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CELLULAR RESPIRATION CHAPTER 9 9-1 Chemical Pathways Chemical Energy and Food PHOTOSYNTHESIS 6 CO 6H O 2 + _________ 2 ___________ + ___________ C6H12O6 + __________ 6O2 →_______________ CELLULAR RESPIRATION C6H12O6 + _________ 6O2 _____________ 6 CO2 + __________ 6 H2O + __________ →________ The two equations are exact opposites! Comparing Photosynthesis & Cellular Respiration: • Which type(s) of organisms carry out photosynthesis? Autotroph Heterotroph • Which type(s) of organisms carry out cellular respiration? Autotroph Heterotroph Overview of Cellular Respiration • Cellular respiration is the process that releases energy from food in the presence of oxygen. • If oxygen is available, organisms can obtain energy from food by a process called cellular respiration. • The summary of cellular respiration is presented below. 6 O2 + C6H12O6 6 CO2 + 6 H2O + Energy (ATP) Structure of the Mitochondria: Chemical Energy and Food • Cellular respiration happens slowly and in many steps. • If all the energy was release in one step… Most would be lost as light and heat! • Cellular respiration breaks down glucose molecules and banks their energy in ATP Chemical Energy and Food • Amount of heat it takes to raise 1 gram of water 1o Celsius = calorie • Unit for measuring energy in food = Calorie • 1 Calorie = 1 kilocalorie = 1,000 calories Comparing Photosynthesis & Cellular Respiration Photosynthesis Cellular Respiration Function Produces food (chemical energy) for the plant (glucose C6H12O6) Produces chemical energy (ATP) for the cell Location Chloroplast Mitochondria Reactants Water (H2O), Carbon dioxide (CO2) and sunlight Oxygen (O2) and Glucose (C6H12O6) Products Oxygen (O2) and Glucose (C6H12O6) Water (H2O), Carbon dioxide (CO2) and energy (ATP) Energy Consumption - Virtual Cell Animation (4:41) H2O Compare Photosynthesis to Cellular Respiration CO2 Chloroplast Light Energy NADP+ ADP + P LIGHT REACTIONS (in thylakoids) CALVIN CYCLE (in stroma) ATP NADPH How Cells Obtain Energy (14 min) O2 NADH High-energy electrons carried by NADH NADH FADH2 and CITRIC ACID CYCLE GLYCOLYSIS Glucose Pyruvate OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Mitochondrion Cytoplasm ATP Substrate-level phosphorylation CO2 ATP CO2 Substrate-level phosphorylation ATP Oxidative phosphorylation Sugar (C6H12O6) An Overview of Cellular Respiration: Stages of Cellular Respiration The three main stages of cellular respiration are 1. Glycolysis 2. Krebs cycle 3. Electron transport chain. Oxygen and Energy • Glycolysis is an ANAEROBIC processes. It does not directly require oxygen, nor does it rely on an oxygen-requiring process to run. • Glycolysis is still considered part of cellular respiration. • Glycolysis takes place in the cytoplasm of a cell. Glycolysis Overview - Virtual Cell Animation (3:00) Oxygen and Energy • Pathways of cellular respiration that require oxygen are called AEROBIC. • The Krebs cycle and electron transport chain are both aerobic processes. • Both processes take place inside the mitochondria. Citric Acid Cycle An Overview (3:17) Electron Transport Chain (3:48) Overview of Cellular Respiration Occurs in three main stages: Stage 1 Stage 1: Glycolysis • • Occurs in the cytoplasm Breaks down glucose into pyruvate, producing a small amount of ATP Stage 2 Stage 2: The Citric Acid Cycle (Krebs cycle) • • • Takes place in the mitochondria Stage 3 Completes breakdown of glucose, produces a small amount of ATP Provides third stage of cell respiration with electrons Overview of Cellular Respiration Stage 3: Oxidative phosphorylation (ETC) • 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 Stage 3 Understanding Oxidation and Reduction •Oxidation is the loss of electrons; electrons are removed from hydrogen atoms contained in glucose. •Reduction is the gain of electrons; oxygen atoms accept hydrogen and electrons forming water H2O. • Remember: • OIL RIG (Oxidation Is Loss, Reduction Is Gain) • LEO the lion goes GER (Lose Electrons – Oxidation) (Gain Electrons – Reduce) Electron Carriers (enzymes) Involved •NAD+ (Nicotinamide adenine dinucleotide) Accepts H+ to become NADH •FAD (Flavin adenine dinucleotide) Accepts 2H+ to become FADH2 Overview of Cellular Respiration NADH High-energy electrons carried by NADH NADH FADH2 and Stage 1 Stage 3 Stage 2 OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) GLYCOLYSIS Glucose CITRIC ACID CYCLE Pyruvate Krebs Mitochondrion Cytoplasm ATP Substrate-level phosphorylation CO2 CO2 ATP ATP Substrate-level phosphorylation Oxidative phosphorylation 9.2 Glycolysis • • • • (Glykos = sweet, Lysis = split apart) The first step in cellular respiration = Glycolysis Happens in the CYTOPLASM outside the mitochondria Does not require oxygen, BUT it needs some energy to get it started. What molecule is going to supply the energy? ATP Glycolysis ________ ↓ GLUCOSE ___________ ATP → PYRUVIC ACID → 2 _____________ ↓ ATP ATP ATP NADH NADH ____________________ + _______________ PUT IN 2 ATP and GET BACK 4 ATP Net gain of 2 ATP and 2 NADH Glycolysis • Produces pyruvic acid (pyruvate – a 3 carbon compound) • Cell needs to invest some energy to get a higher return (2 ATP gained) • Occurs quickly, in miliseconds to respond to increased energy demand Glycolysis Reactions - Virtual Cell Animation (5:00) 9-2 The Krebs Cycle and Electron Transport Mitochondria Structure •Has a double membrane, with an intermembrane space between the two layers. •Cristae are folds of the inner membrane •The matrix is the innermost compartment, which is filled with a gel-like fluid. •Krebs Cycle occurs in the matrix of the mitochondria. The Krebs Cycle Carbon dioxide is lost to the atmosphere as waste ATP can be used directly to supply energy for the cell High energy electron carriers move into the ELECTRON TRANSPORT CHAIN The Krebs Cycle • During the Krebs cycle, the 2nd stage of cellular respirationpyruvic acid produced in glycolysis is broken down into carbon dioxide in a series of energyextracting reactions. • The Krebs cycle is also known as the citric acid cycle because citric acid is the first compound formed in this series of reactions. The Krebs Cycle • Pyruvic acid enters the mitochondria matrix • Pyruvic acid is converted into an intermediate 2 carbon molecule called Acetyl-CoA before entering the Krebs Cycle. • The Krebs cycle breaks down carbon compounds into carbon dioxide (waste), ATP, NADH, and FADH2 The Citric Acid Cycle The Reactions (4:13) The Krebs Cycle • Pyruvic acid from glycolysis enters the matrix, the innermost compartment of the mitochondrion. Kreb’s Cycle • Pyruvic acid from glycolysis enters the matrix • NAD+ accepts 2 highenergy electrons to form NADH. • One molecule of CO2 is also produced. • The remaining 2 carbon atoms react to form acetylCoA. Diagram by Riedell The Krebs Cycle • Acetyl-CoA combines with a 4-carbon molecule (oxaloacetic acid) to produce citric acid. The Citric Acid Cycle The Reactions (4:13) The Krebs Cycle • Citric acid is broken down into a 5-carbon compound and then a 4-carbon compound. • Two molecules of CO2 are released. • The 4-carbon compound can then start the cycle again by combining with acetyl-CoA. The Citric Acid Cycle The Reactions (4:13) KREBS CYCLE Krebs Cycle Animation-(select #3) KREBS CYCLE PRODUCES ____ ____ 3 ____ ____ 1 1 4 Electron Transport Chain • Enzymes (protein complexes) for the electron transport chain are located on the inner mitochondrial membrane. • Several complexes are called cytochromes. Electron Transport Chain (3:48) Electron Transport Chain •Electrons from NADH and FADH2 travel down the electron transport chain, between protein complexes to oxygen (final electron acceptor), which picks up H+ to form water NADH NAD + H + ATP 2e + Controlled release of energy for synthesis of ATP 2e 2 •Energy released by the redox reactions is used to pump H+ into the space between the mitochondrial membranes H 1 + 2 H2O Electron Transport Chain (2:00) O2 Chemiosmosis • In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes. • Drives the synthesis of ATP H+ H+ H+ H+ + Intermembrane space Inner mitochondrial membrane . H H+ Protein complex H+ Electron carrier FADH2 Electron flow NADH H+ H+ FAD NAD+ H+ 1O + 2 H+ 2 2 + Mitochondrial matrix ATP synthase H H+ H2O ADP Electron Transport Chain OXIDATIVE PHOSPHORYLATION + P ATP H+ Chemiosmosis Fermentation • Pyruvic acid moves to the next step • If there is no oxygen = anaerobic • If there is oxygen = aerobic Fermentation • Fermentation – process by which cells release energy in the absence of oxygen • Two types of fermentation: • Alcoholic Fermentation • Lactic Acid Fermentation Alcoholic Fermentation PYRUVIC ACID +_____ _______ + ALCOHOL CO NAD 2 →__________ + ______ + _____ • Happens when yeast makes bread dough rise, CO2 bubbles make air spaces in bread. (Alcohol evaporates during cooking) • Happens when: • Yeast make beer • Bacteria make wine Lactic Acid Fermentation PYRUVIC ACID +_____ _______ + LACTIC ACID NAD →______________ + ________ • Happens in muscles during exercise when body can’t get oxygen to tissues fast enough. • Lactic acid builds up in muscles causing soreness. • Bacteria use lactic acid fermentation to make: yogurt, cheese, sour cream, pickles, sauerkraut, kimchi The Totals • Cellular Respiration (aerobic: with oxygen) 1 glucose → 36 ATP • Fermentation (anaerobic: without oxygen) 1 glucose → 2 ATP Respiration Questions 1. 2. 3. 4. List the reactants and products of respiration List the three steps (stages) involved in respiration Name two electron carriers involved What step produces the most ATP Respiration Questions • 1. 2. 3. 4. In your group: See if you can write the chemical equation for respiration (inputs and outputs) What is the organelle in cells that is “releasing” energy during respiration? What primary molecule is energy being “released” from? How is the sun indirectly involved in respiration? Fermentation Questions 1. 2. 3. 4. 5. 6. List two types of fermentation List the reactants for both types of fermentation List the products for fermentation used to brew beer List the products for fermentation used to make yogurt What important molecule cycles back from fermentation to keep glycolysis going? What process starts fermentation? Krebs Cycle 1.___________ 2.___________ 7.________ 3.________ 4.________ 6.________ 5.________ Electron Transport Chain (ETC) H+ H+ H+ H+ + Intermembrane space H H+ Protein complex H+ Electron carrier . H+ H+ ATP synthase Inner mitochondrial membrane Electron flow FADH2 NAD+ NADH Mitochondrial matrix FAD H+ 1 O2 + 2 H+ 2 H+ H+ H2O Electron Transport Chain OXIDATIVE PHOSPHORYLATION ADP + ATP P H+ Chemiosmosis Cellular Respiration - Glycolysis, Krebs Cycle, ETC (6:00)