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CAMPBELL BIOLOGY TENTH EDITION Reece • Urry • Cain • Wasserman • Minorsky • Jackson 10 Cell Respiration Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick © 2014 Pearson Education, Inc. Life Is Work § Living cells require energy from outside sources § Some animals, such as the giraffe, obtain energy by eating plants, and some animals feed on other organisms that eat plants © 2014 Pearson Education, Inc. Figure 10.1 © 2014 Pearson Education, Inc. § Energy flows into an ecosystem as sunlight and leaves as heat § Photosynthesis generates O2 and organic molecules, which are used in cellular respiration § Cells use chemical energy stored in organic molecules to generate ATP, which powers work © 2014 Pearson Education, Inc. Figure 10.2 Light energy ECOSYSTEM CO2 + H2O Photosynthesis in chloroplasts Cellular respiration in mitochondria ATP Heat energy © 2014 Pearson Education, Inc. Organic O molecules + 2 ATP powers most cellular work BioFlix: The Carbon Cycle © 2014 Pearson Education, Inc. Concept 10.1: Catabolic pathways yield energy by oxidizing organic fuels § Catabolic pathways release stored energy by breaking down complex molecules § Electron transfer plays a major role in these pathways § These processes are central to cellular respiration © 2014 Pearson Education, Inc. Catabolic Pathways and Production of ATP § The breakdown of organic molecules is exergonic § Fermentation is a partial degradation of sugars that occurs without O2 § Aerobic respiration consumes organic molecules and O2 and yields ATP § Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2 © 2014 Pearson Education, Inc. § Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration § Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat) © 2014 Pearson Education, Inc. Redox Reactions: Oxidation and Reduction § The transfer of electrons during chemical reactions releases energy stored in organic molecules § This released energy is ultimately used to synthesize ATP © 2014 Pearson Education, Inc. The Principle of Redox § Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions § In oxidation, a substance loses electrons, or is oxidized § In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced) © 2014 Pearson Education, Inc. Figure 10.UN01 becomes oxidized (loses electron) becomes reduced (gains electron) © 2014 Pearson Education, Inc. Figure 10.UN02 becomes oxidized becomes reduced © 2014 Pearson Education, Inc. § The electron donor is called the reducing agent § The electron receptor is called the oxidizing agent § Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds § An example is the reaction between methane and O2 © 2014 Pearson Education, Inc. Figure 10.3 Reactants Products becomes oxidized becomes reduced Methane (reducing agent) © 2014 Pearson Education, Inc. Oxygen (oxidizing agent) Carbon dioxide Water Oxidation of Organic Fuel Molecules During Cellular Respiration § During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced © 2014 Pearson Education, Inc. Figure 10.UN03 becomes oxidized becomes reduced © 2014 Pearson Education, Inc. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain § In cellular respiration, glucose and other organic molecules are broken down in a series of steps § Electrons from organic compounds are usually first transferred to NAD+, a coenzyme § As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration § Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP © 2014 Pearson Education, Inc. Figure 10.4 2 e− + 2 H+ NAD+ 2 e− + H+ Dehydrogenase NADH H+ Reduction of NAD+ 2[H] (from food) Oxidation of NADH Nicotinamide (oxidized form) © 2014 Pearson Education, Inc. H+ Nicotinamide (reduced form) Figure 10.4a NAD+ Nicotinamide (oxidized form) © 2014 Pearson Education, Inc. Figure 10.4b 2 e− + 2 H+ 2 e− + H+ Dehydrogenase NADH H+ Reduction of NAD+ 2[H] (from food) Oxidation of NADH H+ Nicotinamide (reduced form) © 2014 Pearson Education, Inc. Figure 10.UN04 Dehydrogenase © 2014 Pearson Education, Inc. § NADH passes the electrons to the electron transport chain § Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction § O2 pulls electrons down the chain in an energyyielding tumble § The energy yielded is used to regenerate ATP © 2014 Pearson Education, Inc. Figure 10.5 H2 + ½ O2 2H Free energy, G rt spo tran tron n chai Explosive release Controlled release of energy Elec Free energy, G 2 H+ + 2 e− ½ O2 + ATP ATP ATP 2 e− ½ O2 2 H+ H 2O (a) Uncontrolled reaction © 2014 Pearson Education, Inc. H 2O (b) Cellular respiration The Stages of Cellular Respiration: A Preview § Harvesting of energy from glucose has three stages § Glycolysis (breaks down glucose into two molecules of pyruvate) § The citric acid cycle (completes the breakdown of glucose) § Oxidative phosphorylation (accounts for most of the ATP synthesis) © 2014 Pearson Education, Inc. Figure 10.UN05 1. GLYCOLYSIS (color-coded blue throughout the chapter) 2. PYRUVATE OXIDATION and the CITRIC ACID CYCLE (color-coded orange) 3. OXIDATIVE PHOSPHORYLATION: Electron transport and chemiosmosis (color-coded purple) © 2014 Pearson Education, Inc. Figure 10.6-1 Electrons via NADH GLYCOLYSIS Glucose Pyruvate CYTOSOL ATP Substrate-level © 2014 Pearson Education, Inc. MITOCHONDRION Figure 10.6-2 Electrons via NADH GLYCOLYSIS Glucose Electrons via NADH and FADH2 PYRUVATE OXIDATION CITRIC ACID CYCLE Pyruvate Acetyl CoA CYTOSOL MITOCHONDRION ATP ATP Substrate-level Substrate-level © 2014 Pearson Education, Inc. Figure 10.6-3 Electrons via NADH GLYCOLYSIS Glucose Electrons via NADH and FADH2 PYRUVATE OXIDATION CITRIC ACID CYCLE Pyruvate Acetyl CoA CYTOSOL MITOCHONDRION ATP ATP Substrate-level Substrate-level © 2014 Pearson Education, Inc. OXIDATIVE PHOSPHORYLATION (Electron transport and chemiosmosis) ATP Oxidative BioFlix: Cellular Respiration © 2014 Pearson Education, Inc. § The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions © 2014 Pearson Education, Inc. § Oxidative phosphorylation accounts for almost 100% of the ATP generated by cellular respiration § A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation § For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of ATP © 2014 Pearson Education, Inc. Figure 10.7 Enzyme Enzyme ADP P ATP Substrate Product © 2014 Pearson Education, Inc. Concept 10.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate § Glycolysis (“sugar splitting”) breaks down glucose into two molecules of pyruvate § Glycolysis occurs in the cytoplasm and has two major phases § Energy investment phase § Energy payoff phase § Glycolysis occurs whether or not O2 is present © 2014 Pearson Education, Inc. Figure 10.UN06 GLYCOLYSIS ATP © 2014 Pearson Education, Inc. PYRUVATE OXIDATION CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION Figure 10.8 Energy Investment Phase Glucose 2 ATP used 2 ADP + 2 P Energy Payoff Phase 4 ADP + 4 P 2 NAD+ + 4 e− + 4 H+ 4 ATP formed 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net Glucose 4 ATP formed − 2 ATP used 2 NAD+ + 