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INTRODUCTION TO CELLULAR RESPIRATION • Need Energy for work • ATP = usable energy • Cells make ATP by breaking down sugar – Aerobic cell respiration – uses oxygen – Anaerobic cell respiration – no oxygen – Facultative Anaerobe – can use oxygen or not Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 Cellular respiration banks energy in ATP molecules • Breakdown sugar to get electrons to use energy to make ATP Glucose Oxygen gas Figure 6.2A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Carbon dioxide Water Energy BASIC MECHANISMS OF ENERGY RELEASE AND STORAGE Cells tap energy from electrons transferred from organic fuels to oxygen • LEO / GER • Oxidation: Lose Electrons Loss of hydrogen atoms • Reduction: Gain Electrons Energy Glucose Gain of hydrogen atoms Figure 6.4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Electron Transfer • Sugar has electrons • Break down sugar to get electrons (sugar gets oxidized) • NAD+ gains electrons (becomes oxidized) NADH [also FAD + electrons FADH2] • Eventually NADH gives electrons to oxygen, and in process make ATP and water Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings STAGES OF CELLULAR RESPIRATION AND FERMENTATION Overview: Respiration occurs in three main stages • Cellular respiration oxidizes sugar and produces ATP in three main stages – 1. Glycolysis ( cytoplasm ) – 2. Pyruvate Dehydrogenase Complex PDC (matrix) – 3. Krebs Cycle (matrix) – 4. Electron Transport Chain (cristae) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS Glucose Pyruvic acid Cytoplasmic fluid Figure 6.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion 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 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 The Krebs cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules Acetyl CoA • The Krebs cycle- get more electrons from sugar molecule 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. Chemiosmosis powers most ATP production • NADH and FADH2 – give electrons to enzymes in electron transport chain that get passed to oxygen • Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes • 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 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 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 by substrate-level phosphorylation 2 Acetyl CoA used for shuttling electrons from NADH made in glycolysis KREBS CYCLE by substrate-level phosphorylation KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS by chemiosmotic phosphorylation Maximum per glucose: Figure 6.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Event Location Substrates Products Need Oxygen Glycolysis Cytoplasm Glucose, 2 ATP 2 Pyruvate, 2 ATP, 2 NADH No PDC Matrix Pyruvate Acetyl CoA, 2 NADH, CO2 No(but need products from ETC) Krebs Cycle Matrix Acetyl CoA, Oxaloacetic Acid Electron Transport Chain Inner membrane – cristae 10 NADH 2 FADH2 Oxygen Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings (must go 2x) Oxaloacetic Acid, 3 NADH, 1 ATP, 1 FADH2 NAD, FAD, ATP, water No(but need products from ETC) Yes 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