Chapter 7 - Cellular Respiration

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  • Photo Credits: left: ©Bob Gurr/DRK Photo; middle bottom: ©John Durham/Science Photo Library/Photo Researchers, Inc. ; middle top: ©Ron Boardman/Stone; right: ©Keith Porter/Photo Researchers, Inc.
  • Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen. Glycolysis takes place in the cytoplasm. The Krebs cycle and electron transport take place inside the mitochondria.
  • Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen. Glycolysis takes place in the cytoplasm. The Krebs cycle and electron transport take place inside the mitochondria.
  • Glycolysis is the first stage in cellular respiration . During glycolysis, glucose is broken down into 2 molecules of pyruvic acid.
  • Lactic acid fermentation converts glucose into lactic acid. The first part of the equation is glycolysis. The second part shows the conversion of pyruvic acid to lactic acid.
  • Lactic acid fermentation converts glucose into lactic acid. The first part of the equation is glycolysis. The second part shows the conversion of pyruvic acid to lactic acid.
  • Photo Credits: left: ©Bob Gurr/DRK Photo; middle bottom: ©John Durham/Science Photo Library/Photo Researchers, Inc. ; middle top: ©Ron Boardman/Stone; right: ©Keith Porter/Photo Researchers, Inc.
  • The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.
  • The electron transport chain uses high-energy electrons from the Krebs cycle to convert ADP to ATP.
  • The electron transport chain uses high-energy electrons from the Krebs cycle to convert ADP to ATP.
  • The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.
  • Chapter 7 - Cellular Respiration

    1. 1. •Food serves as a source of raw materials for the cells in the body and as a source of energy. •Cells break down food into simpler molecules in a process that releases energy to power cellular activities. Animal CellsAnimal Mitochondrion Plant Plant Cells
    2. 2. Harvesting Chemical Energy• Cellular respiration is the process by which cells break down organic compounds (food) to produce ATP.• Both autotrophs and heterotrophs perform cellular respiration.• The primary fuel for cellular respiration is glucose, which is formed when carbohydrates such as starch and sucrose are broken down.• If too few carbohydrates are available, other molecules, such as fats and proteins can be broken down to make ATP.
    3. 3. Harvesting Chemical Energy• When cells break down food molecules, some of the energy in the molecules is released as heat.• The remaining energy is stored in molecules of ATP.• ATP is the energy “currency” of cells.
    4. 4. Adenosine Triphosphate• ATP supplies energy for 3 main types of biological work: – Mechanical functions of cells – Active transport of ions and molecules across cell membranes – Synthesis and breakdown of large molecules• The phosphate groups of ATP store energy.• This energy is released when the bonds that hold the phosphate groups together are broken.• The cell uses this energy to do work.
    5. 5. The ATP-ADP Cycle
    6. 6. Overview of Cellular Respiration Electrons carried in NADH Electrons carried in NADH and Pyruvic FADH2 acidGlucose Glycolysis Cytoplasm Mitochondrion
    7. 7. Overview of Cellular Respiration• Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.• The equation for cellular respiration is: 6O2 + C6H12O6 → 6CO2 + 6H2O + Energy oxygen + glucose → carbon dioxide + water + Energy
    8. 8. Overview of Cellular Respiration• Glycolysis takes place in the cytoplasm. The Krebs cycle and electron transport take place in the mitochondria. GlycolysisCytoplasm Mitochondrion
    9. 9. Glycolysis• ATP Production − At the beginning of glycolysis, the cell uses up 2 molecules of ATP to start the reaction. 2 ATP 2 ADP 4 ADP 4 ATPGlucose 2 Pyruvic acid
    10. 10. Glycolysis− When glycolysis is complete, 4 ATP molecules have been produced. 2 ATP 2 ADP 4 ADP 4 ATPGlucose 2 Pyruvic acid
    11. 11. Glycolysis− This gives the cell a net gain of 2 ATP molecules. 2 ATP 2 ADP 4 ADP 4 ATPGlucose 2 Pyruvic acid
    12. 12. Glycolysis• NADH Production − One reaction of glycolysis removes 4 high- energy electrons, passing them to an electron carrier called NAD+. 2 ATP 2 ADP 4 ADP 4 ATP Glucose 2NAD+ 2 Pyruvic acid
    13. 13. Glycolysis− Each NAD+ accepts a pair of high-energy electrons and becomes an NADH molecule. 2 ATP 2 ADP 4 ADP 4 ATPGlucose 2NAD+ 2 Pyruvic 2 acid
    14. 14. Glycolysis− The NADH molecule holds the electrons until they can be transferred to other molecules. 2 ATP 2 ADP 4 ADP 4 ATP 2NAD+ 2 Pyruvic 2 acid To the electron transport chain
    15. 15. Glycolysis• The Advantages of Glycolysis − The process of glycolysis is so fast that cells can produce thousands of ATP molecules in a few milliseconds. − Glycolysis does not require oxygen.
