Campbell Biology Chapter 9: Cellular Respiration and Fermentation PDF

Chapter 9 Cellular Respiration and Fermentation Lecture Presentations by Nicole Tunbridge and © 2017 Pearson Edu...

Chapter 9 Cellular Respiration and Fermentation Lecture Presentations by Nicole Tunbridge and © 2017 Pearson Education, Inc. Kathleen Fitzpatrick Life Is Work ▪ Living cells require energy from outside sources to do work ▪ The work of the cell includes assembling polymers, membrane transport, moving, and reproducing ▪ Animals can obtain energy to do this work by feeding on other animals or photosynthetic organisms ▪ The outside source of energy is food, and the energy stored in the organic molecules of food ultimately comes from the sun © 2017 Pearson Education, Inc. Figure 9.1 © 2017 Pearson Education, Inc. ▪ Energy flows into an ecosystem as sunlight, and leaves as heat. ▪ The chemical elements essential to life are recycled ▪ 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 © 2017 Pearson Education, Inc. Figure 9.2 Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic CO2 + H2O + O2 molecules Cellular respiration in mitochondria ATP powers ATP most cellular work Heat energy © 2017 Pearson Education, Inc. BioFlix: The Carbon Cycle © 2017 Pearson Education, Inc. Concept 9.1: 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. © 2017 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 © 2017 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) © 2017 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 © 2017 Pearson Education, Inc. The Principle of Redox ▪ How do the catabolic pathways that decompose glucose and other organic fuels yield energy? ▪ the transfer of electrons during the chemical reactions. ▪ The relocation of electrons releases energy stored in organic molecules, and this energy ultimately is used to synthesize ATP © 2017 Pearson Education, Inc. Figure 9.UN01 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) becomes oxidized (loses electron) becomes reduced (gains electron) © 2017 Pearson Education, Inc. Figure 9.UN02 becomes oxidized becomes reduced © 2017 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 © 2017 Pearson Education, Inc. Figure 9.3 Reactants Products becomes oxidized Energy becomes reduced Methane Oxygen Carbon dioxide Water (reducing (oxidizing agent) agent) © 2017 Pearson Education, Inc. Oxidation of Organic Fuel Molecules During Cellular Respiration ▪ During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced ▪ Organic molecules with an abundance of hydrogen are excellent sources of high-energy electrons ▪ Energy is released as the electrons associated with hydrogen ions are transferred to oxygen, a lower energy state ▪ in general, we see fuels with multiple C¬ H bonds oxidized into products with multiple C¬ O bonds. © 2017 Pearson Education, Inc. Figure 9.UN03 becomes oxidized becomes reduced © 2017 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 © 2017 Pearson Education, Inc. Figure 9.4 NAD+ NADH Dehydrogenase Reduction of NAD+ 2[H] (from food) Oxidation of NADH Nicotinamide Nicotinamide (oxidized form) (reduced form) © 2017 Pearson Education, Inc. Figure 9.UN04 Dehydrogenase © 2017 Pearson Education, Inc. ▪ NADH passes the electrons to the electron transport chain. ▪ The electron transport chain passes electrons in a series of steps instead of one explosive reaction. ▪ O2 pulls electrons down the chain in an energy- yielding tumble. ▪ The energy yielded is used to regenerate ATP. © 2017 Pearson Education, Inc. The Stages of Cellular Respiration: A Preview ▪ Harvesting of energy from glucose has three stages 1. Glycolysis (breaks down glucose into two molecules of pyruvate) 2. The citric acid cycle (completes the breakdown of glucose) 3. Oxidative phosphorylation (accounts for most of the ATP synthesis) © 2017 Pearson Education, Inc. Figure 9.6_3 Electrons Electrons via NADH via NADH and FADH2 GLYCOLYSIS PYRUVATE OXIDATIVE OXIDATION CITRIC PHOSPHORYLATION ACID Glucose Pyruvate Acetyl CoA CYCLE (Electron transport and chemiosmosis) CYTOSOL MITOCHONDRION ATP ATP ATP Substrate-level Substrate-level Oxidative © 2017 Pearson Education, Inc. BioFlix: Cellular Respiration © 2017 Pearson Education, Inc. ▪ The process that generates almost 90% of the ATP is called oxidative phosphorylation ▪ A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation Enzyme Enzyme ADP P ATP Substrate Product © 2017 Pearson Education, Inc. ▪ For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of ATP © 2017 Pearson Education, Inc. Concept 9.2: 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 © 2017 Pearson Education, Inc. Figure 9.UN06 CITRIC OXIDATIVE PYRUVATE GLYCOLYSIS ACID PHOSPHORYL- OXIDATION CYCLE ATION ATP © 2017 Pearson Education, Inc. Figure 9.8 Energy Investment