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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? • Muscles in human legs contain two different types of muscle fibers – Marathoners have more slow-twitch fibers, which perform better in endurance exercises – Sprinters have more fast-twitch fibers, which perform best in short bursts of intense activity – Chickens can relate Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • The different types of muscle fibers use different processes for making ATP – Slow-twitch fibers undergo aerobic (in the presence of O2) respiration – Fast-twitch fibers undergo anaerobic (in the absence of O2) respiration • Cellular respiration is the process by which cells produce energy aerobically Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings INTRODUCTION TO CELLULAR RESPIRATION 6.1 Photosynthesis and cellular respiration provide energy for life • All living organisms require energy to maintain homeostasis, to move, and to reproduce • Photosynthesis converts energy from the sun to glucose and O2 • Cellular respiration breaks down glucose and releases energy in ATP • Energy flows through an ecosystem; chemicals are recycled Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-1 Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts CO2 Glucose H2O O2 Cellular respiration in mitochondria ATP (for cellular work) Heat energy D. Energy and Exercise (refer to activity sheet) E. Comparing Photosynthesis and Cellular Respiration Photosynthesis Function Cellular Respiration Energy Capture Energy Release Chloroplasts Mitochondria H2O and CO2 C6H12O6 and O2 C6H12O6 and O2 H2O and CO2 Location Reactants Products Equation 6H2O + 6CO2 → C6H12O6 + 6O2 C6H12O6 + 6O2 → 6H2O + 6CO2 6.2 Breathing supplies oxygen to our cells and removes carbon dioxide • Breathing and cellular respiration are closely related – Breathing brings O2 into the body from the environment – O2 is distributed to cells in the bloodstream – In cellular respiration, mitochondria use O2 to harvest energy and generate ATP – Breathing disposes of the CO2 produced as a waste product of cellular respiration Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-2 O2 Breathing CO2 Lungs CO2 Bloodstream O2 Muscle cells carrying out Cellular Respiration Glucose O2 CO2 H2O ATP 6.3 Cellular respiration banks energy in ATP molecules • The reactants O2 and glucose regroup to form the products CO2 and H2O • Energy from glucose is released and stored in ATP Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-3 Glucose Oxygen gas Carbon dioxide Water Energy CONNECTION 6.4 The human body uses energy from ATP for all its activities • The body needs a continual supply of energy to maintain basic functioning • In addition, ATP supplies energy (kilocalories) for voluntary activities • An average adult human needs about 2,200 kcal of energy each day Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen • The energy available to a cell is contained in the arrangement of electrons in chemical bonds • Electrons lose potential energy when they “fall” from organic compounds to oxygen during cellular respiration • Each step of the “fall” involves paired oxidation–reduction (redox) reactions – Oxidation: loss of electrons (in atoms) – Reduction: addition of electrons Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • 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 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • The redox reactions of cellular respiration – Glucose loses electrons (in H atoms) and becomes oxidized – O2 gains electrons (in H atoms) and becomes reduced – Along the way, the electrons lose potential energy, and energy is released Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • Glucose gives up energy as it is oxidized Loss of hydrogen atoms Energy Glucose Gain of hydrogen atoms Figure 6.4 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • The redox reactions that break down glucose involve an enzyme and a coenzyme – The enzyme dehydrogenase removes electrons (in H atoms) from fuel molecules (oxidation) – The electrons are transferred to the coenzyme NAD+, which is converted to NADH (reduction) Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Oxidation Dehydrogenase Reduction NAD NADH 2H 2H 2 e (carries 2 electrons) H – 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 • The energy released is used by the cell to make ATP Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-5c NADH ATP NAD 2e Controlled release of energy for synthesis H of ATP 2e 2 1 2 H H2O O2 Two mechanisms generate ATP http://www.sp.uconn.edu/~terry/Common/respiration.html • 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 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings High H+ concentration ATP synthase uses gradient energy to make ATP Membrane Electron transport chain ATP synthase Energy from Low H+ concentration Figure 6.7A • 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 © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Overview of Glucose Breakdown • The overall equation for the complete breakdown of glucose is: C6H12O6 + 6O2 6CO2 + 6H2O + ATP • The main stages of glucose metabolism are: • Glycolysis • Cellular respiration Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Copyright © 2005 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 © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion Flowchart Section 9-2 Cellular Respiration Glucose (C6H1206) + Oxygen (02) Glycolysis Krebs Cycle Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Electron Transport Chain Carbon Dioxide (CO2) + Water (H2O) STAGES OF CELLULAR RESPIRATION AND FERMENTATION 6.6 Overview: Cellular respiration occurs in three main stages Stage 1: Glycolysis • Occurs in the cytoplasm • Breaks down glucose into pyruvate, producing a small amount of ATP Glucose Pyruvic acid • Stage 2: The citric acid cycle Acetyl CoA KREBS CYCLE KREBS CYCLE 2 CO2 – Takes place in the mitochondria – Completes the breakdown of glucose, producing CO2 and a small amount of ATP – Supplies the third stage of cellular respiration with electrons Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • Stage 3: Oxidative phosphorylation – Occurs in the mitochondria – Uses the energy released by electrons “falling” down the electron transport chain 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 LE 6-6 NADH High-energy electrons carried by NADH FADH2 NADH and GLYCOLYSIS Glucose CITRIC ACID CYCLE Pyruvate OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Cytoplasm Mitochondrion CO2 CO2 ATP Substrate-level phosphorylation ATP ATP Substrate-level phosphorylation Oxidative phosphorylation 6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • Glycolysis splits sugar molecules in the cytoplasm – Starts with a single 6-carbon molecule of glucose – Ends with two 3-carbon molecules of pyruvate – Produces two molecules of ATP in the process Animation: Glycolysis Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-7a 2 NAD 2 NADH 2 Glucose H 2 Pyruvate 2 ADP 2 P 2 ATP • Glycolysis produces ATP by substrate-level phosphorylation – An enzyme transfers a phosphate group from an organic molecule to ADP – A small amount of ATP is produced Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-7b Enzyme P P P Adenosine ADP ATP P Organic molecule (substrate) P • Details of glycolysis – A fuel molecule is energized, using ATP. Glucose 1Steps 3 Step PREPARATORY PHASE (energy investment) 1 Glucose-6-phosphate 2 Fructose-6-phosphate 3 Fructose-1,6-diphosphate 4 Step A six-carbon intermediate splits into two three-carbon intermediates. 4 Glyceraldehyde-3-phosphate (G3P) 5 5 Step A redox reaction generates NADH. 6 Steps6 –9 ATP and pyruvic acid are produced. ENERGY PAYOFF PHASE 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 NAD NADH H CoA Pyruvate Acetyl CoA (acetyl coenzyme A) CO2 Coenzyme A 6.11 The citric acid cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules • For each turn of the citric acid cycle – Two CO2 molecules are released – The energy yield is one ATP, three NADH, and one FADH2 Animation: Citric Acid Cycle Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-9a Acetyl CoA CoA CoA 2 CO2 CITRIC ACID CYCLE 3 FADH2 3 FAD NAD NADH 3 H ATP ADP P LE 6-9b CoA Acetyl CoA CoA 2 carbons enter cycle Oxaloacetate Citrate NADH H CO2 NAD leaves cycle NAD CITRIC ACID CYCLE Malate NADH ADP FADH2 P ATP Alpha-ketoglutarate FAD CO2 Succinate NADH H NAD leaves cycle H • Details of the citric acid cycle – The 2-carbon acetyl part of acetyl CoA is oxidized – The two carbons are added to a 4-compound, forming citrate – Through a series of redox reactions, two carbons are removed from citrate as CO2 and the 4-carbon compound is regenerated – The energy-rich molecules ATP, NADH, and FADH2 are produced Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings ETC/chemiosmosis Oxidative phosphorylation Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Chemiosmosis • Flow of hydrogen ions provides energy to link 32-34 molecules of ADP with phosphate, forming 32-34 ATP • ATP then diffuses out of mitochondrion and used for energy-requiring activities in the cell Link: ETC and chemiosmosis Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-10 H H H Protein complex Intermembrane space H H Electron carrier H H H H ATP synthase Inner mitochondrial membrane FADH2 Electron flow NADH Mitochondrial matrix FAD NAD H 1 2 O2 2 H H H H2O Electron Transport Chain OXIDATIVE PHOSPHORYLATION ADP P ATP H Chemiosmosis CONNECTION 6.11 Certain poisons interrupt critical events in cellular respiration • Rotenone, cyanide, and carbon monoxide block parts of the electron transport chain • Oligomycin blocks the passage of H+ through ATP synthase • Uncouplers such as DNP destroy the H+ gradient by making the membrane leaky to H+ Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-11 Rotenone Cyanide, carbon monoxide H+ H+ H+ Oligomycin H+ H+ H+ H+ H+ H+ ATP synthase DNP FAD FADH2 NAD NADH 1 2 + O2 + 2 H+ H+ H+ H2O ADP + P ATP H+ Electron Transport Chain Chemiosmosis 6.12 Review: Each molecule of glucose yields many molecules of ATP • Glycolysis and the citric acid cycle together yield four ATP per glucose molecule • Oxidative phosphorylation, using electron transport and chemiosmosis, yields 34 ATP per glucose • These numbers are maximums – Some cells may lose a few ATP to NAD+ or FAD shuttles Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-12 LINK:CELLULAR RESPIRATION VIDEO-CALIFORNICATION Electron shuttle across membrane Cytoplasm 2 NADH Mitochondrion 2 NADH (or 2 FADH2) 2 NADH 6 Glucose 2 Acetyl CoA 2 ATP by substrate-level phosphorylation Maximum per glucose: 2 FADH2 CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) 2 ATP about 34 ATP by substrate-level phosphorylation by oxidative phosphorylation GLYCOLYSIS 2 Pyruvate NADH About 38 ATP C. The Totals Per Glucose molecule 3 ATP ***note: each NADH produces __ 2 ATP each FADH2 produces __ Click on ATP synthesis and play the first one only http://www.wiley.com/legacy/college/boyer/0470003790/animations/electron_transport/electron_transport.htm LOCATION ATP NADH FADH2 BYPRODUCTS cytoplasm 2 2 0 ------ KREBS CYCLE: Pyruvate oxidation → matrix 0 2 0 Carbon dioxide Energy Extraction → matrix 2 6 2 Carbon dioxide Inner Membrane (Cristae) 34 0 0 water GLYCOLYSIS ELECTRON TRANSPORT CHAIN TOTALS (net) 36 2 -2 ATP (transport of pyruvic acid into mitochondria) 6.13 Fermentation is an anaerobic alternative to cellular respiration • Fermentation – Generates two ATP molecules from glycolysis in the absence of oxygen – Recycles NADH to NAD+ anaerobically • Muscle cells use lactic acid fermentation – NADH is oxidized to NAD+ as pyruvate is reduced to lactate Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-13a 2 NAD NADH 2 2 NADH 2 NAD GLYCOLYSIS 2 ADP 2 P 2 ATP 2 Pyruvate Glucose 2 Lactate • Alcohol fermentation occurs in brewing, wine making, and baking – NADH is oxidized to NAD+ while converting pyruvate to CO2 and ethanol Animation: Fermentation Overview Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-13b 2 NAD NADH 2 2 NADH 2 NAD GLYCOLYSIS 2 ADP Glucose 2 2 P 2 2 ATP 2 Pyruvate CO2 released 2 Ethanol Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • Strict anaerobes – Require anaerobic conditions to generate ATP by fermentation – Are poisoned by oxygen • Facultative anaerobes – Can make ATP by fermentation or oxidative phosphorylation depending on whether O2 is available Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings COMPARISON OF FERMENTATION TO CELLULAR REPIRATION Lactic Acid glucose Alcoholic glucose Cellular respiration glucose glycolysis (pyruvic acid) glycolysis (pyruvic acid) carbon dioxide carbon dioxide lactic acid alcohol water 2 ATP 2 ATP 38 ATP glycolysis (pyruvic acid) 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 Cells use three main kinds of food molecules to make ATP • Carbohydrates – Hydrolyzed by enzymes to glucose, which enters glycolysis • Proteins – Digested to constituent amino acids, which are transformed into various compounds – Become intermediates in glycolysis or the citric acid cycle Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings • Fats – Digested to glycerol and free fatty acids • Glycerol becomes an intermediate in glycolysis • Fatty acids are broken into 2-carbon fragments that enter the citric acid cycle as acetyl CoA Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-14 Food, such as peanuts Fats Carbohydrates Proteins Glycerol Fatty acids Sugars Amino acids Amino groups Glucose G3P Pyruvate Acetyl CoA GLYCOLYSIS ATP CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) 6.15 Food molecules provide raw materials for biosynthesis • Some raw materials from food can be incorporated directly into an organism’s molecules • Cells can also make molecules not found in food – Intermediate compounds of glycolysis and the citric acid cycle act as raw materials – Biosynthetic pathways consume ATP rather than generate it – Biosynthesis is not always the direct reverse of breakdown pathways Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LE 6-15 ATP needed to drive biosynthesis ATP CITRIC ACID CYCLE GLUCOSE SYNTHESIS Acetyl CoA Pyruvate G3P Glucose Amino groups Amino acids Proteins Fatty acids Glycerol Fats Cells, tissues, organisms Sugars Carbohydrates 6.16 The fuel for respiration ultimately comes from photosynthesis • All organisms can harvest energy from organic molecules • Plants can also make molecules from inorganic sources by photosynthesis Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings