADH2 produced by the cycle relay electrons extracted oxaloacetate forming citrate process a cycle from food to the electron transport The Pathway of Electron Transport Electron Transport Chain ETC is in the inner membrane Cristae of the Most of the chains components are proteins which exist in multiprotein The carriers alternated reduced and oxidized states as they accept and mitochondria complexes donate electrons Electrons drop in free energy as they go down the chain and are finally passed to oxygen forming a water molecule Electrons are transferred from NADH from stage 2 and electron shuttled form stage 1 or FADH2 From stage 2 to the electron transport chain each with an iron atom to oxygen Electrons are passed through a number of proteins including cytochromes The ETC generates no ATP directly Chains function is to break the large free energy drop from good to oxygen into smaller steps that release manageable amounts of energy Chemiosmosis The Energy Coupling Mechanism Electrons transfer on the ETC causes proteins to Pump H from the mitochondrial matrix to the intermembrane space This concentrates H in the intermembrane space H then moves back across the membrane passing through the protein ATP synthase the phosphorylation of 26 28 ATP drive cellular work ATP synthase uses the exergonic flow of H in the matrix to drive This is an example of chemiosmosis the use of energy in a H gradient to The energy stored in a H gradient across membrane couples the redox reactions of the ETC to ATP synthesis H gradient is referred to as a proton motive force emphasizing its capacity to do work acid cycle produced H2O At the end of the ETC FAD and NAD are reformed reused in the citric Electrons leaving at the end of the ETC are added to 2H and O2 to This is why oxygen is needed to be the final electron acceptor An accounting of ATP production by cellular respiration During cellular respiration most energy flows in this sequence Glucose NADH ETC Proton motive force ATP 34 of the energy in a glucose molecule is transferred to ATP during cellular respiration making 30 32 ATP 2 from Stage 1 2 from stage 2 26 28 atom stage 3 Versatility of Catabolism into cellular respiration Catabolic pathways funnel electrons from many kinds of organic molecules Glycolysis accepts a wide range of carbohydrates Proteins must be digested to amino acids amino groups can feed glycolysis or the citric acid cycle ammonia urea and other waste products Deamination of the
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