Bio manual 06 - OKALOOSA SCHOOLS



7____________________________________________________________________________________________HOW CELLS RELEASE chemical energyChapter Outline7.1 RISKY BUSINESS7.2 overview of carbohydrate Breakdown pathways7.3 Glycolysis—SUGAR Breakdown BEGINS7.4 second stage of aerobic RespirationAcetyl-CoA FormationThe Krebs Cycle7.5 aerobic respiration’s big energy payoff7.6 fermentation7.7 Alternative Energy Sources in food Energy From Dietary MoleculesComplex carbohydratesFatsProteinsRISKY BUSINESS (revisited)SUMMARYSelf-Quiz data analysis ACTIVITIEScritical thinkingLearning Objectives7.1 Examine the role of mitochondria in the process of aerobic respiration.7.2 Differentiate between aerobic respiration and anaerobic fermentation pathways involved in the production of adenosine triphosphate from carbohydrates.7.3 Outline the stages of glycolysis using a diagram.7.4 Analyze the second stage of aerobic respiration which includes acetyl-CoA formation and the Krebs cycle.7.5 Examine the five stages involved in the final stage of aerobic respiration using a diagram.7.6 Examine the two types of fermentation pathways: alcoholic fermentation and lactate fermentation.7.7 Examine the different types of food molecules that are used by cells to produce energy through aerobic respiration.Key Termsaerobicaerobic respirationalcoholic fermentationanaerobicfermentationglycolysisKrebs cyclelactate fermentationpyruvatesubstrate-level phosphorylationLecture Outline 7.1 Risky Business A.Mitochondria are the organelles responsible for releasing the energy stored in foods.1.In Friedreich’s ataxia, too much iron in the mitochondria causes an accumulation of free radicals that attack valuable molecules of life.B.Proper or improper functioning of mitochondria is the difference between health and disease.7.2Overview of Carbohydrate Breakdown PathwaysA.ATP is the prime energy carrier for all cells, both autotrophic and heterotrophic.B.Aerobic Respiration1.Aerobic respiration (with oxygen) is the main energy-releasing pathway leading to ATP formation in eukaryotes; it occurs in the mitochondria.2.Every cell begins its energy-releasing pathways with glycolysis, which occurs in the cytoplasm and produces two molecules of pyruvate.C.Overview of Aerobic Respiration1.Three series of reactions are required for aerobic respiration.a.Glycolysis is the breakdown of glucose to pyruvate; small amounts of ATP are generated.b.The Krebs cycle degrades pyruvate to carbon dioxide and water, ATP is produced, and NAD and FAD accept H+ ions and electrons to be carried to the electron transfer chain.c.Electron transfer phosphorylation processes the H+ ions and electrons to generate high yields of ATP; oxygen is the final electron acceptor. D. Anaerobic Fermentation Pathways 1. Many bacteria, archea, fungi, and protists undergo fermentation to release energy from carbohydrates.a. Fermentation is an anaerobic (without oxygen) process that occurs in the cytoplasm.b. Anaerobic respiration is not as efficient as aerobic processes. 2. Fermentation begins with glycolysis.3. Electron transport chains do not occur in this process. 7.3Glycolysis—Sugar Breakdown BeginsA.Enzymes in the cytoplasm catalyze several steps in the breakdown of a six-carbon sugar glucose into two molecules of pyruvate, a three-carbon sugar.B.Glycolysis begins as energy-requiring reactions.C. Glycolysis continues as energy-releasing reactions.D. The end products of glycolysis are (for each glucose molecule): two pyruvates, two ATPs (net gain), and two NADH. 7.4Second Stage of Aerobic RespirationA.Acetyl-CoA Formation1.As each pyruvate enters the mitochondria, one carbon is removed and attaches to oxygen, forming carbon dioxide; the two-carbon fragment remaining joins coenzyme A to form Acetyl-CoA. 2.Two NAD+ are reduced.B.The Krebs Cycle1. Each three-carbon Acetyl-CoA molecule enters the Krebs cycle separately and joins oxaloacetate, already present from a previous “turn” of the cycle.2.H+ and e– are transferred to NAD+ and FAD to become NADH and FADH2, respectively; important potential energy for the cell comes from the eight NADH and two FADH2 coenzyme molecules produced during the Krebs cycle.3.Two molecules of ATP are produced by substrate-level phosphorylation.4.Most of the molecules are recycled to conserve oxaloacetate for continuous processing of acetyl-CoA.5.Carbon dioxide is released as a by-product.7.5 Aerobic Respiration’s Big Energy PayoffA.Electron Transfer Phosphorylation1.NADH and FADH2 give up their electrons to transfer (enzyme) systems embedded in the mitochondrial inner membrane.2.Oxygen joins with the “spent” electrons from the glucose molecule and H+ to yield water. a.Without oxygen, electrons back up the electron transfer chains, and no H+gradients form. b.No gradient means no ATP; complex cells cannot survive long without enough ATP for their processes. B.Summing Up: The Energy Harvest1.Electron transfer yields 32 ATPs, glycolysis yields two ATPs, and Krebs yields two ATPs for a grand total of 36 ATPs per glucose molecule.2.Normally, for every NADH produced within the mitochondria and processed by the electron transfer chain, three ATP are formed; FADH2 yields two ATPs. a.In most cells (skeletal, brain), NADH from the cytoplasm cannot enter the mitochondrion and must transfer its electrons to FAD, yielding two ATP (for a total of 36). b.However in the liver, heart, and kidney cells, NAD+ accepts the electrons to yield three ATP; two NADH are produced per glucose giving a total yield of 38 ATP.7.6 Fermentation A.Anaerobic pathways operate when oxygen is absent (or limited); pyruvate from glycolysis is metabolized to produce molecules other than acetyl-CoA.B.Two Fermentation anisms that carry on fermentation (fermenters) are diverse; many die when exposed to oxygen, while others use oxygen but switch when it becomes scarce.2.Fermentation yields enough energy for many single-celled anaerobic organisms and is sufficient for some aerobic cells when oxygen levels drop, but it is insufficient for large, multicelled organisms.C.Alcoholic Fermentation1.Fermentation begins with glucose degradation to pyruvate.2.Cellular enzymes convert pyruvate to acetaldehyde, which then accepts electrons from NADH to become alcohol.3Yeasts are valuable in the baking industry (carbon dioxide by-product makes dough “rise”) and in alcoholic beverage production.D.Lactate Fermentation1.Certain bacteria (as in milk) and muscle cells have the enzymes capable of converting pyruvate to lactate.2.No additional ATP beyond the net two from glycolysis is produced, but NAD+ is regenerated. 3. When muscle cells are very active, they convert to producing lactate temporarily. a. Slow-twitch muscle fibers (dark red) support steady, prolonged activity because they have many mitochondria making large quantities of ATP. b. Fast-twitch muscle fibers (light color) have few mitochondria and produce small amounts of ATP by lactate fermentation, supporting quick, non-sustained demands for energy.7.7Alternative Energy Sources in plex Carbohydrates1.After eating a meal, glucose is absorbed into the blood.a.Insulin levels rise, causing greater uptake of glucose by cells for entry into glycolysis.b.Excess glucose is converted into glycogen for storage in muscles and the liver.2.Between meals blood glucose levels fall.a.The hormone glucagon prompts liver cells to convert glycogen back to glucose.b.Glycogen levels are adequate but can be depleted in 12 hours.B.Fats1.Excess fats (including those made from carbohydrates) are stored away in cells of adipose tissue.2.Fats are digested into glycerol, which enters glycolysis, and fatty acids, which enter the Krebs cycle.3.Because fatty acids have many more carbon and hydrogen atoms, they are degraded more slowly and yield greater amounts of ATP.4.Excess glucose can be converted to fat by a diversion of acetyl-CoA into a pathway that synthesizes fatty acids.C.Proteins 1.Amino acids are released by digestion and travel in the blood.2.After the amino group is removed, the amino acid remnant is fed into the Krebs cycle.7.8 Risky Business (Revisited)A. Approximately 1 in every 5,000 people has a mitochondrial disease.1. Problems with mitochondrial functions may be responsible for additional disease, such as Alzheimer’s and Parkinson’s diseases.2. Researchers are more apt to try to cure diseases that affect more individuals.Suggestions for Presenting the Material?Stress the elegance of the cycle that connects photosynthesis and aerobic respiration. The products of photosynthesis are the reactants of aerobic respiration, and the products of aerobic respiration are the reactants of photosynthesis. How has man offset the natural balance of this cycle??The critical role of ATP must be emphasized. Distinguish clearly between the transfer of energy from carbohydrates to ATP (this chapter) and the synthesis of the ATP molecule (Chapter 6).?The material in this chapter is most easily and logically presented by skillful use of the figures on the overhead transparencies or slides.a.Begin with the flowchart of glycolysis (aerobic respiration), the Krebs cycle, and electron transfer. Point out the entry molecules, exit molecules, and key intermediates as well as the total energy yield (36 ATPs).b.Next, examine the graphics that depict more of the details of glycolysis, Krebs cycle, and electron transfer.?As you progress deeper into the pathway discussions, it is advisable to refer frequently to the overview graphic so that you keep the “big picture” in mind. You will need to indicate that fermentation begins with glucose and proceeds from pyruvate.?The synthesis of ATP by electron transfer phosphorylation is perhaps beyond the scope of some courses for nonscience majors. It may be omitted without detriment to the overall presentation.?Summing up the total energy yield is important. ?You can emphasize the roles of other foods (proteins