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Chapter 6

Chapter 6. 0. How Cells Harvest Chemical Energy. 0. How Is a Marathoner Different from a Sprinter? Human muscles contain two different types of muscle fibers That perform differently under different conditions. 0. The different types of muscle fibers

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Chapter 6

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  1. Chapter 6 0 How Cells Harvest Chemical Energy

  2. 0 • How Is a Marathoner Different from a Sprinter? • Human muscles contain two different types of muscle fibers • That perform differently under different conditions

  3. 0 • The different types of muscle fibers • Function either aerobically, with oxygen, or anaerobically, without oxygen • Cellular respiration • Is the process by which cells produce energy aerobically

  4. INTRODUCTION TO CELLULAR RESPIRATION 0 • 6.1 Photosynthesis and cellular respiration provide energy for life • Cellular respiration makes ATP and consumes O2 • During the oxidation of glucose to CO2 and H2O

  5. Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts Glucose CO2 + + H2O O2 Cellular respiration in mitochondria ATP (for cellular work) Heat energy 0 • Photosynthesis uses solar energy • To produce glucose and O2 from CO2 and H2O Figure 6.1

  6. O2 Breathing CO2 Lungs O2 CO2 Bloodstream Muscle cells carrying out Cellular Respiration Glucose + O2 CO2 +H2O +ATP 0 • 6.2 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

  7. O2 CO2 C6H12O6 6 6 H2O ATPs + + 6 + Carbon dioxide Glucose Energy Oxygen gas Water 0 • 6.3 Cellular respiration banks energy in ATP molecules • Cellular respiration breaks down glucose molecules • And banks their energy in ATP Figure 6.3

  8. CONNECTION 0 • 6.4 The human body uses energy from ATP for all its activities • ATP powers almost all cellular and body activities Table 6.4

  9. 0 • 6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen • Electrons lose potential energy • During their transfer from organic compounds to oxygen

  10. 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

  11. Oxidation H + O 2H H O Dehydrogenase Reduction H+ NAD+ NADH + 2H + (carries 2 electrons) 2H+ 2e + 0 • Dehydrogenase removes electrons (in hydrogen atoms) from fuel molecules (oxidation) • And transfers them to NAD+ (reduction) Figure 6.5B

  12. 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 to O2 • Energy is released in small quantities Figure 6.5C

  13. STAGES OF CELLULAR RESPIRATION AND FERMENTATION 0 • 6.6 Overview: Cellular respiration occurs in three main stages • Cellular respiration • Occurs in three main stages

  14. 0 • Stage 1: Glycolysis • Occurs in the cytoplasm • Breaks down glucose into pyruvate, producing a small amount of ATP

  15. 0 • Stage 2: The citric acid cycle • Takes place in the mitochondria • Completes the breakdown of glucose, producing a small amount of ATP • Supplies the third stage of cellular respiration with electrons

  16. 0 • Stage 3: Oxidative phosphorylation • Occurs in the mitochondria • Uses the energy released by “falling” electrons to pump H+ across a membrane • Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP

  17. NADH High-energy electrons carried by NADH NADH FADH2 and OXIDATIVE PHOSPHORYLATION(Electron Transport and Chemiosmosis) GLYCOLYSIS CITRIC ACID CYCLE Glucose Pyruvate Mitochondrion Cytoplasm ATP CO2 CO2 ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation 0 • An overview of cellular respiration Figure 6.6

  18. H+ 2 + 2 NAD+ 2 NADH Glucose 2 Pyruvate + 2 2 P ATP 2 ADP 0 • 6.7 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

  19. Enzyme P Adenosine P P ATP ADP P Organic molecule(substrate) P 0 • Glycolysis produces ATP by substrate-level phosphorylation • In which a phosphate group is transferred from an organic molecule to ADP Figure 6.7B

  20. 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

  21. 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 Figure 6.7C

  22. + H+ NADH NAD+ CoA Pyruvate Acetyl CoA(acetyl coenzyme A) CO2 Coenzyme A Figure 6.8 • 6.8 Pyruvate is chemically groomed 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

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

  24. 0 • The two carbons are added to a four-carbon compound, forming citrate • Which is then degraded back to the starting compound

