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  1. 1. Cellular RespirationReleasing Chemical Energy Chapter 6
  2. 2. BIOCHEMICAL REACTIONS• All living organisms require a constant supply of energy to sustain life.• Cellular respiration - the chemical energy stored in glucose is converted into a more usable form – ATP – Requires the presence of oxygen and the correct enzymes – Carbon dioxide, water and heat are also released as by-products of this reaction.C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat)glucose + oxygen → carbon + water + energy dioxide
  3. 3. Why Cell “Respiration”?2. This process requires oxygen, which is supplied by breathing3. The mechanical movement of air or water through the lungs/gills is often referred to as ventilation to distinguish it from respiration.4. What about plants?
  4. 4. • Cellular respiration – slow, controlled release of energy (max. harvest of energy from food)
  5. 5. Review of ATP
  6. 6. Review of ATP• ATP is the “energy currency/rechargeable batteries” of cells• When energy is harvested from a chemical reaction or sunlight, it is stored when a phosphate group is attached to an ADP to form ATP. – Called phosphorylation
  7. 7. • When the ATP is broken back down to ADP, stored chemical energy is released to do work in a cell – Called dephosphorylation – Some energy is lost as heat
  8. 8. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat)glucose + oxygen → carbon + water + energy dioxide
  9. 9. OXIDATION REACTIONS• Oxidation begins in the cytoplasm and is completed in the mitochondria• 3 parts to cellular respiration (each an enzyme-controlled pathway) – Glycolysis – Krebs cycle – Electron transport system
  10. 10. Overview
  11. 11. • Animation: es/Faculty/DMeyer/respiration.html
  12. 12. 1. Glycolysis - a 6C glucose molecule is broken into 2 3C molecules of pyruvate (pyruvic acid) a. Occurs in the cytoplasm of the cell – near the mitochondria b. Yields: + 2 ATP (4 ATP – 2ATP - used to phosphorylate glucose when it enters cell) + 2 NADH (NAD+ is reduced to NADH) c. This process is anaerobic (without oxygen)…can happen even if there is an insufficient O2 level to carry out the rest of cellular respiration
  13. 13. If there is O2 present, respiration continues. Each 3C pyruvate will…2. Lose atoms of carbon and oxygen – CO2 released (…it is now called an acetyl group)4. Join to a molecule of coenzyme A (which is a B vitamin) – Acetyl CoA - CoA acts as a shuttle, carrying acetyl groups3. NAD+ (coenzyme that shuttles around hydrogen and electrons) is reduced to NADH.4. These reactions are often called the ‘Intermediate Reactions’
  14. 14. 2. Kreb’s Cycle (Citric Acid Cycle) a. Acetyl CoA enters the mitochondrion and 2C acetyl group bonds to a 4C compound (oxaloacetate) to form a 6C compound called Citric Acid (citrate)
  15. 15. b. The 6C compound is broken down to a 5C compound 1 CO2 is produced 1 NAD+ is reduced to NADH
  16. 16. c. 5C compound is broken down into a 4C compound 1 CO2 is produced 1 NAD+ is reduced to NADHd. Oxaloacetate is regenerated (4C  4C)This yields: 1 ATP (ADP  ATP) 1 FADH2 (FAD  FADH2) 1 NADH (NAD+  NADH)
  17. 17. e. So, the total yield of just the Kreb’s cycle is: 2 ATP 6 NADH 2 FADH2 per glucose
  18. 18. 3. Electron transport system (ETS) makes ATP a. Electrons from reduced coenzymes NADH and FADH2 are transferred through a series of redox reactions until the electrons are accepted by oxygen to make water.
  19. 19. b. Mitochondrial structure 1) Double membrane- bound organelle 2) Inner membrane folded into christae a) Increase surface area for reactions b) ETS located here • Intermembrane space • Matrix - Kreb’s cycle
  20. 20. c. ATP synthesis 1. H atoms from coenzymes dropped off at ETS (inner membrane) 2. H atoms split into a proton (H+) and an electron (e-) - Electrons go through ETS - Energy from electrons is used to pump the H+ out into the intermembrane space 3. H+ concentration in this space increases 4. The H+ RUSH back into the matrix (because of concentration gradient) through an H+ channel (ATP synthetase complex) making ATP 5. Called chemiosmosis
  21. 21. • Animation: adient/movie.htm
  22. 22. d. Happy endings… 1. H+ and e- (now low energy) are rejoined 2. H atoms bond to available oxygen atoms and form water: H+ + e - + O2  H2O This is why you breathe!! The O2 is merely a hydrogen dump! O2 allows the continual movement of H+ through the ATP synthetase No O2, no rushing H+ movement, no ATP, no life!
  23. 23. e. ETS produces: (per glucose) 2 NADH (from glycolysis) 2 NADH (from intermediate reactions) + 6 NADH (Krebs cycle)______________ 10 NADH x 3 ATP/NADH = 30 ATP 2 FADH2 x 2 ATP/ FADH2 = 4 ATP____ for a total 34 ATP/glucose from ETS
  24. 24. Cellular Respiration Energy Summary34 ATP/glucose from ETS +2 ATP (glycolysis) +2 ATP (Krebs cycle)_______________ 38 ATP per glucose!!!
  25. 25. • Prisoners’ explanation
  26. 26. • Current applications
  27. 27. • Other nutrients can be used for energy – Lipids fatty acids, enter Krebs Cycle – Proteins amino acids • NH3 removed urea • Carbon portions enter Krebs Cycle as oxaloacetate – Carbon skeletons can be used for biosynthesis of amino acids, nucleic acids and fatty acids
  28. 28. Alternatives to Aerobic RespirationWhat if there’s not enough oxygen?
  29. 29. Glycolysis still happens (since it’s anaerobic anyway…). - Yield is 2 ATP + 2 NADH + 2 pyruvic acid (3 C molecule). - Fate of the pyruvic acid depends on what type of organism you are…
  30. 30. If you are a plant or yeast cell…Pyruvic acid will become ETHANOL in a process called alcoholic fermentation.
  31. 31. If you are a bacterial cell… Your pyruvic acid can be fermented to vinegar or to start the process of cheesemaking.
  32. 32. If you are an animal cell…Your pyruvic acid becomes LACTIC ACID in a process called lactic acid fermentation.
  33. 33. Photosynthesis and Cellular Respiration• Cellular respiration and photosynthesis share several features: – They are enzyme-controlled biochemical pathways. – They make use of ATP for energy transfer – They use an Electron Transport System to help make ATP.
  34. 34. Photosynthesis and Cellular Respiration
  35. 35. Photosynthesis and Cellular RespirationLight + 6 CO2 + 6 H2O → C6H12O6 + 6 O2C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat)
  36. 36. • End of cellular respiration!
  37. 37. Acetyl CoA NADH FADH NADPH
  38. 38. CELLULAR RESPIRATION• Breakdown of glucose molecules in the presence of oxygen.• The oxidation of glucose (by many enzymes) results in carbon dioxide and water.C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat) glucose + oxygen → carbon + water + energy dioxide
  39. 39. A Definition of Cellular RespirationThe energy stored in glucose (with the presence of oxygen and the correct enzymes) is converted into a more usable form – ATP. Carbon dioxide and water are also released as by-products of this reaction.C6H12O6 + 6 O2  6 CO2 + 6 H2O + ATP[Read the last paragraph on page 131]
  40. 40. GLYCOLYSIS• Glucose (6 carbons) is broken into two 3 carbon molecules called pyruvate (pyruvic acid).• This makes enough energy to make 2 ATP molecules.• In addition, an NADH molecule is also made and transferred to the electron transport chain.
  41. 41. 3. Electron transport system (ETS), located in the membranes of mitochondria (and chloroplasts) makes ATP. – High-energy electrons are passed stepwise through a series of oxidation- reduction reactions from one carrier molecule to another. • Every time the electron is passed, some of its energy is released and can be used to make ATP • The rest of the energy is released as heat
  42. 42. How much energy do you get from 1 molecule of glucose?Glycolysis – 2ATP and 2 NADH (each x3)Intermediate – 2 NADH (each x3)Kreb’s Cycle – 2 ATP, 6 NADH (each x3), and 2 FADH2 (each x2)The ETS yields 8 ATP from glycolysis, 6 ATP from the Intermediate Reactions, 24 ATP from the Kreb’s CycleFor a total of…38 ATP per initial molecule of glucose
  43. 43. Throughout the process, coenzymesare being reduced so, in the end, they can all be oxidized (so ATP can be generated!) – sort of like POKER!
  44. 44. CELLULAR RESPIRATION SUMMARY• Glucose is broken down to carbon dioxide and water, making 4 ATPs directly and another 32 ATP via the electron transport system.