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What do you know about Cellular Respiration? What do you know about Cellular Respiration? Shuttling Energy Sources Across a Membrane! • Different steps occur in different locations of a cell! • Resources need to be moved across the mitochondrial membrane What do you know about Cell Respiration? Energy Flow in the Ecosystem Light energy ECOSYSTEM CO2 H2O Photosynthesis in chloroplasts Organic O 2 molecules Cellular respiration in mitochondria ATP Heat energy ATP powers most cellular work Energy is generated by Catabolic pathways involved in oxidizing organic fuels Catabolic Pathways and ATP Production The breakdown of organic molecules is exergonic Fermentation partial sugar degradation without O2 Aerobic respiration consumes organic molecules and O2 and yields ATP Cellular Respiration AKA Aerobic Respiration = REQUIRES O2 to complete! C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat) -ΔG: -686kcal/mol 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 The Principle of Redox: Transfer of Electrons! becomes oxidized (loses electron) becomes reduced (gains electron) •In oxidation, a substance loses electrons, or is oxidized (becomes more positive) •In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced) More Redox! becomes oxidized becomes reduced Electron donor is called the reducing agent Loses Electrons Oxidized (LEO) Electron receptor is called the oxidizing agent Gains Electrons Reduced (GER) Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds Redox of Methane and Oxygen Gas Reactants Products becomes oxidized Energy becomes reduced Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water Oxidation of Organic Fuel Molecules During Cellular Respiration Fuel (such as glucose) is oxidized, and O2 is reduced becomes oxidized becomes reduced In general lots of C-H bonds make a great fuel source Carbs: Why Are They Good Energy? Electrons are transferred in the form of H atoms. C-H bonds are higher in energy. The more C-H bonds the more energy! C6H12O6 O2 CO2 Loses Electrons H2O Gains Electrons H is transferred from C to O, a lower energy state releases energy for ATP formation Redox in Respiration Occur in Steps Enzymes control release of energy by H transfer at key steps! Not directly to O, but to coenzyme to make more energy first! Nicotinamide Adenine Dinucleotide (NAD) and the Energy Harvesting NAD NADH Dehydrogenase Reduction of NAD (from food) Nicotinamide (oxidized form) Oxidation of NADH Nicotinamide (reduced form) •Electrons from organic compounds are usually first transferred to NAD+, a coenzyme •Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP Electron Removal From Glucose Sugar-source NADH Dehydrogenase Sugar-source NAD+ Released into the surrounding solution Energy Production in the Electron Transport Chain H2 1/2 O2 2H 1/ Explosive release of heat and light energy Free energy, G Free energy, G (from food via NADH) Controlled release of + 2H 2e energy for synthesis of ATP O2 ATP ATP ATP 2 e 2 1/ H+ H2O (a) Uncontrolled reaction 2 H2O (b) Cellular respiration 2 O2 The Stages of Cellular Respiration: A Preview 1. Glycolysis (color-coded teal) glucose to pyruvate 2. Pyruvate oxidation and the citric acid cycle (color-coded salmon) completes glucose breakdown 3. Oxidative phosphorylation: electron transport and chemiosmosis (color-coded violet) Most ATP synthesis Glycolysis Electrons carried via NADH Glycolysis Glucose Pyruvate MITOCHONDRION CYTOSOL ATP Substrate-level phosphorylation Figure 9.6-2 Electrons carried via NADH and FADH2 Electrons carried via NADH Glycolysis Glucose Pyruvate CYTOSOL Pyruvate oxidation Acetyl CoA Citric acid cycle MITOCHONDRION ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Figure 9.6-3 Electrons carried via NADH and FADH2 Electrons carried via NADH Glycolysis Glucose Pyruvate CYTOSOL Pyruvate oxidation Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation BioFlix: Cellular Respiration © 2011 Pearson Education, Inc. Substrate-level Phosphorylation Enzyme Enzyme ADP P Substrate ATP Product A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation Oxidative Phosphorylation The sum of all the energyreleasing steps in the mitochondria accounts for almost 90% of the ATP generated Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Energy Phases of Glycolysis Energy Investment Phase Glucose 2 ADP 2 P 2 phases: Energy investment Energy Payoff 2 ATP used Energy Payoff Phase 4 ADP 4 P No Carbon released! 2 NAD+ 4 e 4 H+ 4 ATP formed 2 NADH 2 H+ 2 Pyruvate 2 H2O Does not depend on oxygen! Net Glucose 4 ATP formed 2 ATP used 2 NAD+ 4 e 4 H+ 2 Pyruvate 2 H2O 2 ATP 2 NADH 2 H+ Figure 9.9-1 Glycolysis: Energy Investment Phase Glucose ATP Glucose 6-phosphate ADP Hexokinase 1 Figure 9.9-2 Glycolysis: Energy Investment Phase Glucose ATP Glucose 6-phosphate Fructose 6-phosphate ADP Hexokinase 1 Phosphoglucoisomerase 2 Figure 9.9-3 Glycolysis: Energy Investment Phase Glucose ATP Glucose 6-phosphate Fructose 6-phosphate ATP ADP ADP Hexokinase 1 Fructose 1,6-bisphosphate Phosphoglucoisomerase Phosphofructokinase 2 3 Figure 9.9-4 Glycolysis: Energy Investment Phase Glucose ATP Glucose 6-phosphate Fructose 6-phosphate ATP ADP ADP Hexokinase 1 Fructose 1,6-bisphosphate Phosphoglucoisomerase Phosphofructokinase 2 3 Aldolase Dihydroxyacetone phosphate 4 Glyceraldehyde 3-phosphate Isomerase 5 To step 6 Figure 9.9-5 Glycolysis: Energy Payoff Phase 2 NADH 2 NAD Triose phosphate dehydrogenase 6 + 2 H 2Pi 1,3-Bisphosphoglycerate Figure 9.9-6 Glycolysis: Energy Payoff Phase 2 ATP 2 NADH 2 NAD Triose phosphate dehydrogenase 6 + 2 H 2 ADP 2 Phosphoglycerokinase 2Pi 1,3-Bisphosphoglycerate 7 3-Phosphoglycerate Figure 9.9-7 Glycolysis: Energy Payoff Phase 2 ATP 2 NADH 2 NAD Triose phosphate dehydrogenase 6 + 2 H 2 ADP 2 2 Phosphoglyceromutase Phosphoglycerokinase 2Pi 1,3-Bisphosphoglycerate 7 3-Phosphoglycerate 8 2-Phosphoglycerate Figure 9.9-8 Glycolysis: Energy Payoff Phase 2 ATP 2 H2O 2 NADH 2 NAD Triose phosphate dehydrogenase 6 +2 H 2 ADP 2 2 1,3-Bisphosphoglycerate 7 Enolase Phosphoglyceromutase Phosphoglycerokinase 2Pi 2 9 3-Phosphoglycerate 8 2-Phosphoglycerate Phosphoenolpyruvate (PEP) Figure 9.9-9 Glycolysis: Energy Payoff Phase 2 ATP 2 ATP 2 H2O 2 NADH 2 NAD Triose phosphate dehydrogenase 6 + 2 H 2 ADP 2 2 1,3-Bisphosphoglycerate 7 Enolase Phosphoglyceromutase Phosphoglycerokinase 2Pi 9 3-Phosphoglycerate 8 2 ADP 2 2-Phosphoglycerate Pyruvate kinase Phosphoenolpyruvate (PEP) 10 Pyruvate Glycolysis Glycolysis: Energy Investment Phase Glucose ATP Fructose 6-phosphate Glucose 6-phosphate ADP Hexokinase 1 Adds a phosphate = energizing the glucose Phosphoglucoisomerase 2 Isomerizes the sugar! Glycolysis Glycolysis: Energy Investment Phase Fructose 6-phosphate ATP Fructose 1,6-bisphosphate ADP Cuts the sugar in half! Phosphofructokinase 3 Second energy investment Aldolase Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate Isomerase Switches the 3C sugar between 2 forms 4 5 To step 6 Glycolysis Glycolysis: Energy Payoff Phase 2 ATP 2 NADH + 2 H 2 NAD 2 ADP 2 2 Triose phosphate dehydrogenase 6 Phosphoglycerokinase 2Pi 1,3-Bisphosphoglycerate Removes 2 H to make an NADH and H+ 7 3-Phosphoglycerate Removes a phosphate to make ATP! Glycolysis Glycolysis: Energy Payoff Phase 2 H2O 2 2 Shuffles the phosphate to a different carbon 8 2 ADP 2 Phosphoglyceromutase 3-Phosphoglycerate 2 ATP Enolase 2-Phosphoglycerate 9 Pulls off water 2 Pyruvate kinase Phosphoenolpyruvate (PEP) 10 Pyruvate Makes