Science Notebook #4 9/30/14 10A Mr. Torres9.1 Cellular Respiration: An OverviewChemical Energy and FoodFood provides living things with the chemical building blocks they need to grow and reproduce.

Food molecules contain chemical energy that is released when its chemical bonds are broken.

Energy Releasing Pathways: Cellular Respiration, Anaerobic Respiration, and Fermentation.

Energy stored in food is expressed in units of calories. A calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. 1000 calories = 1 kilocalorie, or Calorie.Cells use all sorts of molecules for food, including fats, proteins, and carbohydrates. The energy stored in each of these molecules varies because their chemical structures, and therefore their energy-storing bonds, differ. (Glucose=4kcal per gram)Cells break down food molecules gradually and use the energy stored in the chemical bonds to produce compounds such as ATP that power the activities of the cell. Overview of Cellular RespirationIf oxygen is available, organisms can obtain energy from food by a process called cellular respiration. The summary of cellular respiration is presented below.In symbols: 6O2+C6H12O6+6CO2+6H2O+EnergyIn words: Oxygen + Glucose Carbon Dioxide + Water + EnergyThe cell has to release the chemical energy in food molecules (like glucose) gradually, otherwise most of the energy would be lost in the form of heat and light.Stages of Cellular RespirationThe three main stages of cellular respiration are glycolysis, the Krebs cycle, and the electron transport chain.Glycolysis produces only a small amount of energy. Most of glucoses energy (90%) remains locked in the chemical bonds of pyruvic acid at the end of glycolysis. During the Krebs cycle, a little more energy is generated from pyruvic acid.The electron transport chain produces the bulk of the energy in cellular respiration by using oxygen, a powerful electron acceptor. Oxygen and EnergyPathways 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.Glycolysis is an anaerobic process.It does not directly require oxygen, nor does it rely on an oxygen- requiring process to run.Glycolysis takes place in the cytoplasm of a cell.Comparing Photosynthesis and Cellular RespirationPhotosynthesis and cellular respiration are opposite processes.The energy flows in opposite directions. Photosynthesis deposits energy, and cellular respiration withdraws energy.The Reactants of cellular respiration are the products of photosynthesis and vice versa.6CO2 + 6H2O C6H12O6 + 6O2The release of energy by cellular respiration takes place in plants, animals, fungi, protists, and most bacteria.Energy capture by photosynthesis occur only in plants, algae, and some bacteria.9.2 The Process of Cellular RespirationGlycolysisGlycolysis is the first stage of cellular respiration and anaerobic respiration and it is the first step in fermentation.During Glycolysis, glucose is broken down into 2 molecules of the 3-carbon molecule pyruvic acid. Pyruvic acid is a reactant in the Krebs cycle.ATP and NADH are produced as part of the process.Phosphorylation and Cleavage of Glucose (Diagram)ATP Synthesis (Diagram)ATP ProductionThe cell deposits 2 ATP molecules into its account to get glycolysis going.Glycolysis then produces 4 ATP molecules, giving the cell a net gain of 2 ATP molecules for each molecule of glucose that enters glycolysis.During glycolysis, the electron carrier NAD+ (nicotinamide adenine dinucleotide) accepts a pair of high-energy electrons and becomes NADH.NADH carries the high-energy electrons to the electron transport chain, where they can be used to produce more ATP.2NADH molecules are produced for every molecule of glucose that enters glycolysis.Glucose 2Pyruvic acid +2ATP +2 NADHThe Advantages of GlycolysisGlycolysis produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increases.Glycolysis does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.Pyruvic acid from glycolysis enters the matrix, the innermost compartment of the mitochondrion.Formation of Acetyl-CoAA cofactor is a non-protein chemical compound that is required for the proteins biological activity.Cofactors can be subdivided into either one or more inorganic ions, or a complex organic or metalloorganic molecule called a coenzyme, most of which are derived from vitamins and from required organic nutrients in small amounts.Coenzymes are bound to enzyme active sites to aid with their proper functioning.The function of coenzymes is to transport groups between enzymes, chemical groups include hydride ions, phosphate groups and acetyl groups.Once pyruvic acid ends in the mitochondrial matrix. NAD+ accepts 2 high-energy electrons to form NADH. One molecule of CO2 is also produced.The remaining 2 carbon atoms react to form acetyl-CoA.The Krebs CycleDuring the Krebs cycle, the second stage of cellular respiration, pyruvic acid produced in glycolysis is broken down into carbon dioxide in a series of energy-extracting reactions.The Krebs cycle is also known as the citric acid cycle because citric acid is the first compound formed in this series of reaction.Citric Acid ProductionAcetyl-CoA combines with a 4-carbon molecule (oxaloacetate) to produce citric acid.Energy ExtractionCitric acid is broken down into a 5-carbon (a-ketoglutarate) compound and then a 4-carbon compound (succinyl-CoA)Two molecules of CO2 are released.The 4-carbon compound can then start the cycle again by combining with acetyl-CoAEnergy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2.For Each turn of the cycle, one ADP molecule is converted into ATP. ATP can directly power the cells activities.The electron carriers NAD+ and FAD each accept pairs of high-energy electrons to form NADH and FADH2.NADH and FADH, are used in the electron transport chain to generate ATP.Remember! Each molecule f glucose results in 2 molecules of pyruvic acid, which enter the Krebs cycle.So each molecule of glucose results in two complete turns of the Krebs cycle.Therefore, for each glucose molecules, 6CO2 molecules, 2 ATP molecules, 8NADH molecules, and 2 FADH molecules are produced.Electron Transport NADH and FADH, pass their high-energy electrons to electron carrier proteins in the electron transport chain. Ubiquinone, first electron acceptor. Cytochrome c: transfer electrons to molecular oxygen(O2)Energy generated by the electron transport chain is used to move H+ ions against a concentration gradient across the inner mitochondrial membrane and into the intermembrane space.ATP ProductionH+ ions pass back across the mitochondrial membrane through the ATP synthase, causing the ATP synthase molecule to spin.With each rotation, the ATP synthase attaches a phosphate to ADP to produce ATP.Electron TransportAt the end of the electron transport chain, the electrons combine with H+ ions and oxygen to form water.Energy TotalsIn the presence of oxygen, the complete breakdown of glucose through cellular respiration results in the production of 36 ATP molecules.This represents about 36 percent of the total energy of glucose. The remaining 64 percent is released as heat.The cell can generate ATP from just about any source, even though weve modeled it using only glucose.Complex carbohydrates are broken down into simple sugars like glucose.Lipids and proteins can be broken down into molecules that enter the Krebs cycle of glycolysis at one of several places.