and lipids) and their relationship to carbohydrates by following the arrows of Figure XX. This especially appeals to students interested in nutrition.?Emphasize that plants do carry on aerobic respiration. Many students have the mistaken idea that plants only photosynthesize.?Have students work on learning the reactants and products for each step of cellular respiration first. For example, glucose and two ATPs are the reactants for glycolysis; two pyruvates and four ATPs are the products. Once they have the reactants and products learned the intermediate reactants are easier to learn and understand.?Stress to students the importance of knowing the processes rather than memorizing all the various reactions.?Although the focus in this chapter is the generation of ATP, you may wish to explain to your students that another major function of respiration is the production of intermediates for biosynthetic reactions.?Design an exercise for the class where you divide the class into team A and team B. Name a characteristic of glycolysis, the Krebs cycle, or electron transfer phosphorylation. Whichever team guesses the correct category of the three, scores a point. Make the winning team a congratulatory certificate! Perhaps in the spirit of competition, the students will master the specific details of each process.?Often students get so caught up in learning the processes, they miss the big picture. Don’t miss the forest for the trees. Keep repeating to students at every opportunity that the entire purpose of all the steps of anaerobic respiration, fermentation, and aerobic respiration is conversion of stored energy into usable energy. Classroom and Laboratory Enrichment?Show a video on cellular respiration.?Demonstrate a computer simulation whereby basal metabolism rate (BMR) is calculated by measuring oxygen consumption.?Select several persons who differ in physical stature and exercise conditioning. Allow them to exercise vigorously for several minutes; then determine heart rate and the length of time before breathing rate returns to normal (indicates extent of oxygen debt).Explain the purpose of lactic acid in muscle fatigue. Be sure to mention that once the oxygen debt has been repaid, the lactic acid breaks down into the harmless byproducts water and carbon dioxide, and physical activity can resume.?Explain the difference between slow-twitch and fast-twitch muscles by comparing marathon runners and sprinters.? Flow-chart the steps of cellular respiration in class, stressing the reactants and products of each step.?Ask an exercise physiologist to talk to the class about the effect(s) of exercise on body metabolic rate.Discuss some animal examples of “red” and “white” types of muscles. A goose is an animal that seems to have almost unlimited endurance. If we cooked a goose for dinner, it would contain primarily dark meat. On the other hand, much of the tuna fish’s meat is light in color, representing its ability to move in quick spurts of rapid movement.?If there is a brewery or winery nearby, arrange for a field trip. Brew masters and winemakers generally are happy to conduct a tour through the facilities and explain the processes involved.Perform Activity 1 on the following website, , which provides a fermentation experiment involving yeast. Classroom Discussion Ideas?Certain diseases more common in the elderly have been tied to mitochondrial defects. Could mitochondrial degradation be a part of normal aging? How might you detect this in patients??Tell how the measurement of oxygen consumption by a human patient is related to metabolic rate.?In Luft’s syndrome the mitochondria are not producing sufficient amounts of ATP. What series of reactions could be most responsible for the deficiency? What are some other conditions that are thought to involve mitochondrial malfunction? ?Mitochondria are critical for normal metabolism. From which parent did each human being’s original mitochondria come from at conception??Why are so many diseases attributed to defective mitochondria?Additional Ideas for Classroom Discussion?Table wines, those that have not been fortified, have an alcoholic content of about 10–12 percent. What factors could limit the production of alcohol during fermentation? Is it self-limiting, or do the vintners have to stop it with some additive??Your text lists two types of fermentation: one leads to alcohol, the other to lactate. Which occurs in yeasts and why? Which pathway is reversible? What would be the consequences of nonreversible lactate formation in muscle cells??Yeast is added to a mixture of malt, hops, and water to brew beer—a product in which alcohol and carbon dioxide are desirable! Why is yeast added to bread dough??What happens to lactate produced during periods of intense muscle activity? Why is it important that the lactate is broken down quickly??What effect do large amounts of lactic acid have on muscle tissue??Analyze the simple equation for cellular respiration