  25. CoA Acetyl CoA CoA 2 carbons enter cycle Oxaloacetate 1 Citrate + H+ NADH 5 CO2 leaves cycle NAD+ 2 CITRIC ACID CYCLE NAD+ +H+ Malate NADH + P ADP FADH2 4 ATP Alpha-ketoglutarate FAD 3 CO2 leaves cycle Succinate + H+ NAD+ NADH Step 2 4 Steps 1 3 Steps and 5 and Acetyl CoA stokes the furnace. NADH, ATP, and CO2 are generated during redox reactions. Redox reactions generate FADH2 and NADH. Figure 6.9B • For each turn of the cycle • Two CO2 molecules are released • The energy yield is one ATP, three NADH, and one FADH2

  26. 0 • 6.10 Most ATP production occurs by oxidative phosphorylation • Electrons from NADH and FADH2 • Travel down the electron transport chain to oxygen, which picks up H+ to form water • Energy released by the redox reactions • Is used to pump H+ into the space between the mitochondrial membranes

  27. . 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 0 • In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes • Driving the synthesis of ATP

  28. Cyanide, carbon monoxide Rotenone Oligomycin H+ H+ H+ ATPSynthase H+ H+ H+ H+ H+ H+ DNP FAD FADH2 1 + O2 2 H+ NADH NAD+ 2 H+ + ATP P ADP H+ H2O H+ Electron Transport Chain Chemiosmosis CONNECTION 0 • 6.11 Certain poisons interrupt critical events in cellular respiration • Various poisons • Block the movement of electrons • Block the flow of H+ through ATP synthase • Allow H+ to leak through the membrane Figure 6.11

  29. 0 • 6.12 Review: Each molecule of glucose yields many molecules of ATP • Oxidative phosphorylation, using electron transport and chemiosmosis • Produces up to 38 ATP molecules for each glucose molecule that enters cellular respiration Electron shuttleacross membrane Mitochondrion 2 2 NADH NADH Cytoplasm (or 2 FADH2) 2 2 6 FADH2 NADH NADH OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) GLYCOLYSIS 2 AcetylCoA 2 CITRIC ACIDCYCLE Glucose Pyruvate + about 34 ATP + 2 ATP + 2 ATP by substrate-level phosphorylation by oxidative phosphorylation by substrate-level phosphorylation About38 ATP Maximum per glucose: Figure 6.12

  30. 0 • 6.13 Fermentation is an anaerobic alternative to cellular respiration • Under anaerobic conditions, many kinds of cells • Can use glycolysis alone to produce small amounts of ATP

  31. 2 2 NADH 2 2 NAD+ NADH NAD+ GLYCOLYSIS P 2 ADP + 2 ATP 2 2 Pyruvate 2 Lactate Glucose 0 • In lactic acid fermentation • NADH is oxidized to NAD+ as pyruvate is reduced to lactate Figure 6.13A

  32. 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

  33. INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS 0 • 6.14 Cells use many kinds of organic molecules as fuel for cellular respiration

  34. Food, such aspeanuts Carbohydrates Fats Proteins Sugars Fatty acids Amino acids Glycerol Aminogroups OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis) CITRICACIDCYCLE AcetylCoA Pyruvate Glucose G3P GLYCOLYSIS ATP 0 • Carbohydrates, fats, and proteins can all fuel cellular respiration • When they are converted to molecules that enter glycolysis or the citric acid cycle Figure 6.14

  35. ATP needed to drive biosynthesis ATP GLUCOSE SYNTHESIS CITRIC ACID CYCLE Acetyl CoA Glucose Pyruvate G3P Amino groups Fatty acids Amino acids Sugars Glycerol Carbohydrates Proteins Fats Cells, tissues, organisms 0 • 6.15 Food molecules provide raw materials for biosynthesis • Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials • This process of biosynthesis • Consumes ATP Figure 6.15

  36. 0 • 6.16 The fuel for respiration ultimately comes from photosynthesis • All organisms • Can harvest energy from organic molecules • Plants, but not animals • Can also make these molecules from inorganic sources by the process of photosynthesis Figure 6.16

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