4 e− + 4 H+ © 2014 Pearson Education, Inc. 2 Pyruvate + 2 H2O 2 ATP 2 NADH + 2 H+ Figure 10.9a GLYCOLYSIS: Energy Investment Phase Glyceraldehyde 3-phosphate (G3P) Glucose ATP ADP Fructose ATP 6-phosphate ADP Glucose 6-phosphate Fructose 1,6-bisphosphate Isomerase Hexokinase 1 © 2014 Pearson Education, Inc. Phosphoglucoisomerase Phosphofructokinase 2 3 Aldolase 4 5 Dihydroxyacetone phosphate (DHAP) Figure 10.9aa-1 GLYCOLYSIS: Energy Investment Phase Glucose © 2014 Pearson Education, Inc. Figure 10.9aa-2 GLYCOLYSIS: Energy Investment Phase Glucose Glucose 6-phosphate ATP ADP Hexokinase 1 © 2014 Pearson Education, Inc. Figure 10.9aa-3 GLYCOLYSIS: Energy Investment Phase Glucose Glucose 6-phosphate ATP ADP Hexokinase 1 © 2014 Pearson Education, Inc. Fructose 6-phosphate Phosphoglucoisomerase 2 Figure 10.9ab-1 GLYCOLYSIS: Energy Investment Phase Fructose 6-phosphate © 2014 Pearson Education, Inc. Figure 10.9ab-2 GLYCOLYSIS: Energy Investment Phase Fructose ATP 6-phosphate ADP Phosphofructokinase 3 © 2014 Pearson Education, Inc. Fructose 1,6-bisphosphate Figure 10.9ab-3 GLYCOLYSIS: Energy Investment Phase Glyceraldehyde 3-phosphate (G3P) Fructose ATP 6-phosphate ADP Fructose 1,6-bisphosphate Isomerase Phosphofructokinase 3 © 2014 Pearson Education, Inc. Aldolase 4 5 Dihydroxyacetone phosphate (DHAP) Figure 10.9b GLYCOLYSIS: Energy Payoff Phase 2 NADH + 2 NAD + 2 H+ 2 Triose phosphate 2 dehydrogenase Glyceraldehyde 3-phosphate (G3P) 6 © 2014 Pearson Education, Inc. 2 ATP 2 ADP 2 2 Phosphoglycerokinase Phosphoglyceromutase 1,3-Bisphosphoglycerate 7 3-Phosphoglycerate 8 2-Phosphoglycerate 2 H 2O 2 Enolase 10 2 ATP 2 ADP 2 Pyruvate kinase 10 Phosphoenolpyruvate (PEP) Pyruvate Figure 10.9ba-1 GLYCOLYSIS: Energy Payoff Phase Glyceraldehyde 3-phosphate (G3P) Isomerase 5 Aldolase 4 Dihydroxyacetone phosphate (DHAP) © 2014 Pearson Education, Inc. Figure 10.9ba-2 GLYCOLYSIS: Energy Payoff Phase Glyceraldehyde 3-phosphate (G3P) Aldolase 4 Isomerase Triose phosphate 2 dehydrogenase 5 6 Dihydroxyacetone phosphate (DHAP) © 2014 Pearson Education, Inc. 2 NADH 2 NAD+ 2 H+ 2 1,3-Bisphosphoglycerate Figure 10.9ba-3 GLYCOLYSIS: Energy Payoff Phase Glyceraldehyde 3-phosphate (G3P) Aldolase 4 Isomerase Triose phosphate 2 dehydrogenase 5 6 Dihydroxyacetone phosphate (DHAP) © 2014 Pearson Education, Inc. 2 NADH 2 NAD+ 2 H+ 2 2 ATP 2 ADP 2 Phosphoglycerokinase 1,3-Bisphosphoglycerate 7 3-Phosphoglycerate Figure 10.9bb-1 GLYCOLYSIS: Energy Payoff Phase 2 3-Phosphoglycerate © 2014 Pearson Education, Inc. Figure 10.9bb-2 GLYCOLYSIS: Energy Payoff Phase 2 2 Phosphoglyceromutase 3-Phosphoglycerate © 2014 Pearson Education, Inc. 8 2-Phosphoglycerate 2 H 2O 2 Enolase 10 Phosphoenolpyruvate (PEP) Figure 10.9bb-3 GLYCOLYSIS: Energy Payoff Phase 2 2 Phosphoglyceromutase 3-Phosphoglycerate © 2014 Pearson Education, Inc. 8 2-Phosphoglycerate 2 H 2O 2 Enolase 10 2 ATP 2 ADP 2 Pyruvate kinase 10 Phosphoenolpyruvate (PEP) Pyruvate Concept 10.3: After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules § In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed © 2014 Pearson Education, Inc. Oxidation of Pyruvate to Acetyl CoA § Before the citric acid cycle can begin, pyruvate must be converted to acetyl Coenzyme A (acetyl CoA), which links glycolysis to the citric acid cycle § This step is carried out by a multienzyme complex that catalyses three reactions © 2014 Pearson Education, Inc. Figure 10.UN07 GLYCOLYSIS © 2014 Pearson Education, Inc. PYRUVATE OXIDATION CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION Figure 10.10 MITOCHONDRION CYTOSOL CO2 Coenzyme A 3 1 2 Pyruvate Transport protein © 2014 Pearson Education, Inc. NAD+ NADH + H+ Acetyl CoA The Citric Acid Cycle § The citric acid cycle, also called the Krebs cycle, completes the break down of pyruvate to CO2 § The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn © 2014 Pearson Education, Inc. Figure 10.11 PYRUVATE OXIDATION Pyruvate (from glycolysis, 2 molecules per glucose) CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA CoA CITRIC ACID CYCLE FADH2 2 CO2 3 NAD+ CoA FAD 3 NADH + 3 H+ ADP + P i ATP © 2014 Pearson Education, Inc. Figure 10.11a PYRUVATE OXIDATION Pyruvate (from glycolysis, 2 molecules per glucose) CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA © 2014 Pearson Education, Inc. Figure 10.11b Acetyl CoA CoA CoA CITRIC ACID CYCLE FADH2 2 CO2 3 NAD+ 3 NADH FAD + 3 H+ ADP + P i ATP © 2014 Pearson Education, Inc. § The citric acid cycle has eight steps, each catalyzed by a specific enzyme § The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate § The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle § The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain © 2014 Pearson Education, Inc. Figure 10.UN08 GLYCOLYSIS PYRUVATE OXIDATION CITRIC ACID CYCLE ATP © 2014 Pearson Education, Inc. OXIDATIVE PHOSPHORYLATION Figure 10.12-1 Acetyl CoA CoA-SH 1 Oxaloacetate Citrate CITRIC ACID CYCLE © 2014 Pearson Education, Inc. Figure 10.12-2 Acetyl CoA CoA-SH H 2O 1 Oxaloacetate 2 Citrate CITRIC ACID CYCLE © 2014 Pearson Education, Inc. Isocitrate Figure 10.12-3 Acetyl CoA CoA-SH H 2O 1 Oxaloacetate 2 Citrate CITRIC ACID CYCLE Isocitrate NAD+ 3 NADH + H+ CO2 α-Ketoglutarate © 2014 Pearson Education, Inc. Figure 10.12-4 Acetyl CoA CoA-SH H 2O 1 Oxaloacetate 2 Citrate Isocitrate NAD+ CITRIC ACID CYCLE NADH + H+ 3 CO2 CoA-SH 4 NAD+ NADH Succinyl CoA © 2014 Pearson Education, Inc. + H+ α-Ketoglutarate CO2 Figure 10.12-5 Acetyl CoA CoA-SH H 2O 1 Oxaloacetate 2 Citrate Isocitrate NAD+ CITRIC ACID CYCLE NADH + H+ 3 CO2 CoA-SH 4 α-Ketoglutarate CoA-SH 5 Succinate Pi GTP GDP ADP ATP © 2014 Pearson Education, Inc. NAD+ Succinyl CoA NADH + H+ CO2 Figure 10.12-6 Acetyl CoA CoA-SH H 2O 1 Oxaloacetate 2 Citrate Isocitrate NAD+ CITRIC ACID CYCLE Fumarate CO2 CoA-SH 4 6 α-Ketoglutarate CoA-SH 5 FADH2 NAD+ FAD Succinate Pi GTP GDP ADP ATP © 2014 Pearson Education, Inc. NADH + H+ 3 Succinyl CoA NADH + H+ CO2 Figure 10.12-7 Acetyl CoA CoA-SH H 2O 1 Oxaloacetate 2 Malate H 2O Citrate NAD+ CITRIC ACID CYCLE 7 Fumarate NADH + H+ 3 CO2 CoA-SH 4 6 α-Ketoglutarate CoA-SH 5 FADH2 NAD+ FAD Succinate Pi GTP GDP ADP ATP © 2014 Pearson Education, Inc. Isocitrate Succinyl CoA NADH + H+ CO2 Figure 10.12-8 Acetyl CoA CoA-SH NADH + H+ H 2O 1 NAD+ Oxaloacetate 8 2 Malate H 2O Citrate NAD+ CITRIC ACID CYCLE 7 Fumarate NADH + H+ 3 CO2 CoA-SH 4 6 α-Ketoglutarate CoA-SH 5 FADH2 NAD+ FAD Succinate Pi GTP GDP ADP ATP © 2014 Pearson Education, Inc. Isocitrate Succinyl CoA NADH + H+ CO2 Figure 10.12a Acetyl CoA CoA-SH H 2O 1 Oxaloacetate 2 Citrate © 2014 Pearson Education, Inc. Isocitrate Figure 10.12b Isocitrate NAD+ NADH + H+ 3 CO2 CoA-SH 4 NAD+ © 2014 Pearson Education, Inc. Succinyl CoA NADH + H+ α-Ketoglutarate CO2 Figure 10.12c Fumarate 6 CoA-SH FADH2 5 FAD Pi Succinate GTP GDP ADP ATP © 2014 Pearson Education, Inc. Succinyl CoA Figure 10.12d NADH + H+ NAD+ 8 Oxaloacetate Malate H 2O 7 Fumarate © 2014 Pearson Education, Inc. Concept 10.