by telling exactly at what place in the aerobic metabolism of glucose each item in the equation is a participant.?Think about which parts of a chicken are “dark meat.” Considering the mitochondrial content of dark versus white meat, why does this make sense??What is “metabolic water”??Why is fermentation necessary under anaerobic conditions? That is, why does the cell convert pyruvate to some fermentation product when it does not result in any additional ATP production??What is the benefit of lactate fermentation to our bodies? What happens if we fail to “repay” our oxygen debt?How Would You Vote? Classroom Discussion Ideas?Monitor the voting for the online question. One’s response to this question depends on whether you have great compassion for humankind or are more interested in successful business ventures. Obviously, pharmaceutical companies are in business to make money—lots of money. Therefore, they cannot profitably invest time and money in developing a drug/treatment for a small number of persons who will be grateful, but not make the company rich. The only alternative is for the government to give researchers and companies financial incentives, such as tax breaks, to pursue such research.One additional factor to keep in mind is that discoveries made while investigating “orphan” diseases (those affecting only a small amount of patients) can ultimately provide useful information for the study of other conditions. For example, if a researcher were investigating Friedreich’s ataxia, inroads might be forged in the treatment of other diseases that could be related to mitochondrial malfunctions (e.g., Alzheimer’s and Parkinson’s diseases). This exact scenario has occurred in the study of seizure disorders.Term Paper Topics, Library Activities, and Special Projects?Rotenone is a fish poison and insecticide. Its mode of action is listed on container labels as “respiratory poison.” Research exactly where and how it disrupts cellular respiration.?Prepare a fermentation vat with grape juice and yeast (don’t seal it!). Allow the process to proceed for a few days, then strain the fluid into a flask and distill it. What gas is produced during fermentation? What product distills at 78.5°C??Certain flour beetles and clothes moths can live in environments where exogenous water is virtually unobtainable, yet they thrive. What are the mechanisms they use for the synthesis and retention of water?How is it possible that some organisms can survive in both aerobic and anaerobic environments? Make a list of some of these organisms. Do any of these serve as health risks to humans??Investigate obligate anaerobes. Why can’t these organisms convert energy aerobically??Use diagrams to show how radioactive carbon-14 in glucose fed to rats could end up in body fat and proteins.?Because ATP is the direct source of energy for body cells, why not bypass the lengthy digestion and cellular metabolism processes necessary for carbohydrate breakdown and eat ATP directly?Investigate how the liver stores glucose as glycogen. How are these reactions reversible?Which byproducts of cellular metabolism are disposed of in the urine? Can an examination of urine determine any metabolic disorders??Damaged, swollen cans of food should be thrown away because of the danger that they have been infected with botulism. Investigate this pathogen and how it grows in such an environment.?Hydrogen cyanide is the lethal gas used in gas chambers. How does it cause death?Possible Responses to Critical Thinking Questions1.Altitude sickness results from a lack of oxygen, but more specifically, it results from the deficiency of oxygen needed to “pull” the train of electrons along the electron transfer chain, which provides the energy necessary to produce ATP. This would explain why the symptoms of altitude sickness would mimic those of cyanide poisoning, namely the inability to produce enough ATP to power the muscle cells necessary for breathing and pumping blood.2.Prokaryotes use the plasma membrane for electron transfer phosphorylation. 3. The journey of the bar-tailed godwit is indeed an amazing feat! This is accomplished by the majority of the flight muscles being of the dark meat variety. The darker color of the muscle is due to an abundance of myoglobin, which stores oxygen. This type of muscle is designed for prolonged activity due to its better endurance level.Possible Responses to Data Analysis Exercise QuestionsThe disease Tetralogy of Fallot (FT) is characterized by low oxygen levels and subsequent mitochondrial damage. The abnormality in this study that was most strongly associated with TF was the number of mitochondria.The percentage of TF patients that had mitochondria that were abnormal in size was 25 percent.From the data provided, it appears that those patients that have both abnormal numbers and shapes of mitochondria are the most affected by the disease. ................
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