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Cellular Respiration and Fermentation

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Cellular Respiration and Fermentation Chapter 9 Cellular Respiration and Fermentation Dr. Wendy Sera Houston Community College Biology 1406 © 2014 Pearson Education, Inc. Chapter 9 Concepts 1. Catabolic pathways yield energy by oxidizing organic fuels. 2. Glycolysis harvests chemical energy by oxidizing glucose to pyruvate. 3. After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules. 4. During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis. © 2014 Pearson Education, Inc. 5. Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen. 6. Glycolysis and the citric acid cycle connect to many other metabolic pathways. © 2014 Pearson Education, Inc. 1 Life Is Work . Living cells require energy from outside sources . Some animals, such as the giraffe, obtain energy by eating plants (herbivores/primary consumers), and some animals feed on other organisms that eat plants (carnivories/secondary consumers) Figure 9.1—How do these leaves power the work of life for this giraffe? © 2014 Pearson Education, Inc. Energy Flow and Nutrient Cycling in Ecosystems . Energy flows into an ecosystem as sunlight and leaves as heat . Photosynthesis generates O2 and organic molecules (e.g., glucose), which are used in cellular respiration . Cells use chemical energy stored in organic molecules to regenerate ATP, which powers cellular work © 2014 Pearson Education, Inc. Figure 9.2— Light Energy flow energy and chemical ECOSYSTEM recycling in ecosystems Photosynthesis in chloroplasts Organic CO + H O O 2 2 molecules+ 2 Cellular respiration in mitochondria ATP powers ATP most cellular work Heat energy © 2014 Pearson Education, Inc. 2 BioFlix: The Carbon Cycle © 2014 Pearson Education, Inc. Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels . Catabolic pathways release stored energy by breaking down complex molecules . Electron transfers (i.e., redox reactions) play a major role in these pathways . These processes are central to cellular respiration © 2014 Pearson Education, Inc. Catabolic Pathways and Production of ATP . The breakdown of organic molecules is exergonic . Fermentation is a partial degradation of sugars that occurs without O2 and yields very little ATP . Aerobic respiration consumes organic molecules and O2 and yields ATP . Anaerobic respiration is similar to aerobic respiration, but consumes compounds other than O2 and yields same amount of ATP as aerobic respiration © 2014 Pearson Education, Inc. 3 . Cellular respiration includes both aerobic and anaerobic respiration, but is often used to refer to aerobic respiration . Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat) © 2014 Pearson Education, Inc. Redox Reactions: Oxidation and Reduction . The transfer of electrons during chemical reactions releases energy stored in organic molecules . This released energy is ultimately used to synthesize ATP © 2014 Pearson Education, Inc. The Principle of Redox . Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions . In oxidation, a substance loses electrons, or is oxidized . In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced) © 2014 Pearson Education, Inc. 4 becomes oxidized (loses electron) becomes reduced (gains electron) © 2014 Pearson Education, Inc. becomes oxidized becomes reduced © 2014 Pearson Education, Inc. The electron donor is called the reducing agent . The electron receptor is called the oxidizing agent . Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds . An example is the reaction between methane and O2 (or the burning of any fuel!) © 2014 Pearson Education, Inc. 5 Figure 9.3—Methane combustion as an energy-yielding redox reaction Reactants Products becomes oxidized becomes reduced Methane Oxygen Carbon dioxide Water (reducing (oxidizing agent) agent) © 2014 Pearson Education, Inc. Oxidation of Organic Fuel Molecules During Cellular Respiration . During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced becomes oxidized becomes reduced © 2014 Pearson Education, Inc. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain . In cellular respiration, glucose and other organic molecules are broken down in a series of steps . Electrons from organic compounds are usually first transferred to NAD+, a coenzyme . As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration . Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP © 2014 Pearson Education, Inc. 6 Figure 9.4—NAD+ as an electron shuttle 2 e− + 2 H+ 2 e− + H+ + NAD NADH H+ Dehydrogenase Reduction of NAD+ 2[H] H+ (from food) Oxidation of NADH Nicotinamide Nicotinamide (oxidized form) (reduced form) © 2014 Pearson Education, Inc. How does NAD+ trap electrons from glucose and other organic molecules? • Enzymes called dehydrogenases remove a pair of hydrogen atoms (2 electrons & 2 protons) from the substrate (e.g., glucose), thereby oxidizing it. • The enzyme delivers the 2 electrons along with 1 proton to its coenzyme, NAD+ • The other proton is released as a hydrogen ion (H+) dehydrogenase © 2014 Pearson Education, Inc. NADH passes the electrons to the electron transport chain . Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction . O2 pulls electrons down the chain in an energy- yielding tumble . The energy yielded is used to regenerate ATP © 2014 Pearson Education, Inc. 7 Figure 9.5—An introduction to electron transport chains H2 + ½ O2 2 H + ½ O2 Controlled release of 2 H+ + 2 e− energy ATP G G ATP Explosive release ATP Free energy, energy, Free Free energy, energy, Free 2 e− ½ O 2 H+ 2 H2O H2O (a) Uncontrolled reaction (b) Cellular respiration © 2014 Pearson Education, Inc. Mitochondria: Chemical Energy Conversion . Mitochondria are in nearly all eukaryotic cells . They have a smooth outer membrane and an inner membrane folded into cristae . The inner membrane creates two compartments: intermembrane space and mitochondrial matrix . Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix . Cristae present a large surface area for enzymes that synthesize ATP © 2014 Pearson Education, Inc. Figure 6.17—The mitochondrion: site of cellular respiration Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix 0.1 µm © 2014 Pearson Education, Inc. 8 The Stages of Cellular Respiration: A Preview . Harvesting of energy from glucose has three stages: . Glycolysis (breaks down glucose into two molecules of pyruvate) . The citric acid cycle (completes the breakdown of glucose) . Oxidative phosphorylation (accounts for most of the ATP synthesis) © 2014 Pearson Education, Inc. Figure 9.6—An overview of cellular respiration (step 1) Electrons via NADH GLYCOLYSIS Glucose Pyruvate CYTOSOL MITOCHONDRION ATP Substrate-level © 2014 Pearson Education, Inc. Figure 9.6—An overview of cellular respiration (step 2) Electrons Electrons via NADH via NADH and FADH2 GLYCOLYSIS PYRUVATE OXIDATION CITRIC ACID Glucose Pyruvate Acetyl CoA CYCLE CYTOSOL MITOCHONDRION ATP ATP Substrate-level Substrate-level © 2014 Pearson Education, Inc. 9 Figure 9.6—An overview of cellular respiration (step 3) Electrons Electrons via NADH via NADH and FADH2 GLYCOLYSIS PYRUVATE OXIDATIVE OXIDATION CITRIC PHOSPHORYLATION ACID Glucose Pyruvate Acetyl CoA CYCLE (Electron transport and chemiosmosis) CYTOSOL MITOCHONDRION ATP ATP ATP Substrate-level Substrate-level Oxidative © 2014 Pearson Education, Inc. BioFlix: Cellular Respiration © 2014 Pearson Education, Inc. Oxidative vs. Substrate-level Phosphorylation . The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions . Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration . A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation . In total, for each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of ATP © 2014 Pearson Education, Inc. 10 Figure 9.7—Substrate-level phosphorylation Enzyme Enzyme ADP P Substrate ATP Product © 2014 Pearson Education, Inc. Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate . Glycolysis (“sugar splitting”) breaks down glucose into two molecules of pyruvate . Glycolysis occurs in the cytoplasm and has two major phases . Energy investment phase . Energy payoff phase . Glycolysis occurs whether or not O2 is present © 2014 Pearson Education, Inc. Figure 9.8—The energy Energy Investment Phase input and output of Glucose glycolysis 2 ATP used 2 ADP + 2 P Energy Payoff Phase 4 ADP + 4 P 4 ATP formed + + 2 NAD + 4 e− + 4 H 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net Glucose 2 Pyruvate + 2 H2O 4 ATP formed − 2 ATP used 2 ATP 2 NAD+ + 4 e− + 4 H+ 2 NADH + 2 H+ © 2014 Pearson Education, Inc. 11 Figure 9.9—A closer look at glycolysis GLYCOLYSIS: Energy Investment Phase ATP Glucose Fructose Glucose 6-phosphate 6-phosphate ADP Hexokinase Phosphogluco- isomerase 1 2 © 2014 Pearson Education, Inc. Figure 9.9 (cont.)—A closer look at glycolysis GLYCOLYSIS: Energy Investment Phase
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