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Chapter 6 How Cells Harvest Chemical Energy PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings How Is a Marathoner Different from a Sprinter? • Human muscles contain two different types of muscle fibers – That perform differently under different conditions Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • The different types of muscle fibers – Function either aerobically, with oxygen, or anaerobically, without oxygen • Cellular respiration – Is the process by which cells produce energy aerobically Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 1 INTRODUCTION TO CELLULAR RESPIRATION 6.1 Photosynthesis and cellular respiration provide energy for life • Cellular respiration makes ATP and consumes O2 – During the oxidation of glucose to CO2 and H2O Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • Photosynthesis uses solar energy – To produce glucose and O2 from CO2 and H2O Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts Glucose CO2 + + H2 O O2 Cellular respiration in mitochondria ATP (for cellular work) Heat energy Figure 6.1 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.2 Breathing supplies oxygen to our cells and removes carbon dioxide • Breathing provides for the exchange of O2 and CO2 – Between an organism and its environment O2 CO2 Breathing Lungs CO2 Bloodstream O2 Muscle cells carrying out Cellular Respiration Glucose + O2 Figure 6.2 CO2 + H2O + ATP Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 2 6.3 Cellular respiration banks energy in ATP molecules • Cellular respiration breaks down glucose molecules – And banks their energy in ATP C6H 12O6 Glucose + 6 O2 Oxygen gas 6 CO2 + Carbon dioxide 6 H2O + Water ATPs Energy Figure 6.3 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CONNECTION 6.4 The human body uses energy from ATP for all its activities • ATP powers almost all cellular and body activities Table 6.4 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen • Electrons lose potential energy – During their transfer from organic compounds to oxygen Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 3 • When glucose is converted to carbon dioxide – It loses hydrogen atoms, which are added to oxygen, producing water Loss of hydrogen atoms (oxidation) C6H 12O6 + 6 O2 6 CO2 + 6 H2O + Energy Glucose (ATP) Gain of hydrogen atoms (reduction) Figure 6.5A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • Dehydrogenase removes electrons (in hydrogen atoms) from fuel molecules (oxidation) – And transfers them to NAD+ (reduction) H O NAD+ Oxidation H + O + 2H Dehydrogenase Reduction 2H 2H+ + NADH + H+ (carries 2 electrons) 2e− Figure 6.5B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • NADH passes electrons – To an electron transport chain • As electrons “fall” from carrier to carrier and finally to O2 – Energy is released in small quantities NADH !ATP NAD+ + 2e− Controlled release of energy for synthesis of ATP H+ tra Ele ns c po t r o rt n ch ain 2e− 2 H+ Figure 6.5C 1 2 O2 H2O Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 4 STAGES OF CELLULAR RESPIRATION AND FERMENTATION • 6.6 Overview: Cellular respiration occurs in three main stages • Cellular respiration – Occurs in three main stages Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • Stage 1: Glycolysis – Occurs in the cytoplasm – Breaks down glucose into pyruvate, producing a small amount of ATP Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • Stage 2: The citric acid cycle – Takes place in the mitochondria – Completes the breakdown of glucose, producing a small amount of ATP – Supplies the third stage of cellular respiration with electrons Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 5 • Stage 3: Oxidative phosphorylation – Occurs in the mitochondria – Uses the energy released by “falling” electrons to pump H+ across a membrane – Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • An overview of cellular respiration NADH High-energy electrons carried by NADH NADH FADH2 and GLYCOLYSIS Glucose Pyruvate OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) CITRIC ACID CYCLE Mitochondrion Cytoplasm CO2 ATP ATP Substrate-level phosphorylation ATP CO2 Substrate-level phosphorylation Oxidative phosphorylation Figure 6.6 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • In glycolysis, ATP is used to prime a glucose molecule – Which is split into two molecules of pyruvate 2 NAD+ 2 NADH + 2 H+ Glucose 2 Pyruvate 2 ADP +2 P 2 ATP Figure 6.7A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6 • Glycolysis produces ATP by substrate-level phosphorylation – In which a phosphate group is transferred from an organic molecule to ADP Enzyme P Adenosine P P ATP ADP P Organic molecule (substrate) P Figure 6.7B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • In the first phase of glycolysis – ATP is used to energize a glucose molecule, which is then split in two Steps 1 – 3 A fuel molecule is energized, using ATP. PREPARATORY PHASE (energy investment) Glucose ATP Step 1 ADP P Glucose-6-phosphate P Fructose-6-phosphate P Fructose-1,6-diphosphate 2 ATP 3 ADP P Step 4 A six-carbon intermediate splits into two three-carbon intermediates. 