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Figure 7.2 Get used to this picture…. Light energy ECOSYSTEM CO2 H2O Photosynthesis in chloroplasts Cellular respiration in mitochondria ATP Heat energy © 2014 Pearson Education, Inc. Organic O2 molecules ATP powers most cellular work Key points you need to take away from this unit 1. Mitochondria • Mitochondria have a double membrane that allows compartmentalization within the mitochondria and is important to its function • The outer membrane is smooth, but the inner membrane is highly convoluted, forming folds called cristae • Cristae contain enzymes important to ATP production; cristae also increase the surface area for ATP production © 2014 Pearson Education, Inc. Key points you need to take away from this unit 1. Glycolysis/Citric Acid Cycle • Glycolysis rearranges the bonds in glucose molecules, releasing free energy to form ATP from ADP and inorganic phosphate, and resulting in the production of pyruvate • Pyruvate is transported from the cytoplasm to the mitochondrion, where further oxidation occurs. • In the Krebs cycle, CO2 is released from organic intermediates ATP is synthesized from ADP and inorganic phosphate via substrate level phosphorylation and electrons are captured by coenzymes • Electrons that are extracted in the series of Krebs cycle reaction are carried by NADH and FADH2 to the electron transport chain © 2014 Pearson Education, Inc. Key points you need to take away from this unit 1.Oxidative phosphorylation • • • • • Electron transport chain reactions occur in chloroplasts, mitochondria, and prokaryotic plasma membranes In cellular respiration, electrons delivered by NADH and FADH2 are passed to a series of electron acceptors as they move toward the terminal electron acceptor, oxygen. The passage of e- is accompanied by the formation of a H+ gradient across the inner mitochondrial membrane, with the membrane separating a region of high [H+] from a region of low [H+]. In prokaryotes, the passage of e- is accompanied by the outward movement of H+ across the plasma membrane The flow of H+ back through the membrane-bound ATP synthase by chemiosmosis generaties ATP from ADP and inorganic phosphate. In cellular respiration, decoupling oxidative phosphorylation from e- transport is involved with thermoregulation © 2014 Pearson Education, Inc. Where we started….. • Energy flows through nature in the form of chemical energy, which is stored in bonds, especially C-C, C-H • Mitochondria are the site of energy production in eukaryotic cells • Compounds can be oxidized or reduced, in respiration, fuels (glucose) are oxidized while O2 is reduced • Respiration has three main steps: Glycolysis, Citric Acid Cyle, and Oxidative Phosphorylation (ETC) © 2014 Pearson Education, Inc. From last time….. • Glycolysis is the breakdown of glucose, takes place in the cytoplasm, and occurs whether or not O2 is available • There are 2 phases of glycolysis: energy investment, energy payoff • It takes 2 ATP to get glycolysis going, but the pathway yields 4 ATP, leading to a net of 2 ATP • NAD+ is reduced to NADH which shuttles e- to the ETC • Pyruvate enters the mitochondria by diffusion through channel proteins, and is oxidized into CO2 and acetyl-CoA which is used in the Citric Acid cycle Ready? © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. Figure 7.10 Pyruvate CYTOSOL (from glycolysis, 2 molecules per glucose) • The citric acid cycle, also called the Krebs cycle, completes the breakdown of pyruvate to CO2 CO2 NAD CoA NADH H Acetyl CoA MITOCHONDRION CoA • The cycle oxidizes organic fuel derived from pyruvate, generating: – 1 ATP – 3 NADH – 1 FADH2 per turn, with 2 turns/glucose CoA Citric acid cycle 3 NAD FADH2 3 NADH FAD 3 H ADP P ATP © 2014 Pearson Education, Inc. 2 CO2 i Figure 7.10b Acetyl CoA CoA CoA Citric acid cycle 2 CO2 3 NAD FADH2 3 NADH FAD 3 H ADP P ATP © 2014 Pearson Education, Inc. i Figure 7.UN09 Glycolysis ATP © 2014 Pearson Education, Inc. Pyruvate oxidation Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis ATP ATP Figure 7.5 H2 ½ O2 2H Controlled release of energy Free energy, G Free energy, G 2 H 2 e− Explosive release ATP ATP ATP 2 e− 2 © 2014 Pearson Education, Inc. ½ O2 H H2O (a) Uncontrolled reaction ½ O2 H2O (b) Cellular respiration The Pathway of Electron Transport The