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Respiration

Respiration. Cellular respiration is the process by which cells transfer chemical energy from sugar molecules to ATP molecules. As this happens cells release CO 2 and use up O 2 Respiration can be AEROBIC or ANAEROBIC. O 2. Breathing. CO 2. Lungs. O 2. CO 2. Bloodstream.

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Respiration

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  1. Respiration • Cellular respiration is the process by which cells transfer chemical energy from sugar molecules to ATP molecules. • As this happens cells release CO2 and use up O2 • Respiration can be AEROBIC or ANAEROBIC

  2. O2 Breathing CO2 Lungs O2 CO2 Bloodstream Muscle cells carrying out Cellular Respiration Glucose + O2 CO2 +H2O +ATP 0 Breathing supplies oxygen to our cells and removes carbon dioxide • Breathing provides for the exchange of O2 and CO2 Between an organism and its environment Figure 6.2

  3. 0 . The human body uses energy from ATP for all its activities. • ATP powers almost all cellular and body activities

  4. CELLULAR RESPIRATION • Cellular respiration is an energy- releasing process. It produces ATP • ATP is the universal energy source Making ATP • Plants make ATP during photosynthesis • Cells of all organisms make ATP by breaking down carbohydrates, fats, and protein

  5. Phosphategroups Adenosine diphosphate Adenosine Triphosphate H2O + P Energy P P P P P + Hydrolysis Adenine Ribose ATP ADP • The energy in an ATP molecule • Lies in the bonds between its phosphate groups Figure 5.4A

  6. REDOX REACTIONS • The loss of electrons is called oxidation. • The addition of electrons is called reduction

  7. Overview of Aerobic Respiration C6H12O6 + 6O2 6CO2 + 6H2O +ATP glucose oxygen carbon water dioxide

  8. Loss of hydrogen atoms (oxidation) C6H12O6 6 CO2 Energy 6 O2 + 6 H2O + + Glucose (ATP) Gain of hydrogen atoms (reduction) 0 • When glucose is converted to carbon dioxide • It loses hydrogen atoms, which are added to oxygen, producing water Figure 6.5A

  9. 0 STAGES OF CELLULAR RESPIRATION Overview: Cellular respiration occurs in three main stages • Glycolysis • Krebs Cycle or Citric Acid Cycle • Electron Transport Chain or Phosphorylation

  10. 0 • Stage 1: Glycolysis • No oxygen needed. It is universal • Occurs in the cytoplasm • Breaks down glucose into pyruvate, producing a small amount of ATP (2)

  11. GLYCOLYSIS • Where?: In the cytosol of all cells. Both aerobic and anaerobic respiration begin with glycolysis. • What happens?: The cell harvests energy by oxidizing glucose to pyruvate. • One molecule of glucose (6 carbons) is converted to two pyruvate molecules (3 carbons) through a series of 10 reactions mediated by enzymes. • Result: 2 pyruvate molecules (each with a 3 carbon backbone) 2 NADH molecules. Carrier that picks up hydrogens stripped from glucose. 2 ATP molecules. 4 are made but cells use 2 to start glycolysis so net gain is 2

  12. An overview of cellular respiration

  13. Preparatory steps to enter the Krebs cycle • The 2 pyruvate molecules enter the mitochondrion and an enzyme strips one carbon from each pyruvate. • This two carbon molecule is picked up by Co-enzyme A in preparation for the Krebs cycle. • This is acetyl CoA. This is what enters the Krebs cycle: C-C-CoA (oxaloacetate)

  14. 0 Stage 2 : The citric acid cycle or Krebs cycle • Takes place in the mitochondria • Completes the breakdown of glucose (catabolism), producing a small amount of ATP (2ATP) • Pyruvate is broken down to carbon dioxide • More coenzymes are reduced .Supplies the third stage of cellular respiration with electrons (hydrogen carriers such as NADH)

  15. KREBS CYCLE or citric acid cycle • This cycle involves a series of 8 steps forming and rearranging. Each time it releases CO2 and NADH carries hydrogen to the last step. 6 CO2are given off as waste (this is the most oxidized form of Carbon)In total: 6 CO2 6 NADH are produced and 2 FADH and only 2 ATP

  16. An overview of cellular respiration

  17. 0 Stage 3: Oxidative phosphorylation or electron transport chain • Occurs in the mitochondria (inner membrane) • Uses the energy released by “falling” electrons to pump H+ across a membrane • Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP

  18. Chemiosmosis Chemiosmosis is an energy coupling mechanism that uses energy stored on H+ Chemiosmosis is the coupling of the REDUX reactions of the electron transport chain to ATP synthesis

  19. NADH ATP NAD+ + 2e Controlled release of energy for synthesis of ATP H+ Electron transport chain 2e 1 O2 2 H+ 2 H2O 0 • NADH passes electrons to an electron transport chain • As electrons “fall” from carrier to carrier and finally toO2 • Energy is released in small quantities Figure 6.5C

  20. ELECTRON TRANSPORT CHAIN • Electron transport systems are embedded (proteinmolecules) in inner mitochondrial membranes (cristae) • NADH and FADH2 give up electrons that they picked up in earlier stages to electron transport system • Electrons are transported through the system • The final electron acceptor is oxygen. The hydrogen combines with the oxygen to form water

  21. . H+ H+ H+ H+ H+ Protein complex H+ H+ ATP synthase H+ Electron carrier H+ Intermembrane space Inner mitochondrial membrane FADH2 FAD Electron flow 1 +2 O2 H+ NAD+ NADH 2 H+ H+ Mitochondrial matrix + P ATP ADP H+ H2O H+ Chemiosmosis Electron Transport Chain OXIDATIVE PHOSPHORYLATION Figure 6.10 Electron transport chain

  22. HOW MUCH TOTAL ATP(ENERGY) WAS PRODUCED? • Glycolysis 2 ATP formed by substrate-level phosphorylation • Krebs cycle and preparatory reactions 2 ATP formed by substrate-level phosphorylation • Electron transport phosphorylation 32-34 ATP formed 2+2+34=38 Most ATP production occurs by oxidative phosphorylation or electron transport chain

  23. WHY OXYGEN? • Electron transport phosphorylation requires the presence of oxygen • Oxygen withdraws spent electrons from the electron transport system, then combines with H+ to form water

  24. Web site tutorials to check: • http://www.sp.uconn.edu/~terry/Common/respiration.html • http://www2.nl.edu/jste/electron_transport_system.htm • http://www.wisc-online.com/objects/MBY2604/MBY2604.swf

  25. An overview of cellular respiration

  26. An overview of cellular respiration

  27. Animation: Cell Respiration Overview

  28. How efficient is cellular respiration? • Only about 40% efficient. In other words, a call can harvest about 40% of the energy stored in glucose. • Most energy is released as heat

  29. Evolution of cellular respiration • When life originated, atmosphere had little oxygen • Earliest organisms used anaerobic pathways • Later, photosynthesis increased atmospheric oxygen • Cells arose that used oxygen as final acceptor in electron transport (without oxygen to act as the final hydrogen acceptor the cells will die)

  30. Fermentation • Fermentation allows some cells to produce ATP without oxygen. • This is Anaerobic respiration

  31. ANAEROBIC RESPIRATIONFermentation is an anaerobic alternative to cellular respiration • Do not use oxygen • Produce less ATP( 2) than aerobic pathways • Two types. One produces alcohol and the other lactic acid as waste products • Fermentation pathways • Anaerobic electron transport

  32. Fermentation • Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP • Begin with glycolysis • Do not break glucose down completely to carbon dioxide and water • Yield only the 2 ATP from glycolysis • Steps that follow glycolysis serve only to regenerate NAD+

  33. Yeast • Single-celled fungi • Carry out alcoholic fermentation • Saccharomyces cerevisiae • Baker’s yeast • Carbon dioxide makes bread dough rise • Saccharomyces ellipsoideus • Used to make beer and wine

  34. Our muscle cells… • In the absence of oxygen our muscles can carry out fermentation, but the pyruvate from glycolysis is turned into lactic acid instead of alcohol

  35. NADH NAD+ 2 NAD+ NADH 2 2 2 GLYCOLYSIS 2 ADP + 2 CO2 released 2 P 2 ATP 2 Ethanol Glucose 2 Pyruvate Figure 6.13B 0 • In alcohol fermentation • NADH is oxidized to NAD+ while converting pyruvate to CO2 and ethanol Figure 6.13C

  36. More details…

  37. Two stages of glycolysis • Energy-requiring steps • ATP energy activates glucose and its six-carbon derivatives • Energy-releasing steps • The products of the first part are split into three-carbon pyruvate molecules • ATP and NADH form

  38. H+ 2 + 2 NAD+ 2 NADH Glucose 2 Pyruvate + 2 2 P ATP 2 ADP 0 • Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • In glycolysis, ATP is used to prime a glucose molecule • Which is split into two molecules of pyruvate Figure 6.7A

  39. 4 3 1 • In the first phase of glycolysis • ATP is used to energize a glucose molecule, which is then split in two PREPARATORY PHASE(energy investment)  Steps      –   A fuel molecule is energized, using ATP. Glucose ATP Step 1 ADP Glucose-6-phosphate P 2 P Fructose-6-phosphate ATP 3 ADP P Fructose-1,6-diphosphate P  Step      A six-carbon intermediate splits into two three-carbon intermediates. 4 Figure 6.7C

  40. 5 5 6 6 7 7 8 8 9 9 • In the second phase of glycolysis • ATP, NADH, and pyruvate are formed P P Glyceraldehyde-3-phosphate(G3P)  Step     A redox reaction generates NADH. 5 6 9 ENERGY PAYOFF PHASE NAD  NAD  P 6 6 P NADH NADH +H +H P P P P 1,3-Diphosphoglycerate  Steps     –      ATP and pyruvate are produced. 9 6 ADP ADP 7 7 ATP ATP P 3-Phosphoglycerate P P P 8 8 2-Phosphoglycerate H2O H2O P P Phosphoenolpyruvate(PEP) 9 9 ADP ADP ATP ATP Pyruvate

  41. Net Energy Yield from Glycolysis Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Glycolysis net yield is 2 ATP and 2 NADH

  42. Preparatory reactions before the Krebs cycle • Preparatory reactions • Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide • NAD+ is reduced pyruvate + coenzyme A + NAD+ acetyl-CoA + NADH + CO2 • One of the carbons from pyruvate is released in CO2 • Two carbons are attached to coenzyme A and continue on to the Krebs cycle

  43. + H+ NADH NAD+ CoA Pyruvate Acetyl CoA(acetyl coenzyme A) CO2 Coenzyme A Figure 6.8 Pyruvate is gets ready for the citric acid cycle • Prior to the citric acid cycle • Enzymes process pyruvate, releasing CO2 and producing NADH and acetyl CoA 2 1 3

  44. Krebs cycle • The acetyl units are oxidized to carbon dioxide • NAD+ and FAD are reduced Products: • Coenzyme A • 2 CO2 • 3 NADH • FADH2 • ATP

  45. Acetyl CoA CoA CoA CO2 2 CITRIC ACID CYCLE NAD+ 3 FADH2 3 FAD NADH + 3 H+ ADP + ATP P 0 The citric acid cycle (Krebs)completes the oxidation of organic fuel (glucose), generating many NADH and FADH2 molecules • In the citric acid cycle • The two-carbon acetyl part of acetyl CoA is oxidized Figure 6.9A

  46. Krebs Cycle or Citric Acid Cycle

  47. For each turn of the Krebs cycle • Two CO2 molecules are released (All of the carbon molecules in pyruvate end up in carbon dioxide) • Three NADH and one FADH2 (Coenzymes are reduced, they pick up electrons andhydrogen) • One molecule of ATP is formed for each turn so the net yield of ATP for the Krebs or Citric Acid cycle is 2 ATP molecules.

  48. What happened to co-enzymes (NAD and FAD) during the first two stages? Co-enzymes were reduced (gainedelectrons) • Glycolysis 2 NADH • Preparatory reactions 2 NADH • Krebs cycle 2 FADH2 + 6 NADH • Total 2 FADH2 + 10 NADH

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