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis § Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food § These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation © 2014 Pearson Education, Inc. The Pathway of Electron Transport § The electron transport chain is in the inner membrane (cristae) of the mitochondrion § Most of the chain’s components are proteins, which exist in multiprotein complexes § The carriers alternate reduced and oxidized states as they accept and donate electrons § Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O © 2014 Pearson Education, Inc. Figure 10.UN010 GLYCOLYSIS PYRUVATE OXIDATION CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION ATP © 2014 Pearson Education, Inc. Figure 10.13 NADH Free energy (G) relative to O2 (kcal/mol) 50 2 e− NAD+ FADH2 40 FMN 2 e− FAD Fe•S II I Fe•S Multiprotein complexes Q III Cyt b 30 Fe•S Cyt c1 IV Cyt c Cyt a 20 10 0 Cyt a3 2 e− (originally from NADH or FADH2) 2 H+ + ½ O2 H 2O © 2014 Pearson Education, Inc. Figure 10.13a Free energy (G) relative to O2 (kcal/mol) NADH © 2014 Pearson Education, Inc. 50 2 e− NAD+ FADH2 40 FMN 2 e− FAD Fe•S II I Fe•S Q III Cyt b 30 Multiprotein complexes Fe•S Cyt c1 IV Cyt c Cyt a 20 10 Cyt a3 2 e− Free energy (G) relative to O2 (kcal/mol) Figure 10.13b © 2014 Pearson Education, Inc. 30 Cyt c1 IV Cyt c Cyt a 20 10 0 Cyt a3 2 e− (originally from NADH or FADH2) 2 H+ + ½ O2 H 2O § Electrons are transferred from NADH or FADH2 to the electron transport chain § Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2 § The electron transport chain generates no ATP directly § It breaks the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts © 2014 Pearson Education, Inc. Chemiosmosis: The Energy-Coupling Mechanism § Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space § H+ then moves back across the membrane, passing through the protein complex, ATP synthase § ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP § This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work © 2014 Pearson Education, Inc. Figure 10.14 INTERMEMBRANE H+ SPACE Rotor Stator Internal rod Catalytic knob ADP + Pi MITOCHONDRIAL MATRIX © 2014 Pearson Education, Inc. ATP Video: ATP Synthase 3-D Structure, Top View © 2014 Pearson Education, Inc. Video: ATP Synthase 3-D Structure, Side View © 2014 Pearson Education, Inc. Figure 10.15 Protein complex of electron carriers H+ ATP synthase H+ H+ H+ Cyt c IV Q III I II FADH2 FAD NADH (carrying electrons from food) 2 H+ + ½ O2 NAD+ H 2O ADP + P i H+ 1 Electron transport chain Oxidative phosphorylation © 2014 Pearson Education, Inc. ATP 2 Chemiosmosis Figure 10.15a Protein complex of electron carriers H+ H+ Cyt c IV Q III I II FADH2 FAD NADH (carrying electrons from food) © 2014 Pearson Education, Inc. H+ 2 H+ + ½ O2 NAD+ 1 Electron transport chain H 2O Figure 10.15b H+ ADP + P i ATP synthase ATP H+ 2 Chemiosmosis © 2014 Pearson Education, Inc. § The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis § The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work © 2014 Pearson Education, Inc. An Accounting of ATP Production by Cellular Respiration § During cellular respiration, most energy flows in this sequence: glucose → NADH → electron transport chain → proton-motive force → ATP § About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 32 ATP § There are several reasons why the number of ATP is not known exactly © 2014 Pearson Education, Inc. Figure 10.16 Electron shuttles span membrane CYTOSOL 2 NADH 2 Pyruvate PYRUVATE OXIDATION 2 Acetyl CoA + 2 ATP Maximum per glucose: © 2014 Pearson Education, Inc. 6 NADH 2 NADH GLYCOLYSIS Glucose MITOCHONDRION 2 NADH or 2 FADH2 2 FADH2 CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron transport and chemiosmosis) + 2 ATP + about 26 or 28 ATP About 30 or 32 ATP Figure 10.16a Electron shuttles span membrane 2 NADH GLYCOLYSIS Glucose 2 Pyruvate + 2 ATP © 2014 Pearson Education, Inc. 2 NADH or 2 FADH2 Figure 10.16b 6 NADH 2 NADH PYRUVATE OXIDATION 2 Acetyl CoA CITRIC ACID CYCLE + 2 ATP © 2014 Pearson Education, Inc. 2 FADH2 Figure 10.16c 2 NADH or 2 FADH2 2 NADH 6 NADH 2 FADH2 OXIDATIVE PHOSPHORYLATION (Electron transport and chemiosmosis) + about 26 or 28 ATP © 2014 Pearson Education, Inc. Figure 10.16d Maximum per glucose: © 2014 Pearson Education, Inc. About 30 or 32 ATP Concept 10.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen § Most cellular respiration requires O2 to produce ATP § Without O2, the electron transport chain will cease to operate § In that case, glycolysis couples with anaerobic respiration or fermentation to produce ATP © 2014 Pearson Education, Inc. § Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O2, for example sulfate § Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP © 2014 Pearson Education, Inc. Types of Fermentation § Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis § Two common types are alcohol fermentation and lactic acid fermentation © 2014 Pearson Education, Inc. § In alcohol fermentation, pyruvate is converted to ethanol in two steps § The first step releases CO2 § The second step produces ethanol § Alcohol fermentation by yeast is used in brewing, winemaking, and baking © 2014 Pearson Education, Inc. Figure 10.17 2 ADP + 2 P i 2 ATP 2 ADP + 2 P i GLYCOLYSIS Glucose Glucose 2 ATP GLYCOLYSIS 2 Pyruvate 2 NAD+ 2 Ethanol (a) Alcohol fermentation © 2014 Pearson Education, Inc. 2 NADH + 2 H+ 2 CO2 2 Acetaldehyde 2 NAD+ 2 NADH + 2 H+ 2 Lactate (b) Lactic acid fermentation 2 Pyruvate Figure 10.17a 2 ADP + 2 P i Glucose 2 ATP GLYCOLYSIS 2 Pyruvate 2 NAD+ 2 NADH + 2 H+ 2 Ethanol (a) Alcohol fermentation © 2014 Pearson Education, Inc. 2 CO2 2 Acetaldehyde Figure 10.17b 2 ADP + 2 P i Glucose 2 ATP GLYCOLYSIS 2 NAD+ 2 NADH + 2 H+ 2 Lactate (b) Lactic acid fermentation © 2014 Pearson Education, Inc. 2 Pyruvate Animation: Fermentation Overview © 2014 Pearson Education, Inc. § In lactic acid fermentation, pyruvate is reduced by NADH, forming lactate as an end product, with no release of CO2 § Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt § Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce © 2014 Pearson Education, Inc. Comparing Fermentation with Anaerobic and Aerobic Respiration § All use glycolysis (net ATP = 2) to oxidize glucose and harvest chemical energy of food § In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis © 2014 Pearson Education, Inc. § The processes have different mechanisms for oxidizing NADH: § In fermentation, an organic molecule (such as pyruvate or acetaldehyde) acts as a final electron acceptor § In cellular respiration electrons are transferred to the electron transport chain § Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule © 2014 Pearson Education, Inc. § Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2 § Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration § In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes © 2014 Pearson Education, Inc. Figure 10.18 Glucose CYTOSOL Glycolysis Pyruvate No O2 present: Fermentation O2 present: Aerobic cellular respiration MITOCHONDRION Ethanol, lactate, or other products © 2014 Pearson Education, Inc. Acetyl CoA CITRIC ACID CYCLE The Evolutionary Significance of Glycolysis § Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere § Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP § Glycolysis is a very ancient process © 2014 Pearson Education, Inc. Concept 10.