Phase Glucose 2 ATP used 2 ADP + 2 P Energy Payoff Phase 4 ADP + 4 P 4 ATP formed 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net Glucose 2 Pyruvate + 2 H2O 4 ATP formed – 2 ATP used 2 ATP 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+ © 2017 Pearson Education, Inc. Figure 9.9a GLYCOLYSIS: Energy Investment Phase Glyceraldehyde 3-phosphate (G3P) ATP Glucose Fructose ATP Fructose Glucose 6-phosphate 6-phosphate 1,6-bisphosphate ADP ADP Isomerase 5 Hexokinase Phosphogluco- Phospho- Aldolase Dihydroxyacetone isomerase fructokinase 1 4 phosphate (DHAP) 2 3 © 2017 Pearson Education, Inc. Figure 9.9b GLYCOLYSIS: Energy Payoff Phase 2 ATP 2 ATP 2 NADH 2 H2O 2 ADP 2 NAD+ + 2 H+ 2 ADP 2 2 2 2 2 Triose Phospho- Phospho- Enolase Pyruvate phosphate 2 P glycerokinase glyceromutase kinase Glycer- dehydrogenase i 9 aldehyde 1,3-Bisphospho- 7 3-Phospho- 8 2-Phospho- Phosphoenol- 10 Pyruvate 6 3-phosphate glycerate glycerate glycerate pyruvate (PEP) (G3P) © 2017 Pearson Education, Inc. Concept 9.3: After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules ▪ In the presence of O2, pyruvate enters a mitochondrion (in eukaryotic cells), where the oxidation of glucose is completed © 2017 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 catalyzes three reactions 1. Oxidation of pyruvate and release of CO2 2. Reduction of NAD+ to NADH 3. Combination of the remaining two-carbon fragment and coenzyme A to form acetyl CoA © 2017 Pearson Education, Inc. Figure 9.UN07 CITRIC OXIDATIVE PYRUVATE GLYCOLYSIS ACID PHOSPHORYL- OXIDATION CYCLE ATION © 2017 Pearson Education, Inc. Figure 9.10 MITOCHONDRION CYTOSOL Coenzyme A CO2 1 3 2 NAD+ NADH + H+ Acetyl CoA Pyruvate Transport protein © 2017 Pearson Education, Inc. The Citric Acid Cycle ▪ The citric acid cycle, also called the Krebs cycle, completes the breakdown of pyruvate to CO2 ▪ The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn © 2017 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 © 2017 Pearson Education, Inc. Figure 9.UN08 CITRIC OXIDATIVE PYRUVATE GLYCOLYSIS ACID PHOSPHORYL- OXIDATION CYCLE ATION ATP © 2017 Pearson Education, Inc. Figure 9.11 PYRUVATE OXIDATION Pyruvate (from glycolysis, 2 molecules per glucose) CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA NADH + H+ CoA NAD+ CITRIC ACID 2 CO2 CYCLE FADH2 2 NAD+ FAD 2 NADH + 2 H+ ADP + P i ATP © 2017 Pearson Education, Inc. Concept 9.4: 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 © 2017 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 ▪ Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O ▪ Electron carriers alternate between reduced and oxidized states as they accept and donate electrons © 2017 Pearson Education, Inc. ▪ 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 © 2017 Pearson Education, Inc. Figure 9.UN09 CITRIC OXIDATIVE PYRUVATE GLYCOLYSIS ACID PHOSPHORYL- OXIDATION CYCLE ATION ATP © 2017 Pearson Education, Inc. Figure 9.13 NADH (least electronegative) 50 2 e– NAD+ Complexes I-IV FADH2 each consist of 2 e– FAD multiple proteins Free energy (G) relative to O2 (kcal/mol) 40 FMN I with electron Fe S Fe S II carriers. Q III Cyt b 30 Fe S Cyt c1 IV Cyt c Cyt a Electron transport Cyt a3 20 chain 10 2 e– 2 H+ + ½ O2 0 (most electronegative) H2O © 2017 Pearson Education, Inc. Chemiosmosis: The Energy-Coupling Mechanism ▪ ATP synthase uses the energy of an existing ion gradient to power ATP synthesis. The power source for ATP synthase is a difference in the concentration of H+ (a pH difference) on opposite sides of the inner mitochondrial membrane. ▪ H+ then moves down its concentration gradient back across the membrane, passing through the protein complex ATP synthase © 2017 Pearson Education, Inc. ▪ H+ moves into binding sites on the rotor of ATP synthase, causing it to spin in a way that catalyzes phosphorylation of ADP to ATP ▪ This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work © 2017 Pearson Education, Inc. Figure 9.14 H+ Stator INTERMEMBRANE SPACE Rotor Internal rod Catalytic knob ADP + Pi ATP MITOCHONDRIAL MATRIX © 2017 Pearson Education, Inc. Video: ATP Synthase 3-D Structure, Top View © 2017 Pearson Education, Inc. Video: ATP Synthase 3-D Structure, Side View © 2017 Pearson Education, Inc. ▪ Certain electron carriers in the electron transport chain accept and release H+ along with the electrons ▪ In this way, 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 © 2017 Pearson Education, Inc. Figure 9.15 H+ ATP Protein H+ H+ synthase complex H+ of electron Cyt c carriers IV Q I III II 2 H+ + ½ O2 H2O FADH2 FAD NADH NAD+ ADP + P i ATP (carrying electrons from food) H+ 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation © 2017 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 ▪ The rest of the energy is lost as heat © 2017 Pearson Education, Inc. Figure 9.16 Electron shuttles MITOCHONDRION span membrane 2 NADH or CYTOSOL 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 GLYCOLYSIS PYRUVATE OXIDATIVE OXIDATION CITRIC PHOSPHORYLATION ACID Glucose 2 Pyruvate 2 Acetyl CoA (Electron transport CYCLE and chemiosmosis) + 2 ATP + 2 ATP + about 26 or 28 ATP About Maximum per glucose: 30 or 32 ATP © 2017 Pearson Education, Inc. Concept 9.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen ▪ Most cellular respiration depends on electronegative oxygen to pull electrons down the transport chain ▪ Without oxygen, the electron transport chain will cease to operate ▪ In that case, glycolysis couples with anaerobic respiration or fermentation to produce ATP © 2017 Pearson Education, Inc. ▪ Anaerobic respiration uses an electron transport chain with a final electron acceptor other than oxygen, for example, sulfate ▪ Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP © 2017 Pearson Education, Inc. Types of Fermentation ▪ Two common types are alcohol fermentation and lactic acid fermentation ▪ alcohol fermentation ▪ lactic acid fermentation © 2017 Pearson Education, Inc. ▪ In alcohol fermentation, pyruvate is converted to ethanol in two steps ▪ The first step releases CO2 from pyruvate ▪ The second step produces NAD+ and ethanol ▪ Alcohol fermentation by yeast is used in brewing, winemaking, and baking © 2017 Pearson Education, Inc. Figure 9.17a 2 ADP + 2 P i 2 ATP Glucose GLYCOLYSIS 2 Pyruvate 2 NAD+ 2 NADH 2 CO2 + 2 H+ NAD+ REGENERATION 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation © 2017 Pearson Education, Inc. ▪ In lactic acid fermentation, pyruvate is reduced by NADH, forming NAD+ and lactate as end products, 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 during strenuous exercise when O2 is scarce © 2017 Pearson Education, Inc. Figure 9.17b 2 ADP + 2 P i 2 ATP Glucose GLYCOLYSIS 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate NAD+ REGENERATION 2 Lactate (b) Lactic acid fermentation © 2017 Pearson Education, Inc. Animation: Fermentation Overview © 2017 Pearson Education, Inc. Comparing Fermentation with Anaerobic and Aerobic Respiration ▪ All use glycolysis (net ATP = 2) to oxidize glucose and harvest the chemical energy of food ▪ In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis © 2017 Pearson Education, Inc. ▪ The processes have different mechanisms for oxidizing NADH to NAD+: ▪ 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 © 2017 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 © 2017 Pearson Education, Inc. Figure 9.18 Glucose Glycolysis CYTOSOL Pyruvate No O2 present: O2 present: Fermentation Aerobic cellular respiration MITOCHONDRION Ethanol, Acetyl CoA lactate, or other products CITRIC ACID CYCLE © 2017 Pearson Education, Inc. Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways ▪ Glycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways © 2017 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 including starch, glycogen, and several disaccharides ▪ Proteins that are used for fuel must be digested to amino acids and their amino groups must be removed © 2017 Pearson Education, Inc. ▪ Fats are digested to glycerol (used to produce compounds needed for glycolysis) and fatty acids ▪ Fatty acids are broken down by beta oxidation and yield acetyl CoA, NADH, and FADH2 ▪ An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate © 2017 Pearson Education, Inc. Figure 9.19_5 Proteins Carbohydrates Fats Amino Sugars Glycerol Fatty acids acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Acetyl CoA CITRIC ACID OXIDATIVE CYCLE PHOSPHORYLATION © 2017 Pearson Education, Inc. Biosynthesis (Anabolic Pathways) ▪ The body uses small molecules from food to build other their own molecules such as proteins ▪ These small molecules may come directly from food, from glycolysis, or from the citric acid cycle © 2017 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 © 2017 Pearson Education, Inc. Figure 9.20 Glucose AMP GLYCOLYSIS Fructose 6-phosphate Stimulates + Phosphofructokinase – – Fructose 1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA CITRIC ACID CYCLE Oxidative phosphorylation © 2017 Pearson Education, Inc. Figure 9.UN11 Inputs Outputs GLYCOLYSIS Glucose 2 Pyruvate 2 ATP 2 NADH © 2017 Pearson Education, Inc. Figure 9.UN12 Inputs Outputs 2 Pyruvate 2 Acetyl CoA 2 ATP 8 NADH CITRIC 2 Oxaloacetate ACID CYCLE 6 CO2 2 FADH2 © 2017 Pearson Education, Inc. Figure 9.UN13 INTERMEMBRANE H+ H+ SPACE Protein H+ complex Cyt c of electron carriers IV Q III I II 2 H+ + ½ O2 H2O FADH2 FAD NADH NAD+ MITOCHONDRIAL MATRIX (carrying electrons from food) © 2017 Pearson Education, Inc. Figure 9.UN14 INTER- MEMBRANE SPACE H+ MITO- CHONDRIAL MATRIX ATP synthase ADP + P i H+ ATP © 2017 Pearson Education, Inc.