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BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 6 How Cells Harvest Chemical Energy From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings How is a Marathoner Different from a Sprinter? • Long-distance runners have many slow fibers in their muscles – Slow fibers break down glucose for ATP production aerobically (using oxygen) – These muscle cells can sustain repeated, long contractions Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Sprinters have more fast muscle fibers – Fast fibers make ATP without oxygen— anaerobically – They can contract quickly and supply energy for short bursts of intense activity Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The dark meat of a cooked turkey is an example of slow fiber muscle – Leg muscles support sustained activity • The white meat consists of fast fibers – Wing muscles allow for quick bursts of flight Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Without Oxygen (Anaerobic) Fermentation occurs when cells do not have oxygen. The electron transport chain is stopped. Glycolysis is the only ATP producing mechanism. Lactic Acid and Alcoholic fermentation. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings INTRODUCTION TO CELLULAR RESPIRATION • Nearly all the cells in our body break down sugars for ATP production • Most cells of most organisms harvest energy aerobically, like slow muscle fibers – The aerobic harvesting of energy from sugar is called cellular respiration – Cellular respiration yields CO2, H2O, and a large amount of ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 6.1 Breathing supplies oxygen to our cells and removes carbon dioxide • Breathing and cellular respiration are closely related O2 BREATHING CO2 Lungs CO2 Bloodstream O2 Muscle cells carrying out CELLULAR RESPIRATION Sugar + O2 ATP + CO2 + H2O Figure 6.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 6.2 Cellular respiration banks energy in ATP molecules • Cellular respiration breaks down glucose molecules and banks their energy in ATP – The process uses O2 and releases CO2 and H2O Glucose Oxygen gas Figure 6.2A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Carbon dioxide Water Energy • The efficiency of cellular respiration (and comparison with an auto engine) Energy released from glucose (as heat and light) Energy released from glucose banked in ATP Gasoline energy converted to movement About 40% 25% 100% Burning glucose in an experiment “Burning” glucose in cellular respiration Figure 6.2B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Burning gasoline in an auto engine 6.3 Connection: The human body uses energy from ATP for all its activities • ATP powers almost all cell and body activities Table 6.3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings BASIC MECHANISMS OF ENERGY RELEASE AND STORAGE 6.4 Cells tap energy from electrons transferred from organic fuels to oxygen • Glucose gives up energy as it is oxidized Loss of hydrogen atoms Energy Glucose Gain of hydrogen atoms Figure 6.4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 6.5 Hydrogen carriers such as NAD+ shuttle electrons in redox reactions • Enzymes remove electrons from glucose molecules and transfer them to a coenzyme OXIDATION Dehydrogenase and NAD+ REDUCTION Figure 6.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 6.6 Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen • NADH delivers electrons to a series of electron carriers in an electron transport chain – As electrons move from carrier to carrier, their energy is released in small quantities Electron flow Figure 6.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • In an explosion, 02 is reduced in one step Energy released as heat and light Figure 6.6B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 6.7 Two mechanisms generate ATP • Cells use the energy released by “falling” electrons to pump H+ ions across a membrane – The energy of the gradient is harnessed to make ATP by the process of chemiosmosis High H+ concentration Membrane Electron transport chain ATP synthase Energy from Low H+ concentration Figure 6.7A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings ATP synthase uses gradient energy to make ATP Chemiosmosis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis H2O Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • ATP can also be made by transferring phosphate groups from organic molecules to ADP – This process is called substrate-level phosphorylation Enzyme Adenosine Organic molecule (substrate) Adenosine New organic molecule (product) Figure 6.7B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings STAGES OF CELLULAR RESPIRATION AND FERMENTATION 6.8 Overview: Respiration occurs in three main stages • Cellular respiration oxidizes sugar and produces ATP in three main stages – Glycolysis occurs in the cytoplasm – The Krebs cycle and the electron transport chain occur in the mitochondria Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS Glucose KREBS CYCLE Pyruvic acid Cytoplasmic fluid 2 ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion 2 Figure 6.