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways § Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways © 2014 Pearson Education, Inc. The Versatility of Catabolism § Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration § Glycolysis accepts a wide range of carbohydrates § Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle © 2014 Pearson Education, Inc. § Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) § Fatty acids are broken down by beta oxidation and yield acetyl CoA § An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate © 2014 Pearson Education, Inc. Figure 10.19-1 Proteins Carbohydrates Amino acids Sugars © 2014 Pearson Education, Inc. Fats Glycerol Fatty acids Figure 10.19-2 Proteins Carbohydrates Amino acids Sugars Fats Glycerol GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 © 2014 Pearson Education, Inc. Pyruvate Fatty acids Figure 10.19-3 Proteins Carbohydrates Amino acids Sugars Fats Glycerol GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA © 2014 Pearson Education, Inc. Fatty acids Figure 10.19-4 Proteins Carbohydrates Amino acids Sugars Fats Glycerol GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA CITRIC ACID CYCLE © 2014 Pearson Education, Inc. Fatty acids Figure 10.19-5 Proteins Carbohydrates Amino acids Sugars Fats Glycerol Fatty acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA CITRIC ACID CYCLE © 2014 Pearson Education, Inc. OXIDATIVE PHOSPHORYLATION Biosynthesis (Anabolic Pathways) § The body uses small molecules to build other substances § These small molecules may come directly from food, from glycolysis, or from the citric acid cycle © 2014 Pearson Education, Inc. Regulation of Cellular Respiration via Feedback Mechanisms § Feedback inhibition is the most common mechanism for metabolic control § If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down § Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway © 2014 Pearson Education, Inc. Figure 10.20 Glucose GLYCOLYSIS Fructose 6-phosphate AMP Stimulates Phosphofructokinase Inhibits Fructose 1,6-bisphosphate Inhibits Pyruvate ATP Citrate Acetyl CoA CITRIC ACID CYCLE Oxidative phosphorylation © 2014 Pearson Education, Inc. Figure 10.UN10a © 2014 Pearson Education, Inc. Figure 10.UN10b © 2014 Pearson Education, Inc. Figure 10.UN11 Outputs Inputs GLYCOLYSIS Glucose © 2014 Pearson Education, Inc. 2 Pyruvate + 2 ATP + 2 NADH Figure 10.UN12 Inputs 2 Pyruvate 2 Acetyl CoA 2 Oxaloacetate © 2014 Pearson Education, Inc. Outputs CITRIC ACID CYCLE 2 ATP 8 NADH 6 CO2 2 FADH2 Figure 10.UN13 H+ H+ IV Q III I II FADH2 FAD NAD+ (carrying electrons from food) © 2014 Pearson Education, Inc. H+ Cyt c Protein complex of electron carriers NADH INTERMEMBRANE SPACE 2 H+ + ½ O2 MITOCHONDRIAL MATRIX H 2O Figure 10.UN14 INTERMEMBRANE SPACE H+ MITOCHONDRIAL MATRIX ADP + P i © 2014 Pearson Education, Inc. ATP synthase H+ ATP Phosphofructokinase activity Figure 10.UN15 Low ATP concentration High ATP concentration Fructose 6-phosphate concentration © 2014 Pearson Education, Inc. pH difference across membrane Figure 10.UN16 Time © 2014 Pearson Education, Inc. Figure 10.UN17 © 2014 Pearson Education, Inc.