4 Figure 6.7C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • In the second phase of glycolysis – ATP, NADH, and pyruvate are formed P Step 6 9 NADH. P Glyceraldehyde-3-phosphate (G3P) 5 A redox reaction generates NAD+ +H+ P ADP P 6 7 6 ATP P P 7 P 8 8 H2 O 7 P 3 -Phosphoglycerate 7 8 2-Phosphoglycerate 8 H2 O P P 9 ADP Phosphoenolpyruvate (PEP) 9 ADP 9 Figure 6.7C 6 P 1,3 -Diphosphoglycerate ADP ATP ATP ENERGY PAYOFF PHASE 5 P 6 NADH +H+ P P NADH Steps 6 – 9 ATP and pyruvate are produced. NAD+ 5 9 ATP Pyruvate Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 7 6.8 Pyruvate is chemically groomed for the citric acid cycle • Prior to the citric acid cycle – Enzymes process pyruvate, releasing CO2 and producing NADH and acetyl CoA + H+ NADH NAD+ 2 CoA Pyruvate Acetyl CoA (acetyl coenzyme A) 1 3 CO2 Coenzyme A Figure 6.8 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.9 The citric acid cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules • In the citric acid cycle – The two-carbon acetyl part of acetyl CoA is oxidized Acetyl CoA CoA CoA CITRIC ACID CYCLE 2 CO2 3 NAD+ FADH2 3 NADH FAD + 3 H+ ATP Figure 6.9A ADP + P Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • The two carbons are added to a four-carbon compound, forming citrate – Which is then degraded back to the starting compound Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 8 • For each turn of the cycle – Two CO2 molecules are released – The energy yield is one ATP, three NADH, and one FADH2 CoA Acetyl CoA CoA 2 carbons enter cycle Oxaloacetate 1 Citrate + H+ NADH NAD + 5 CO2 leaves cycle 2 CITRIC ACID CYCLE NAD + + Malate NADH + H ADP + P FADH2 4 ATP Alpha-ketoglutarate FAD 3 CO2 leaves cycle Succinate NADH + H+ NAD Step 1 Steps 2 and 3 Acetyl CoA stokes the furnace. NADH, ATP, and CO2 are generated during redox reactions. Figure 6.9B + Steps 4 and 5 Redox reactions generate FADH2 and NADH. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.10 Most ATP production occurs by oxidative phosphorylation • Electrons from NADH and FADH2 – Travel down the electron transport chain to oxygen, which picks up H+ to form water • Energy released by the redox reactions – Is used to pump H+ into the space between the mitochondrial membranes Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes – Driving the synthesis of ATP H+ . H+ Inner mitochondrial membrane FADH2 Electron flow NADH H+ H+ Electron carrier Intermembrane space Mitochondrial matrix H+ H+ H+ Protein complex H+ H+ ATP synthase FAD NAD+ H+ 1 O H+ 2 2 +2 H+ H+ H2 O Electron Transport Chain ADP + P H+ ATP Chemiosmosis OXIDATIVE PHOSPHORYLATION Figure 6.10 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 9 CONNECTION 6.11 Certain poisons interrupt critical events in cellular respiration • Various poisons – Block the movement of electrons – Block the flow of H+ through ATP synthase – Allow H+ to leak through the membrane Cyanide, carbon monoxide Rotenone + H + H + Oligomycin + H + H H + H + H + H + H ATP Synthase DNP FADH2 NADH NAD FAD +2 H+ 1 O2 2 + + H + H ADP + P H2 O + H Electron Transport Chain Figure 6.11 ATP Chemiosmosis Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.12 Review: Each molecule of glucose yields many molecules of ATP • Oxidative phosphorylation, using electron transport and chemiosmosis – Produces up to 38 ATP molecules for each glucose molecule that enters cellular respiration Electron shuttle across membrane Cytoplasm Mitochondrion 2 NADH 2 NADH (or 2 FADH2 ) 2 NADH GLYCOLYSIS 2 Glucose Pyruvate 2 Acetyl CoA + 2 ATP 6 NADH CITRIC ACID CYCLE + 2 ATP by substrate-level phosphorylation by substrate-level phosphorylation Maximum per glucose: 2 FADH2 OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) + about 34 ATP by oxidative phosphorylation About 38 ATP Figure 6.12 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.13 Fermentation is an anaerobic alternative to cellular respiration • Under anaerobic conditions, many kinds of cells – Can use glycolysis alone to produce small amounts of ATP Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 10 • In lactic acid fermentation – NADH is oxidized to NAD+ as pyruvate is reduced to lactate 2 2 NAD+ 2 NADH NADH 2 NAD+ GLYCOLYSIS 2 ADP + 2 P 2 ATP 2 Pyruvate Glucose 2 Lactate Figure 6.13A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • In alcohol fermentation – NADH is oxidized to NAD+ while converting pyruvate to CO2 and ethanol 2 NAD+ 2 NADH 2 NADH NAD+ 2 GLYCOLYSIS 2 ADP +2 P Glucose 2 2 ATP CO2 released 2 !Ethanol 2 Pyruvate Figure 6.13B Figure 6.13C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS • 6.14 Cells use many kinds of organic molecules as fuel for cellular respiration Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 11 • Carbohydrates, fats, and proteins can all fuel cellular respiration – When they are converted to molecules that enter glycolysis or the citric acid cycle Food, such as peanuts Carbohydrates Fats Sugars Glycerol Proteins Fatty acids Amino acids Amino groups Glucose G3P Pyruvate GLYCOLYSIS OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) CITRIC ACID CYCLE Acetyl CoA ATP Figure 6.14 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.15 Food molecules provide raw materials for biosynthesis • Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials • This process of biosynthesis ATP needed to drive biosynthesis ATP – Consumes ATP CITRIC ACID CYCLE GLUCOSE SYNTHESIS Acetyl CoA Pyruvate G3P Glucose Amino groups Amino acids Proteins Fatty acids Glycerol Fats Sugars Carbohydrates Cells, tissues, organisms Figure 6.15 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.16 The fuel for respiration ultimately comes from photosynthesis • All organisms – Can harvest energy from organic molecules • Plants, but not animals – Can also make these molecules from inorganic sources by the process of photosynthesis Figure 6.16 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 12