    16. 16. Fermentation• When oxygen is not present, glycolysis is followed by a different pathway. The combined process of this pathway and glycolysis is called fermentation.• Fermentation does not require oxygen—it is an anaerobic process.• Fermentation does not produce ATP, but it does regenerate NAD+, which allows for the continued production of ATP through glycolysis.
    17. 17. Fermentation• There are many types of fermentation. Two of the most common types are: – Alcoholic fermentation – Lactic acid fermentation
    18. 18. • Alcoholic Fermentation − When oxygen is not present, yeasts and certain bacteria use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes. − The equation for alcoholic fermentation after glycolysis is: pyruvic acid + NADH → alcohol + CO2 + NAD+ − Yeasts, added to crushed grapes, eat the grapes’ sugars and produce wine when there is no oxygen present. − Yeasts, added to the grain barley, eat the grain’s sugars and produce beer when there is no oxygen present.
    19. 19. • http://www.youtube.com/watch? v=mqioniPbEHQ• http://www.youtube.com/watch? v=JfsQEVDxuFI
    20. 20. • Alcoholic Fermentation − The CO2 released by the yeast causes the carbonation of some alcoholic beverages, such as champagne and beer. − Yeasts, added to dough, digest sugars (derived from starches in dough) and produce carbon dioxide, causing the dough to rise.
    21. 21. • Lactic Acid Fermentation − In some cells, pyruvic acid that accumulates as a result of glycolysis can be converted to lactic acid when oxygen is not present. − This type of fermentation is called lactic acid fermentation. Like alcoholic fermentation, it regenerates NAD+ so that glycolysis can continue. − The equation for lactic acid fermentation after glycolysis is: pyruvic acid + NADH → lactic acid + NAD+
    22. 22. • Lactic Acid Fermentation – During strenuous exercise, oxygen is scarce; therefore, human muscle cells switch from aerobic respiration to lactic acid fermentation.  Lactic acid that accumulates as a waste product may cause muscle soreness, but it is gradually carried away by the blood to the liver.  Lactic acid is converted back to pyruvic acid by liver cells.
    23. 23. • Lactic Acid Fermentation − Lactic acid fermentation by certain fungi and bacteria is used in the dairy industry to make cheese and yogurt.  Milk bacteria digest the milk sugar lactose and produce lactic acid, which acts with the added enzyme rennet to curdle the milk. The cheesemaker drains off the whey and compacts the curds, which various microbes then ripen into a mature cheese. − Lactic acid fermentation is also used to make pickles and sauerkraut.  The cucumbers and cabbage are soaked in a salt brine and sealed, allowing the growth of bacteria that eat the vegetable’s sugars and produce tart-tasting lactic acid.
    24. 24. • http://www.youtube.com/watch? v=d0UfS1bqscM
    25. 25. • The first part of the equation is glycolysis.
    26. 26. • The second part shows the conversion of pyruvic acid to lactic acid.
    27. 27. Efficiency of Glycolysis• After glycolysis, only about 2% of the energy contained in glucose has been transferred to ATP.• Most of the energy is still stored in pyruvic acid.• Large organisms that require more energy will meet their needs by undergoing aerobic respiration.
    28. 28. Overview of Aerobic Respiration • After glycolysis, if oxygen is present, fermentation will not occur. Instead, 2 pathways called the Krebs cycle and the Electron Transport Chain will occur. • Because these pathways of cellular respiration require oxygen, they are aerobic. • Aerobic respiration produces nearly 20 times as much ATP as is produced by glycolysis alone.
    29. 29. • Both plant and animal cells carry out the Krebs cycle and the Electron Transport Chain in the mitochondria.Animal Cells Outer membrane Intermembrane Mitochondrion space Inner membrane Matrix Plant Cells
    30. 30. Overview of Aerobic Respiration
    31. 31. The Krebs Cycle • Discovered by Hans Krebs in 1937 • He received the Nobel Prize in physiology or medicine in 1953 for his discovery. • Forced to leave Germany prior to WWII because he was Jewish • The Krebs cycle occurs in the mitochondrial matrix. Mitochondrial Matrix
    32. 32. The Krebs Cycle• During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.
    33. 33. – The Krebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion.
    34. 34. – One carbon atom is removed, forming CO2, and electrons are removed, changing NAD+ to NADH.
    35. 35. – Coenzyme A joins the 2-carbon molecule, forming acetyl-CoA.
    36. 36. – Acetyl-CoA then adds the 2-carbon acetyl group to a 4- carbon compound, forming citric acid, a 6-carbon compound. Citric acid
    37. 37. – Citric acid is broken down into a 5-carbon compound, then into a 4-carbon compound.
    38. 38. – Two more molecules of CO2 are released and electrons join NAD+ and FAD, forming NADH and FADH2. NADH and FADH2 carry high-energy electrons and are referred to as “Electron Taxis”.
    39. 39. – In addition, one molecule of ATP is generated.– However, the Krebs cycle turns twice (once for each pyruvic acid molecule produced in glycolysis)!
    40. 40. The Krebs Cycle• Totals after the Krebs Cycle: – 2 ATP – 8 NADH (plus 2 NADH from glycolysis = 10 total NADH) – 2 FADH2 – 6 CO2• Most of the energy released in the breakdown of glucose still has not been transferred to ATP.• The 10 NADH molecules and the 2 FADH2 molecules drive the next stage of aerobic respiration where most of the energy transfer occurs.
    41. 41. Electron Transport Chain• The electron transport chain (or ETC) uses the high-energy electrons from NADH and FADH2 to convert ADP into ATP by moving protons down their concentration gradient (chemiosmosis).– The ETC is located in the inner mitochondrial membrane in folds called cristae. Inner Mitochondrial Membrane
    42. 42. – High-energy electrons from NADH and FADH2 are passed along the electron transport chain from one carrier protein to the next.
    43. 43. – At the end of the chain, an enzyme combines these electrons with hydrogen ions and oxygen to form water.
    44. 44. – As the final electron acceptor of the electron transport chain, oxygen gets rid of the low-energy electrons and hydrogen ions.  The Importance of Oxygen  ATP can only be produced if electrons keep moving down the electron transport chain  Without oxygen to accept electrons, the electron transport chain stops and no more ATP can be produced
    45. 45. – When 2 high-energy electrons move down the electron transport chain, their energy is used to move hydrogen ions (H+) across the membrane.
    46. 46. – During electron transport, H+ ions build up in the intermembrane space, so it is positively charged.
    47. 47. – The other side of the membrane, from which those H+ ions are taken, is now negatively charged.
    48. 48. – The inner membranes of the mitochondria contain proteins called ATP synthases. ATP synthase
    49. 49. – H+ ions move down their concentration gradient through channels into the ATP synthase. This causes the ATP synthase to spin. Channel ATP synthase
    50. 50. – As it rotates, the enzyme grabs a low-energy ADP, attaching a phosphate, forming high-energy ATP. Channel ATP synthase ADP
    51. 51. Electron Transport Chain Animation
    52. 52. Electron Transport Chain Song
    53. 53. The Totals• Glycolysis produces just 2 ATP molecules per molecule of glucose.• The complete breakdown of glucose through aerobic cellular respiration, including glycolysis, results in the production of 36 molecules of ATP. − Efficiency of Cellular Respiration  This represents about 37% of the energy stored in glucose.  The remaining energy is released as heat.
    54. 54. The Totals
    55. 55. Comparing Aerobic & Anaerobic Cellular Respiration Pathways Aerobic Anaerobic (needs (no oxygen) oxygen)Occurs in: Most Mostly yeast organisms and bacteria1 glucose 6 CO2 + 6 H2O Ethanol + CO2makes: or lactic acidNet ATP 36 2production:
    56. 56. Comparing Photosynthesis and Cellular Respiration• The energy flows in photosynthesis and cellular respiration take place in opposite directions.
    57. 57. Photosynthesis-Cellular Respiration Cycle
    58. 58. Comparing Photosynthesis and Cellular Respiration• On a global level, photosynthesis and cellular respiration are also opposites. – Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back. – Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.

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