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 32 6.9 Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid Glucose Figure 6.9A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvic acid • Details of glycolysis Steps 1 – 3 A fuel molecule is energized, using ATP. Glucose Step PREPARATORY PHASE (energy investment) 1 Glucose-6-phosphate 2 Fructose-6-phosphate 3 Fructose-1,6-diphosphate Step 4 A six-carbon intermediate splits into two three-carbon intermediates. 4 Glyceraldehyde-3-phosphate (G3P) ENERGY PAYOFF PHASE 5 Step 5 A redox reaction generates NADH. 6 Steps 6 – 9 ATP and pyruvic acid are produced. 1,3-Diphosphoglyceric acid (2 molecules) 7 3-Phosphoglyceric acid (2 molecules) 8 2-Phosphoglyceric acid (2 molecules) 2-Phosphoglyceric acid (2 molecules) 9 Figure 6.9B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvic acid (2 molecules per glucose molecule) 6.10 Pyruvic acid is chemically groomed for the Krebs cycle • Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle Pyruvic acid Acetyl CoA (acetyl coenzyme A) CO2 Figure 6.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 6.11 The Krebs cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules Acetyl CoA • The Krebs cycle is a series of reactions in which enzymes strip away electrons and H+ from each acetyl group KREBS CYCLE Figure 6.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 CO2 2 carbons enter cycle Oxaloacetic acid 1 Citric acid CO2 leaves cycle 5 KREBS CYCLE 2 Malic acid 4 Alpha-ketoglutaric acid 3 CO2 leaves cycle Succinic acid Step 1 Acetyl CoA stokes the furnace Steps 2 and 3 NADH, ATP, and CO2 are generated during redox reactions. Figure 6.11B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Steps 4 and 5 Redox reactions generate FADH2 and NADH. 6.12 Chemiosmosis powers most ATP production • The electrons from NADH and FADH2 travel down the electron transport chain to oxygen • Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes • In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Chemiosmosis in the mitochondrion Protein complex Intermembrane space Electron carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN Figure 6.12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings ATP SYNTHASE 6.13 Connection: Certain poisons interrupt critical events in cellular respiration Rotenone Cyanide, carbon monoxide ELECTRON TRANSPORT CHAIN Figure 6.13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Oligomycin ATP SYNTHASE 6.14 Review: Each molecule of glucose yields many molecules of ATP • For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules Cytoplasmic fluid Mitochondrion Electron shuttle across membranes GLYCOLYSIS 2 Glucose Pyruvic acid 2 Acetyl CoA KREBS CYCLE KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS 32 ATP by substrate-level phosphorylation used for shuttling electrons from NADH made in glycolysis Maximum per glucose: by substrate-level phosphorylation 36 ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings by chemiosmotic phosphorylation Figure 6.14 6.15 Fermentation is an anaerobic alternative to aerobic respiration • Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP – But a cell must have a way of replenishing NAD+ Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • In alcoholic fermentation, pyruvic acid is converted to CO2 and ethanol – This recycles NAD+ to keep glycolysis working released GLYCOLYSIS Glucose 2 Pyruvic acid Figure 6.15A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 Ethanol Figure 6.15C • In lactic acid fermentation, pyruvic acid is converted to lactic acid – As in alcoholic fermentation, NAD+ is recycled • Lactic acid fermentation is used to make cheese and yogurt GLYCOLYSIS Glucose 2 Pyruvic acid Figure 6.15B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 Lactic acid Cellular Respiration • Cellular Respiration – releases energy from the bonds of organic molecules • C6H12O6 + O2 H2O + CO2 + Energy 3 Stages Glycolysis Kreb’s (Citric Acid Cycle) Electron Transport Chain Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis • Glycolysis – sugar breakdown • Glucose is split into 2 pyruvate molecules • 2 net ATP are produced (-2 +4 = 2) • 2 NADH are also produced Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Kreb’s Cycle • Oxidation of Acetyl CoA • Each glucose (2 pyruvates) yields 2 ATP 6 NADH 2 FADH2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Electron Transport Chain and Chemiosmosis • The electron transport chain is the part of respiration that produces the most ATP and requires oxygen. • The electrons that are carried in NADH and FADH2 molecules are used to produce ATP through Chemiosmosis. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Net Yield of Cellular Respiration Glycolysis – 2 ATP Krebs Cycle – 2 ATP Electron Transport – 32 ATP Each glucose yields 36 ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis (fermentation); ETC • http://www.youtube.com/watch?v=uTILYYNxxE • http://www.youtube.com/watch?v=kN5MtqAB _Yc&feature=related Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings