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1. Cellular RespirationLecture 6 http://upload.wikimedia.org

2. Much of the text material in the lecture notes is from our textbook, “Essential Biology with Physiology” by Neil A. Campbell, Jane B. Reece, and Eric J. Simon (2004 and 2008). I don’t claim authorship. Other sources were sometimes used, and are noted.

3. Outline • Intense exercise • Producers and consumers • Food web • Chemical cycle in ecosystems • Cellular respiration • Versatility of cellular respiration • Anaerobic effort • Fermentation in foods • Life on an anaerobic earth • Words and terms to know • Possible test items

4. Starting Line http://eerc.ra.utk.edu Running can require both aerobic and anaerobic effort.

5. Aerobic and Anaerobic • Muscles need a steady supply of oxygen to perform work and continue functioning. • The metabolism of muscle is ‘aerobic’ when the muscle cells receive an adequate supply of oxygen. • Breathing becomes faster and deeper as muscles work progressively harder. • The metabolism becomes ‘anaerobic’ when the demand for oxygen is greater than the body’s ability to deliver it.

6. Intense Exercise • In anaerobic conditions, muscles break-down glucose, producing lactic acid as a by-product. • If too much lactic acid builds-up, the burning sensation is accompanied by an inability of the muscles to function. • We will be discussing the metabolic pathways for aerobic and anaerobic work.

7. Skeletal Muscle Microscopic view http://www.ivy-rose.co.uk Muscle fiber http://www.brown.edu

8. The Longest Yards http://www.abbagav.com Endurance runners learn to stay within their aerobic limits until the final dash.

9. Solar Energy and Food • Food molecules are the storage of energy from the sun in an indirect form. • Animals rely on plants to convert the energy of sunlight to the chemical energy of sugars and other organic molecules. • Humans depend on plants for cotton, lumber, paper, and other products. • The conversion of solar energy to chemical energy (photosynthesis) will be discussed next week. http://solar-center.stanford.edu

10. Autotrophs and Heterotrophs • Most plants are autotrophs (self-feeders) that make all their organic matter from inorganic nutrients including carbon dioxide, water, and minerals from the soil. • Animals are heterotrophs (other-feeders) that cannot make organic molecules from inorganic ones—they must eat to obtain nutrients from food. • Heterotrophs depend on autotrophs for organic materials for growth and repair.

11. Producers and Consumers • Biologists refer to autotrophs as producers and heterotrophs as consumers. • Almost all ecosystems depend on sunlight and photosynthesis for food. • An example of a food web in a forest ecosystem is shown on the next slide.

12. Food Web http://www.biologycorner.com

13. Human ‘Food Web’ http://www.nyitotkert.com

14. Photosynthesis and Cellular Respiration • Photosynthesis is dependent upon carbon dioxide absorbed by leaves, and water absorbed by roots. • The chloroplasts found in plants use CO2 and H2O to form glucose and O2. • Animals and plants use the glucose and O2 to obtain chemical energy through cellular respiration. • Cellular respiration produces the by-products, CO2 and H2O, completing the chemical cycle. The oxygen present in the atmosphere is a result of photosynthesis, and it enabled life as we know it to develop and flourish. The atmosphere is not very deep, and most humans live at elevations of 10,000 feet our less.

15. Shallow Ocean of Air Russian Space Station Mir http://solarsystem.nasa.gov The shallow depth of the Earth’s atmosphere can be seen along the horizon.

16. Chemical Cycle in Ecosystems Sunlight http://img.dailymail.co.uk Photosynthesis Chloroplasts in plants http://pws.byu.edu C6H12O6 (glucose) + O2(oxygen) CO2 (carbon dioxide) + H2O (water) Cellular Respiration Mitochondria in animals and plants http://www.soquel.org ATP Cellular Work

17. Where We Are Headed http://therreddragonm.com The rest of this lecture is about the production of chemical energy in consumers. Next week we will discuss producers and photosynthesis. http://www,kipapanursery.com

18. Cellular Respiration • Cellular respiration is a form of metabolism, the term for the sum of all chemical processes that occurs in cells. • A large part of cellular respiration occurs in the mitochondria. • The potential energy in food is converted to chemical energy that can be used by cells. • Over two dozen chemical reactions are involved in cellular respiration. • A specific enzyme catalyzes each reaction in the metabolic pathways.

19. High-Level View • We will examine cellular respiration at a fairly high level—some of the illustrations were chosen to convey the complexity of the biochemical processes. • I will point out the illustrations that you don’t need to know in detail for this course.

20. Potential Energy of Food http://oregon.4h.oregonstate.edu Food is a form of potential energy that can be converted to chemical energy.

21. Adenosine Triphosphate • As we discussed last week, ATP has a tail consisting of three phosphate groups. • Chemical energy is released when a phosphate group is split from the tail forming ADP.

22. ATP Molecule http://biology.clc.uc.edu Tail containing three phosphate groups

23. Release of Chemical Energy • Some of the energy is used to recycle ATP by adding a phosphate group to ADP. • The splitting-off of a phosphate group from ATP also contributes electrons to NAD+ to form NADH. • NADH provides additional energy for performing cellular work through the electron transport chain. • Energy release is used by the cell’s organelles to perform their functions.

24. Basic Chemical Equation • The basic chemical equation for cellular respiration is shown on the next slide. • The left- and right-hand sides of the equation were seen in the ‘Chemical Cycling in Ecosystems’ slide of the interrelationship between producers and consumers. • The overall chemical reaction is a form of redox reaction, which we won’t discuss—you can read more about it in your textbook if you are interested.

25. The Equation + + + C6H12O6 (glucose) 6O2 6CO2 6H20 ATP (chemical energy) Cellular Respiration ATP molecule Glucose molecule http://biology.clc.uc.edu http://eurekalert.org

26. Chemical Cycle in Ecosystems, Redux Sunlight http://img.dailymail.co.uk Photosynthesis Chloroplasts in plants http://pws.byu.edu C6H12O6 (glucose) + O2(oxygen) CO2 (carbon dioxide) + H2O (water) Cellular Respiration Mitochondria in animals and plants http://www.soquel.org ATP Cellular Work

27. Cellular Respiration 1. Glycolysis A human lymphocyte cell and the visible organelles including a number of mitochondria. 2. Krebs Cycle 3. Electron Transport Chain The three processes involved in cellular respiration http://www.sinauer.com

28. Glycolysis • Glycolysis takes place in the cytoplasm of eukaryotic and prokaryotic cells. • The process is anaerobic, that is, it does not use oxygen. • Glycolysis breaks six-carbon glucose molecules into two, three-carbon molecules of pyruvic acid. • Two molecules of ATP are produced—pyruvic acid also donates two high-energy electrons to the molecule NAD+ for the electron transport chain. • NAD+ is converted to NADH once the high-energy electron is donated. • Pyruvic acid contains most of the chemical energy of glucose, which is harvested in the Krebs cycle.

29. Biochemistry of Glycolysis http://staff.jccc.net

30. Krebs Cycle • The Krebs cycle takes place in mitochondria of plant and animal eukary-otic cells. • The process is also known by other names including the citric acid cycle.

31. Chemical Reactions • Pyruvic acid is first converted to acetic acid before attaching to the carrier molecule, coenzyme A, for entry into the Krebs cycle. • The Krebs cycle extracts chemical energy until CO2is formed, a major by-product of cellular respiration. • The cycle produces two molecules of ATP, and donates six high-energy electrons to NAD+ for the electron transport chain. • The cycle also donates two high-energy electrons to another molecule, FADH2 for the electron transport chain.

32. Biochemistry of the Krebs Cycle http://upload.wikimedia.org

33. Electron Transport Chain • The molecules of the electron transport chain are in the inner membrane of the mitochondria. • Hydrogen ions (H+) ‘fall’ toward oxygen molecules that entered the mito-chondria through diffusion along their concentration gradient. • The electron transport chain uses the high-energy electrons in NADH to pump hydrogen ions (H+) against their concentration gradient across the membrane of the mitochondria.

34. Electron Transport Chain, Continued • The hydrogen ions diffuse along their concentration gradient (from high to low concentration) back into the mitochondria. • The H+ inflow turns tiny ‘turbines’ made of protein molecules located in the membrane.

35. Analogy Boulder Dam, Nevada and Arizona http://www.mcnarybergeron.com Turbines connected to generators produce electrical energy from the downhill flow of water. Powerhouse turbines http://www.bossanova.com

36. ATP Synthase • Energy from each turbine, known as ATP synthase, is used in attaching a phosphate group to an ADP molecule to regenerate an ATP molecule. • Up to 34 ATP molecules are produced by the ATP synthase—compare with the much smaller ATP output from glycolysis and the Krebs cycle. http://www.sparknotes.com

37. When Things Go Wrong http://safety.more4kids.com • Carbon monoxide (CO) and cyanide block the transfer of the high-energy electrons to oxygen in the electron transport chain. • The mitochondria can no longer harvest food energy to convert ADP to ATP. • The cells stop working and the organism can die, often very rapidly.

38. Versatility of Cellular Respiration • We have focused on glucose as a fuel source for cellular respiration. • Cellular respiration also uses other carbohydrates, fats, and proteins. • The digestive process hydrolyzes large food molecules into monomers that can be used by glycolysis and the Krebs cycle. http://www.borderfoodsinc.com

39. Anaerobic Effort • Cells can work for short periods of time without oxygen through the anaerobic conversion of glucose to chemical energy. • Anaerobic, a type of fermentation, means ‘without oxygen.’ • Muscles cells have an adequate number of ATP molecules to support anaerobic activity for about five seconds. • They have a secondary supply of the molecule creatine phosphate to provide an additional ten seconds of energy reserve. http://blog.beyou.tv

40. Glycolysis and Anaerobic Effort • Glycolysis is the anaerobic pathway that can provide a limited number of ATP molecules for cellular work in the absence of oxygen. • The process isn’t efficient since two ATP molecules are produced for every glucose molecule compared to 36 ATP molecules in the Krebs cycle and electron transport chain. • To provide energy for a final dash to the finish line, cells compensate by consuming more glucose molecules per second, provided the body has an adequate supply of carbohydrates.

41. Lactic Acid • Pyruvic acid is the by-product of glycolysis, which is converted (meta-bolized) to lactic acid. • When exercising vigorously, lactic acid accumulates in muscles, often leading to a burning sensation and soreness. • The muscles may temporarily shut down (‘hitting the wall’) if lactic acid accumulates in high concentrations. • The lactic acid is eventually transported to the liver and converted to pyruvic acid. • This process requires oxygen, and this is why we may breathe so hard even after we stop exercising.

42. Fermentation in Foods • Some fungi and bacteria produce lactic acid as a by-product of fermen-tation. • Microbes have been domesticated to transform milk into cheese, sour cream, and yogurt—the sharp flavor of some of these products is due to lactic acid. • Fermentation is used in producing soy sauce, pickles, olives, pepperoni, and salami, among other foods. http://www.sks-bottle.com http://www.talamospizza1.com

43. Yeast • Yeast is a fungus capable of both cellular respiration and fermentation. • If kept without oxygen, yeast produces sugars and the by-products, CO2 and ethyl alcohol. • The carbon dioxide bubbles produced by yeast enable bread dough to rise. • Ethyl alcohol is a major component and active ingredient of alcoholic beverages.

44. Budding Yeast Electron micrograph of budding yeast http://upload.wikimedia.org Yeast in the process of reproducing.

45. Bread http://biology.clc.uc.edu Bread, with pockets resulting from CO2 bubbles during fermentation.

46. Alcoholic Beverages http://www.auark.edu Wine grapes covered in a yeast growth known as ‘blush.’

47. Wine Production http://www.answers.com The fermentation process in the 16th century—the basic principles remain the same.

48. Anaerobes • Yeast are known as facultative anaerobes since they can harvest food energy through either cellular respiration or fermentation. • Obligate anaerobes, such as some bacteria living in stagnant ponds or in the soil, are poisoned by oxygen. Clostridium difficile, an obligate anaerobe http://www.theguardians.com

49. http://www.zo.utexas.edu Volcanoes released many gases containing molecules necessary for the formation of early life—they include methane, carbon dioxide, water, and ammonia. A Much Younger Earth

50. Earliest Life • The Krebs cycle and electron transport chain operate only in aerobic conditions (when O2 is present). • Glycolysis can operate under anaerobic and aerobic conditions since it is not dependent upon oxygen. • Bacteria first formed about 3.5 billion years ago, and used glycolysis to produce ATP. • Oxygen, a by-product of certain photosynthetic bacteria, did not begin accumulating in the atmosphere until about 2.5 billion years ago. • The accumulation paved the way for the use of O2 by eukaryotic cells.