more ATP Citric acid cycle completes the energy-yielding oxidation of organic molecules Oxidation of Pyruvate to Acetyl CoA MITOCHONDRION CYTOSOL CO2 Coenzyme A 3 1 2 Pyruvate NAD NADH + H Acetyl CoA Transport protein This step is carried out by a multienzyme complex that catalyses three reactions to bring pyruvate into the mitochondria Lose: 1 CO2 per pyruvate Gain: 1 NADH per pyruvate The Citric Acid Cycle Pyruvate CO2 NAD CoA NADH 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 REMEMBER 2 pyruvate per Glucose! + H Acetyl CoA CoA CoA Citric acid cycle 2 CO2 3 NAD FADH2 3 NADH FAD + 3 H ADP + P i ATP Overview: Citric Acid Cycle • 8 steps, each catalyzed by a specific enzyme • Acetyl combines with oxaloacetatecitrate • The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle Acetyl CoA CoA-SH 1 Oxaloacetate Citrate Citric acid cycle Acetyl CoA CoA-SH H2O 1 Oxaloacetate 2 Citrate Isocitrate Citric acid cycle Acetyl CoA CoA-SH H2O 1 Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle 3 NADH + H CO2 -Ketoglutarate Acetyl CoA CoA-SH H2O 1 Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 CoA-SH -Ketoglutarate 4 NAD NADH Succinyl CoA + H CO2 Acetyl CoA CoA-SH H2O 1 Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 CoA-SH -Ketoglutarate 4 CoA-SH 5 NAD Succinate GTP GDP ADP ATP Pi Succinyl CoA NADH + H CO2 Acetyl CoA CoA-SH H2O 1 Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle Fumarate NADH 3 + H CO2 CoA-SH -Ketoglutarate 4 6 CoA-SH 5 FADH2 NAD FAD Succinate GTP GDP ADP ATP Pi Succinyl CoA NADH + H CO2 Acetyl CoA CoA-SH H2O 1 Oxaloacetate 2 Malate Citrate Isocitrate NAD Citric acid cycle 7 H2O Fumarate NADH 3 + H CO2 CoA-SH -Ketoglutarate 4 6 CoA-SH 5 FADH2 NAD FAD Succinate GTP GDP ADP ATP Pi Succinyl CoA NADH + H CO2 Acetyl CoA CoA-SH NADH + H H2O 1 NAD 8 Oxaloacetate 2 Malate Citrate Isocitrate NAD Citric acid cycle 7 H2O Fumarate NADH 3 + H CO2 CoA-SH -Ketoglutarate 4 6 CoA-SH 5 FADH2 NAD FAD Succinate GTP GDP ADP ATP Pi Succinyl CoA NADH + H CO2 Acetyl group (What’s left of the pyruvate) combines with Oxaloacetate to make Citrate Acetyl CoA CoA-SH H 2O 1 Citrate is isomerized by removing water and then adding it back Oxaloacetate 2 Citrate Isocitrate Isocitrate is oxidized (Loses 2 H) and reduces NAD+ A second reaction occurs, removing CO2 Isocitrate NAD NADH 3 + H CO2 CoA-SH -Ketoglutarate 4 NAD NADH Succinyl CoA + H CO2 More CO2 is lost, and another NAD+ is reduced. Coenzyme A makes another appearance A phosphate group replaces CoA. The Phosphate is then transferred to GDP to make GTP Fumarate 6 CoA-SH 5 FADH2 FAD Succinate Succinate is oxidized by FAD to make FADH2 GTP GDP ADP ATP Pi Succinyl CoA NADH + H Another redox to make NADH and oxaloacetate NAD 8 Oxaloacetate Malate H 2O Water molecule added to rearrange bonds 7 Fumarate During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis The Pathway of Electron Transport Occurs 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 50 2 e NAD FADH2 2 e Free energy (G) relative to O2 (kcal/mol) NADH 40 FMN FeS FeS II Q III Cyt b 30 Multiprotein complexes FAD I FeS Cyt c1 IV Cyt c Cyt a 20 10 0 Cyt a3 2 e (originally from NADH or FADH2) 2 H + 1/2 O2 H2O NADH and FADH2 Bring electrons to the ETC Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2 no ATP directly generated Release energy in small steps Oxidative Phosphorylation and the ETC H H H Protein complex of electron carriers Cyt c Q I IV III II FADH2 FAD NADH H 2 H + 1/2O2 ATP synthase H2O NAD ADP P i (carrying electrons from food) ATP H 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation Electron transfer is coupled with H+ pumping into intermembrane space of mitchondria Chemiosmosis: Energy-Coupling Mechanism Using H+ Gradient to do Work INTERMEMBRANE