electron transport chain is in the inner membrane of the mitochondrion Most of the chain’s components are proteins, which exist in multiprotein complexes Some of these proteins are “cytochromes” and contain Fe atoms 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 In prokaryotes, this process takes place in the plasma membrane (this is important) © 2014 Pearson Education, Inc. Figure 7.14 Here’s a closer look Intermembrane space H H H Protein complex of electron carriers H Cyt c IV Q Glycolysis & Krebs cycle III I NADH II FADH2 FAD 2 H ½ O2 ATP synthase H2O NAD ADP P (carrying electrons from food) H 1 Electron transport chain Oxidative phosphorylation Matrix © 2014 Pearson Education, Inc. ATP i 2 Chemiosmosis 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. Figure 7.14b So then, where does the ATP get generated? • • • • • ATPase is an integral membrane protein More of a motor than an enzyme Allows H+ to pass through by chemiosmosis As this happens the H+ release free energy (ie. exergonic) which is used to do work – make ATP This gradient is called the proton-motive force due to its ability to do work © 2014 Pearson Education, Inc. H ATP synthase ADP P ATP i H 2 Chemiosmosis Video: ATP Synthase 3-D Side View Video: ATP Synthase 3-D Top View © 2014 Pearson Education, Inc. Figure 7.15 So, this is the forest, and the trees Electron shuttles span membrane CYTOSOL 2 NADH 6 NADH 2 NADH Glycolysis Glucose MITOCHONDRION 2 NADH or 2 FADH2 2 Pyruvate Pyruvate oxidation 2 Acetyl CoA 2 ATP Maximum per glucose: 2 FADH2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis 2 ATP about 26 or 28 ATP About 30 or 32 ATP Can you draw this process? Can you explain it? © 2014 Pearson Education, Inc. Tally of the ATP During cellular respiration, most energy flows in the following sequence: glucose NADH electron transport chain proton-motive force ATP The ETC produces ~26-28 ATP Glycolysis = 2 ATP net Krebs = 2 ATP (1/turn, 2 turns/glucose) Therefore the total generated = 36 (or 34 depending on who you ask) © 2014 Pearson Education, Inc. Concept 7.5: 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 fermentation or anaerobic respiration 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 from pyruvate, and the second step reduces acetaldehyde to ethanol Alcohol fermentation by yeast is used in brewing, winemaking, and baking Animation: Fermentation Overview © 2014 Pearson Education, Inc. Figure 7.16 2 ADP 2 P Glucose 2 ADP 2 P 2 ATP i Glycolysis Glucose 2 ATP i Glycolysis 2 Pyruvate 2 NAD 2 NADH 2 H 2 NAD 2 CO2 2 NADH 2 H 2 Pyruvate 2 Ethanol (a) Alcohol fermentation © 2014 Pearson Education, Inc. 2 Acetaldehyde 2 Lactate (b) Lactic acid fermentation Figure 7.16a 2 ADP 2 P Glucose 2 ATP i Glycolysis 2 Pyruvate 2 NAD 2 Ethanol (a) Alcohol fermentation © 2014 Pearson Education, Inc. 2 NADH 2 H 2 CO2 2 Acetaldehyde Figure 7.16b 2 ADP 2 P Glucose 2 ATP i Glycolysis 2 NAD 2 NADH 2 H 2 Pyruvate 2 Lactate (b) Lactic acid fermentation © 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 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 © 2014 Pearson Education, Inc. Obligate anaerobes carry out only 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 7.17 Glucose CYTOSOL Glycolysis Pyruvate No O2 present: Fermentation O2 present: Aerobic cellular respiration MITOCHONDRION Ethanol, lactate, or other products Acetyl CoA Citric acid cycle © 2014 Pearson Education, Inc. 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 7.6: 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 Glycolysis accepts a wide range of carbohydrates Proteins must be digested to amino acids and amino groups must be removed before amino acids can feed glycolysis or the citric acid cycle Fats are digested to glycerol and fatty acids 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 7.18-5 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 Some of these small molecules come directly from food; others can be produced during glycolysis or the citric acid cycle © 2014 Pearson Education, Inc. Figure 7.UN11 Inputs Outputs Glycolysis Glucose © 2014 Pearson Education, Inc. 2 Pyruvate 2 ATP 2 NADH Figure 7.UN12 Outputs Inputs 2 Pyruvate 2 Acetyl CoA 2 Oxaloacetate © 2014 Pearson Education, Inc. Citric acid cycle 2 ATP 6 CO2 2 FADH2 8 NADH 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.