9.3 FermentationFermentation Fermentation is the process by which energy can be released from food molecules in the absence of oxygen.Under anaerobic conditions, fermentation follows glycolysis.During fermentation, cells convert NADH produced by glycolysis back into the electron carrier NAD+, which allows glycolysis to continue producing ATP.Alcoholic FermentationYeast and a few other microorganisms use alcoholic fermentation that produces ethyl alcohol and carbon dioxide. This process is used to produce alcoholic beverages and causes bread dough to rise.Chemical equation:Pyruvic acid + NADH Alcohol + CO2 + NAD(+)Lactic Acid FermentationMost organisms, including humans, carry out fermentation using it a chemical reaction that converts pyruvic acid to Chemical Equation:Pyruvic acid + NADH Lactic acid + NAD(+) Quick EnergyCells normally contain small amounts of ATP produced during cellular respiration, enough for a few seconds of intense activity.Lactic acid fermentation can supply enough ATP to last about 90 seconds.However, extra oxygen is required to get rid of the lactic acid produced.Following intense exercise, a person will huff and puff for several minutes in order to pay back the built-up oxygen debt and clear the lactic acid from the body.Long-Term EnergyFor intense exercise lasting longer than 90 seconds, cellular respiration is required to continue production of ATP.Cellular respiration releases energy more slowly than fermentation does.The body stores energy in the form of the carbohydrate glycogen.Thee glycogen stores are enough to last for 15-20 minutes of activity. After that, the body begins to break down other stored molecules, including fats, for energy.