SPACE H Stator Rotor The H+ gradient is referred to as a proton-motive force H+ then moves back across the membrane, passing through the proton, ATP synthase ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP H+ generated by ETC coupled with ATP synthesis! Internal rod Catalytic knob ADP + Pi ATP MITOCHONDRIAL MATRIX 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 32-36 ATP There are several reasons why the number of ATP is not known exactly Figure 9.16 Electron shuttles span membrane 2 NADH Glycolysis 2 Pyruvate Glucose MITOCHONDRION 2 NADH or 2 FADH2 2 NADH Pyruvate oxidation 2 Acetyl CoA 2 ATP Maximum per glucose: CYTOSOL 6 NADH 2 FADH2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis 2 ATP about 26 or 28 ATP About 30 or 32 ATP Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen Anaerobic Respiration Oxygen is not used or may be poisonous! Certain fungi and bacteria undergo Glycolysis coupled to an electron transport chain but use other molecules as final electron acceptors like sulfate! Fermentation: Anaerobic Respiration Using Substrate Level Phosphorylation Fermentation consists of glycolysis plus reactions that regenerate NAD+ Without NAD+ Glycolysis couldn’t happen Animation: Fermentation Overview Right-click slide / select “Play” © 2011 Pearson Education, Inc. Fermentation 2 ADP 2 P Glucose i 2 ADP 2 P 2 ATP Glycolysis Glucose i 2 ATP Glycolysis 2 Pyruvate 2 NAD 2 Ethanol (a) Alcohol fermentation 2 NADH 2 H 2 NAD 2 CO2 2 Acetaldehyde 2 NADH 2 H 2 Pyruvate 2 Lactate (b) Lactic acid fermentation In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2 In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate with no release of CO2 Figure 9.17a 2 ADP 2 P i Glucose 2 ATP Glycolysis 2 Pyruvate 2 NAD 2 Ethanol (a) Alcohol fermentation 2 NADH 2 H 2 CO2 2 Acetaldehyde 2 ADP 2 P i Glucose 2 ATP Glycolysis 2 NADH 2 H 2 NAD 2 Pyruvate 2 Lactate (b) Lactic acid fermentation Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt, and human muscles when O2 is scarce Importance of Pyruvate Glucose CYTOSOL Glycolysis Pyruvate Obligate anaerobes – Oxygen is poisonous! Facultative anaerobes – can go either way No O2 present: Fermentation O2 present: Aerobic cellular respiration MITOCHONDRION Ethanol, lactate, or other products Acetyl CoA Citric acid cycle Glycolysis and the citric acid cycle connect to many other metabolic pathways Catabolism of Various Food Sources Proteins Carbohydrates Amino acids Sugars Glycolysis Glycolysis accepts a wide range of carbohydrates Glucose Glyceraldehyde 3- P 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 NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation Fats Glycerol Fatty acids 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 Glucose Feedback Mechanisms and Cell Respiration AMP Glycolysis Fructose 6-phosphate •Feedback inhibition is the most common mechanism for control •If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down Stimulates Phosphofructokinase Fructose 1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA Citric acid cycle Oxidative phosphorylation Fermentation vs. Anaerobic vs. 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 The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule Figure 9.UN06 Inputs Outputs Glycolysis Glucose 2 Pyruvate 2 ATP 2 NADH Figure 9.UN07 Outputs Inputs 2 Pyruvate 2 Acetyl CoA 2 Oxaloacetate Citric acid cycle 2 ATP 8 NADH 6 CO2 2 FADH2 Figure 9.UN08 H INTERMEMBRANE SPACE H H Cyt c Protein complex of electron carriers IV Q III I II FADH2 FAD NAD NADH (carrying electrons from food) 2 H + 1/2 O2 MITOCHONDRIAL MATRIX H2O Figure 9.UN09 INTERMEMBRANE SPACE H ATP synthase MITOCHONDRIAL MATRIX ADP + P i H ATP pH difference across membrane Figure 9.UN10 Time Figure 9.UN11