Chapter 8: Harvesting Energy: Glycolysis and Cellular RespirationATP is the Universal Energy Source- Photosynthesizers get energy from the sun- Animals get energy 2nd or 3rd hand from plants or other organisms- Regardless, the energy is converted to the chemical bond energy of ATPMain Types of Energy-Releasing Pathways- Anaerobic pathwayso Evolved firsto Don’t require oxygeno Starts with glycolysis in cytoplasmo Completed in cytoplasm- Aerobic pathwayso Evolved latero Require oxygeno Starts with glycolysis in cytoplasmo Completed in mitochondriaoHow Do Cells Obtain Energy?- Most cellular energy is stored in the chemical bonds of energy-carrier molecules likeadenosine triphosphate (ATP)- Cells break down glucose in two stageso 1. Glycolysis: liberates a small quantity of ATPo 2. Cellular respiration: produces far more ATPPhotosynthesis Provides the Energy Released by Glycolysis and Cellular RespirationThe Role of Coenzymes for Cellular Respiration- Small molecules associated with an enzyme that participates in enzymatic catalysisCYTOPLASMGlycolysisElectron Transfer PhosphorylationKrebsCycleATPATP2 CO24 CO2232water2 NADH8 NADH2 FADH22 NADH2 pyruvatee- + H+e- + oxygen(2 ATP net)glucoseTypical Energy Yield: 36 ATPe-e- + H+e- + H+ATPH+e- + H+ATP24***MITOCHONDRIA6- NAD+, FAD, NADH, FADH2 are examples- NAD+ and FAD, accept electrons and hydrogen to become NADH & FADH2- Deliver electrons and hydrogen to the electron transfer chainOxidation versus Reduction- Oxidation refers to the loss of electronso When a molecule becomes oxidized, it loses an electron(s) and becomes more positively chargedo Na Na+ + e- Reduction refers to the gain of electronso When a molecule becomes reduced, it gains an electron(s) and becomes more negatively chargedo F + e F-- Glucose (C6H12O6) is a key energy-storage moleculeo All cells metabolize glucose for energyo In humans, energy is stored as long chains of glucose, called glycogen, or as fato These storage molecules are converted to glucose to produce ATP for energy harvestingoAn overview of glucose breakdown- The first stage of glucose breakdown is glycolysiso Begins by splitting glucose (a 6-carbon sugar) into two molecules of pyruvate(a 3-carbon sugar)o 2 ATP molecules are produced in glycolysiso Glycolysis proceeds in the same way under aerobic (with oxygen) or anaerobic (without oxygen) conditionso Glycolysis occurs in the cytoplasm- The second stage of glucose breakdown is cellular respiration and occurs when oxygen is availableo In this stage, 2 pyruvate molecules produced by glycolysis are broken down into 6 carbon dioxide molecules and 6 water moleculeso For every two pyruvate molecules, an additional 34 or 36 ATP molecules are generatedo Occurs in mitochondria, organelles specialized for the aerobic breakdown ofpyruvate- If oxygen is not available, the second stage of glucose breakdown is fermentationo Does NOT produce any ATPo Instead, pyruvate remains in the cytoplasm and is converted into lactate or ethanol + CO2- The overall equation for the complete breakdown of glucose is:o C6H12O6 + 6 O2 6 CO2 + 6 H2O + ATP + heat- A summary of Glucose BreakdownoEfficiency of Aerobic Respiration- Efficiency is only 39% (solar cells?)- Sounds really low, but really it is not- Most energy is lost as heatWhat happens during Glycolysis?- Glycolysis has two parts, each with several stepso 1. Glucose activation: these are the energy investment steps required to invest a small amount of energyo 2. Energy extraction: these are the energy harvesting steps releasing energy- Summary of glycolysiso Each molecule of glucose is broken down to two molecules of pyruvateo A net of two ATP molecules and two NADH (high-energy electron carrier) areformedoWhat happens during Cellular Respiration?- Cellular respiration in eukaryotic cells occurs in mitochondria in three stageso 1. Pyruvate is broken down into the mitochondrial matrix, releasing energy and CO2o 2. High-energy electrons travel through the electron transport chaino 3. ATP is generated by chemiosmosis- First, pyruvate is broken down in the mitochondrial matrix, releasing energy & CO2o In eukaryotes, cellular respiration occurs within mitochondria, organelles with two membraneso Glucose is first broken down into pyruvate, through glycolysis, in the cell cytoplasmIf O2 is availablematrix (fluid)o Pyruvate is next transported into the mitochondrion matrix, where further breakdown occurs in 2 stages: The formation of acetyl coenzyme A (acetyl CoA) The Krebs Cycleo During the mitochondrial reactions, CO2 is generated as a waste producto CO2 diffuses out of cells and into the blood, which carries it to the lungs, where it is exhaledo Reactions in the Mitochondrial Matrix- In the second stage of cellular respiration, high-energy electrons travel through the electron transport chaino These high-energy electrons jump from molecule to molecule in ETC, losing small amounts of energy at each stepo This energy is harnessed to pump H+ from the matrix and into the intermembrane space, producing concentration gradient of H+o The buildup of H+ in the intermembrane space is used to generate ATP during chemiosmosiso At the end of the ETC, the energy-depleted electrons are transferred to oxygen, which acts as an electron acceptoro Energy-depleted electrons, oxygen, and hydrogen ions combine to form watero ATP generation continues only when there is a steady supply of oxygeno The Electron Transport Chain:2o- The third stage of cellular respiration generates ATP by chemiosmosiso Chemiosmosis is the process by which energy is first used to generate a gradient of H+ and then captured in the bonds of ATP as H+ flow down its gradiento The H+ ions flow across the membrane through the ATP synthase channels, generating ATP from ADP + phosphateo The flow of H+ through the synthase channel provides the energy to synthesize 32 or 34 molecules of ATP for each molecule of glucoseo The newly formed ATP leaves the mitochondria and enters the cytoplasm, where it provides the energy needed by the cell- The Energy Sources and ATP Harvest from Glycolysis and Cellular Respiration-What happens during Fermentation?- Why is fermentation necessary?o For glycolysis to continue, the NAD+ used to generate NADH must constantly be regeneratedo If NAD+ was depleted, glycolysis would stop, energy production would cease, and organisms would dieo There are 2 types of fermentation to regenerate NAD+ Lactic acid fermentation produces lactic
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