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Chapter 9 Cellular Respiration: Harvesting Chemical Energy PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Life Is Work • Living cells – Require transfusions of energy from outside sources to perform their many tasks Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The giant panda – Obtains energy for its cells by eating plants Figure 9.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy – Flows into an ecosystem as sunlight and leaves as heat Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic CO2 + H2O + O2 Cellular molecules respiration in mitochondria ATP powers most cellular work Figure 9.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Heat energy Catabolic Pathways and Production of ATP • The breakdown of organic molecules is exergonic (releasing energy) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings One catabolic process, fermentation – Is a partial degradation of sugars that occurs without oxygen – Aerobic- with oxygen – Anaerobic- without oxygen Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular respiration – Is the most common and efficient breakdown of energy from food – Consumes (takes) oxygen and organic molecules such as glucose – Yields (produces) ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings To keep working – Cells must regenerate ATP – ATP- The energy currency for cells to do work (grow, divide, function) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Redox Reactions: Oxidation and Reduction • Catabolic pathways yield energy – Due to the transfer of electrons Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Organic Fuel Molecules During Cellular Respiration • During cellular respiration: C6H12O6 + 6O2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 6CO2 + 6H2O + Energy The Stages of Cellular Respiration: A Preview • Respiration is a cumulative function of three metabolic stages – Glycolysis – Krebs cycle (also known as The citric acid cycle) – Electron Transport Chain Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stages and Locations of Cellular Respiration – Glycolysis (doesn’t require oxygen) happens in the cytoplasm of cell – Krebs cycle/ Citric Acid Cycle (Needs oxygen) happens in the fluid of mitochondria – Electron Transport Chain/ Oxidative phosphorylation (needs oxygen) happens in the mitochondria membrane Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis -> Krebs Cycle -> Electron Transport Chain • STEP 1: Glycolysis – Breaks down glucose into two molecules of pyruvate – Glucose -- pyruvate • STEP 2: Krebs Cycle/ The citric acid cycle – Completes the breakdown of glucose Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis -> Krebs Cycle -> Electron Transport Chain • STEP 3: Electron Transport Chain – Is driven by the electron transport chain – Generates ATP (energy currency) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of cellular respiration Electrons carried via NADH and FADH2 Electrons carried via NADH Citric acid cycle Glycolsis Pyruvate Glucose Cytosol Mitochondrion ATP re 9.6 Oxidative phosphorylation: electron transport and chemiosmosis Substrate-level phosphorylation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP Substrate-level phosphorylation ATP Oxidative phosphorylation Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate Glucose Goes in • Glycolysis – Means “splitting of sugar” – Breaks down glucose into pyruvate – Occurs in the cytoplasm of the cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvate ATP Come out Krebs Cycle/ Citric Acid Cycle • The citric acid cycle completes the energyyielding oxidation of organic molecules • The citric acid cycle – Takes place in the matrix of the mitochondrion Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of the citric acid cycle/ Krebs Cycle Pyruvate goes in Pyruvate (from glycolysis, 2 molecules per glucose) Glycolysis Citric acid cycle ATP ATP Oxidative phosphorylatio n ATP CO2 CoA NADH + 3 H+ Acetyle CoA CoA CoA FADH2 ATP NADH CO2 Citric acid cycle 2 CO2 3 NAD+ FADH2 FAD 3 NADH + 3 H+ ADP + P i Come out ATP Figure 9.11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electron Transport Chain ATP synthesis • Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis • NADH and FADH2 (Products of Krebs Cycle) – Donate electrons in the electron transport chain which powers ATP synthesis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At the end of the Electron Transport Chain – Electrons are passed to oxygen, forming water NADH 50 Free energy (G) relative to O2 (kcl/mol) FADH2 40 I FMN Multiprotein complexes FAD Fe•S Fe•S II O III Cyt b 30 Fe•S Cyt c1 IV Cyt c Cyt a Cyt a3 20 10 0 Figure 9.13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 H + + 12 O2 H2 O There are three main processes in this metabolism Electron shuttles span membrane CYTOSOL MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH Glycolysis Glucose 2 Pyruvate 6 NADH Citric acid cycle 2 Acetyl CoA + 2 ATP by substrate-level phosphorylation Maximum per glucose: + 2 ATP 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP by substrate-level by oxidative phosphorylation, depending on which shuttle transports electrons phosphorylation from NADH in cytosol About 36 or 38 ATP Figure 9.16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings There are three main processes in this metabolism SIMPLIFIED! Electron shuttles span membrane CYTOSOL MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH Glycolysis Glucose 2 Pyruvate 6 NADH Citric acid cycle 2 Acetyl CoA + 2 ATP + 2 ATP Maximum per glucose: About 36 or 38 ATP Figure 9.16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP About 40% of the energy in a glucose molecule – Is transferred to ATP during cellular respiration, making between 36-38 ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.5: Fermentation- some cells can produce ATP without the use of oxygen – (anaerobic) • Cellular respiration – Relies on oxygen to produce ATP • Fermentation – Cells can still produce ATP in the absence of Oxygen Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis – Can produce ATP with or without oxygen, in aerobic or anaerobic conditions – Couples with fermentation to produce ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Fermentation • Alcohol Fermentation- Happens with yeast • Lactic Acid Fermentation- happens in our bodies after exercise. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In alcohol fermentation – Pyruvate is converted to ethanol in two steps, one of which releases CO2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings During lactic acid fermentation – Pyruvate is reduced directly to NADH to form lactate as a waste product Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Alcohol Fermentation -> ethanol Lactic acid Fermentation -> lactic acid 2 ADP + 2 P1 2 ATP O– C O Glucose Glycolysis C O CH3 2 Pyruvate 2 NADH 2 NAD+ H 2 CO2 H H C OH C O CH3 CH3 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation 2 ADP + 2 Glucose P1 2 ATP Glycolysis O– C O C O O 2 NAD+ 2 NADH C O H C OH CH3 2 Lactate Figure 9.17 (b) Lactic acid fermentation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CH3 Fermentation and Cellular Respiration Compared • Both fermentation and cellular respiration – Use glycolysis to oxidize glucose and other organic fuels to pyruvate Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation vs. Cellular Respiration • Cellular respiration – Produces more ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvate is a key juncture in catabolism • (Catabolism is the metabolic breakdown of complex molecules into simpler ones, often resulting in a release of Glucose energy.) CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Figure 9.18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acetyl CoA Citric acid cycle The Evolutionary Significance of Glycolysis • Glycolysis – Occurs in nearly all organisms – Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Biosynthesis (Anabolic Pathways) • The body – Uses small molecules to build other substances • These small molecules – May come directly from food or through glycolysis or the citric acid cycle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings