How Cells Harvest Chemical Energy Chapter 6 Introduction: How Is a Marathoner Different from a Sprinter? Individuals inherit various percentages of the two main types of muscle fibers, slow and fast The difference between the two is the process each uses to make Slow fibers make it aerobically using oxygen Fast fibers work anaerobically without oxygen Introduction: How Is a Marathoner Different from a Sprinter? The percentage of slow and fast muscle fibers determines the difference between track athletes Those with a large percentage of slow fibers make the best long-distance runners INTRODUCTION TO CELLULAR RESPIRATION Those with more fast fibers are good sprinters All of our cells harvest chemical energy () from our food
6.1 Photosynthesis and cellular respiration provide energy for life Energy is necessary for life processes These include growth, transport, manufacture, movement, reproduction, and others Energy that supports life on Earth is captured from sun rays reaching Earth through plant, algae, protist, and bacterial photosynthesis 6.1 Photosynthesis and cellular respiration provide energy for life Energy in sunlight is used in photosynthesis to make glucose from CO and H O with release of O Other organisms use the O and energy in sugar and release CO and H O Together, these two processes are responsible for the majority of life on Earth Sunlight energy ECOSYSTEM CO H O Photosynthesis in chloroplasts Cellular respiration in mitochondria +! +! O 6. Breathing supplies oxygen to our cells for use in cellular respiration and removes carbon dioxide Breathing and cellular respiration are closely related Breathing is necessary for exchange of CO produced during cellular respiration for atmospheric O Cellular respiration uses O to help harvest energy from glucose and produces CO in the process (for cellular work) Heat energy
O Breathing CO 6.3 Cellular respiration banks energy in molecules Lungs Cellular respiration transfers energy from the bonds in glucose to CO Bloodstream O Cellular respiration produces 38 molecules from each glucose molecule Other foods (organic molecules) can be used as a source of energy as well Muscle cells carrying out Cellular Respiration + O CO + H O + 6.5 Cells tap energy from electrons falling from organic fuels to oxygen The energy necessary for life is contained in the chemical bonds in organic molecules C 6 H 1 O 6 + 6 O Oxygen 6 CO Carbon dioxide + 6 H O Water + s Energy How do cells extract this energy?
6.5 Cells tap energy from electrons falling from organic fuels to oxygen Energy can be released from glucose by simply burning it The energy is dissipated as heat and light and is not available to living organisms 6.5 Cells tap energy from electrons falling from organic fuels to oxygen Cellular respiration is the controlled, stepwise breakdown of glucose Energy is released in small amounts that can be captured by cells and stored in 6.5 Cells tap energy from electrons falling from organic fuels to oxygen A cellular respiration equation is helpful to show the changes in hydrogen atom distribution loses its hydrogen atoms and is ultimately converted to CO At the same time, O gains hydrogen atoms and is converted to H O C 6 H 1 O 6 + 6 O Loss of hydrogen atoms (oxidation) Gain of hydrogen atoms (reduction) 6 CO + 6 H O + Energy ()
STAGES OF CELLULAR RESPIRATION AND FERMENTATION 6.6 Overview: Cellular respiration occurs in three main stages Stage 1: Glycolysis Glycolysis begins respiration by breaking glucose, a sixcarbon molecule, into two molecules of a three-carbon compound called pyruvate This stage occurs in the cytoplasm 6.6 Overview: Cellular respiration occurs in three main stages Stage : The citric acid cycle The citric acid cycle breaks down pyruvate into carbon dioxide and supplies the third stage with electrons This stage occurs in the mitochondria 6.6 Overview: Cellular respiration occurs in three main stages Stage 3: Oxidative During this stage, electrons are shuttled through the electron transport chain As a result, is generated through oxidative associated with chemiosmosis This stage occurs in the inner mitochondrion membrane
6.6 Overview: Cellular respiration occurs in three main stages During the transport of electrons, a concentration gradient of ions is formed across the inner membrane into the intermembrane space The potential energy of this concentration gradient is used to make by a process called chemiosmosis GLYCOLYSIS NADH High-energy electrons carried by NADH Pyruvate NADH CITRIC ACID CYCLE FADH and Mitochondrion OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) The concentration gradient drives through synthases and enzymes found in the membrane, and is produced Cytoplasm CO CO Inner mitochondrial membrane Substrate-level Substrate-level Oxidative 6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate In glycolysis, a single molecule of glucose is enzymatically cut in half through a series of steps to produce two molecules of pyruvate In the process, two molecules of NAD + are converted to two molecules of NADH, an electron carrier Two molecules of are produced ADP + P NAD +! NADH + Pyruvate
6.8 Pyruvate is chemically groomed for the citric acid cycle The pyruvate formed in glycolysis is transported to the mitochondria, where it is prepared for entry into the citric acid cycle 6.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH molecules With the help of CoA, the acetyl (two-carbon) compound enters the citric acid cycle Pyruvate NAD + NAD CoA 1 Acetyl coenzyme A 3 CO Coenzyme A At this point, the acetyl group associates with a fourcarbon molecule forming a six-carbon molecule The six-carbon molecule then passes through a series of redox reactions that regenerate the four-carbon molecule (thus the cycle designation) Acetyl CoA CoA CoA 6.10 Most production occurs by oxidative Oxidative involves electron transport and chemiosmosis and requires an adequate supply of oxygen CITRIC ACID CYCLE CO NADH and FADH and the inner membrane of the mitochondria are also involved FADH! FAD! 3 NAD + 3 NADH + 3 A ion gradient formed from all of the redox reactions of glycolysis and the citric acid cycle provide energy for the synthesis of! ADP +! P!
Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Protein complex of electron carriers Electron flow NADH NAD +! FADH Electron carrier FAD Electron Transport Chain 1! H O OXIDATIVE PHOSPHORYLATION O + ADP + P Chemiosmosis synthase 6.11 CONNECTION: Certain poisons interrupt critical events in cellular respiration There are three different categories of cellular poisons that affect cellular respiration The first category blocks the electron transport chain (for example, rotenone, cyanide, and carbon monoxide) The second inhibits synthase (for example, oligomycin) Finally, the third makes the membrane leaky to hydrogen ions (for example, dinitrophenol) Rotenone Cyanide, carbon monoxide Oligomycin 6.1 Review: Each molecule of glucose yields many molecules of DNP synthase Recall that the energy payoff of cellular respiration involves (1) glycolysis, () alteration of pyruvate, (3) the citric acid cycle, and (4) oxidative NADH FADH NAD +! FAD! 1 O + H O ADP + P The total yield of molecules per glucose molecule has a theoretical maximum of about 38 This is about 40% of a glucose molecule potential energy Additionally, water and CO are produced Electron Transport Chain Chemiosmosis
Cytoplasm Electron shuttle across membrane NADH NADH NADH (or FADH ) 6 NADH FADH Mitochondrion 6.13 Fermentation enables cells to produce without oxygen Fermentation is an anaerobic (without oxygen) energy-generating process GLYCOLYSIS Pyruvate Acetyl CoA CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) It takes advantage of glycolysis, producing two molecules and reducing NAD + to NADH + by substrate-level + by substrate-level + about 34 by oxidative The trick is to oxidize the NADH without passing its electrons through the electron transport chain to oxygen Maximum per glucose: About 38 6.13 Fermentation enables cells to produce without oxygen Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation NADH is oxidized to NAD + when pyruvate is reduced to lactate In a sense, pyruvate is serving as an electron sink, a place to dispose of the electrons generated by oxidation reactions in glycolysis ADP + P GLYCOLYSIS NAD + NADH Pyruvate NADH NAD + Animation: Fermentation Overview Lactate Lactic acid fermentation
6.13 Fermentation enables cells to produce without oxygen The baking and winemaking industry have used alcohol fermentation for thousands of years Yeasts are single-celled fungi that not only can use respiration for energy but can ferment under anaerobic conditions They convert pyruvate to CO and ethanol while oxidizing NADH back to NAD + ADP + P CO released GLYCOLYSIS Pyruvate NAD + NADH NADH NAD + Ethanol Alcohol fermentation 6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on Earth Glycolysis is the universal energy-harvesting process of living organisms So, all cells can use glycolysis for the energy necessary for viability The fact that glycolysis has such a widespread distribution is good evidence for evolution 6.15 Cells use many kinds of organic molecules as fuel for cellular respiration Although glucose is considered to be the primary source of sugar for respiration and fermentation, there are actually three sources of molecules for generation of Carbohydrates Proteins Fats
Food, such as peanuts Carbohydrates Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups G3P Pyruvate GLYCOLYSIS Acetyl CoA CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)