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Chapter 5

Chapter 5. Cell Respiration & Metabolism. 5-1. Chapter 5 Outline Glycolysis Aerobic Respiration Fat & Protein Metabolism. 5-2. Metabolism. Is all reactions in body that involve energy transformations Divided into 2 categories: Catabolism breaks down molecules & releases energy

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Chapter 5

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  1. Chapter 5 Cell Respiration & Metabolism 5-1

  2. Chapter 5 Outline • Glycolysis • Aerobic Respiration • Fat & Protein Metabolism 5-2

  3. Metabolism • Is all reactions in body that involve energy transformations • Divided into 2 categories: • Catabolism breaks down molecules & releases energy • Is primary source of energy for making ATP • Anabolism makes larger molecules & requires energy • Source of body’s large energy-storage compounds 5-3

  4. Glycolysis 5-4

  5. Glycolysis • Is metabolic pathway by which glucose is converted to 2 pyruvates • Does not require oxygen • Overall net equation is: • glucose + 2NAD + 2ADP + 2Pi  2 pyruvates + 2NADH + 2 ATP 5-5

  6. Glycolysis continued • Glycolysis is exergonic - produces net of 2ATPs & 2NADHs • However, glucose must be activated with 2ATPs (phosphorylation) before energy can be obtained • Phosphorylation traps glucose inside cell • Below can see 2ATPs added & 4 are produced for a net gain of 2 ATP Fig 5.1 5-6

  7. Glycolysis continued Fig 5.2 5-7

  8. Lactic Acid Pathway • To avoid end-product inhibition, NADHs produced in glycolysis need to give Hs away • In absence of O2, NADH gives its Hs to pyruvate creating lactic acid (anaerobic respiration) • Makes muscles feel fatigued Fig 5.3 5-8

  9. Lactic Acid Pathway continued • RCCs don't have mitochondria; use only lactic acid pathway • Occurs in skeletal & heart muscle when oxygen supply falls below critical level • During heavy exercise or vascular blockage 5-9

  10. Glycogenesis & Glycogenolysis • For osmotic reasons cells can't store many free glucoses • Instead store glucose as glycogen (glycogenesis) • Skeletal muscle & liver store lots of glycogen • Glycogenolysis clips glucose out of glycogen as glucose 6-phosphate • Phosphate groups trap molecules in cells 5-10

  11. Glycogenesis & Glycogenolysis continued • Skeletal muscles use trapped glucose-6-phosphate for own energy needs • Only liver has glucose-6-phosphatase that removes phosphate groups • So glucose can be secreted Fig 5.4 5-11

  12. Cori Cycle • Some skeletal muscle lactic acid goes to liver • Where it is converted back through pyruvate to glucose & glycogen • Called gluconeogenesis • Also can happen with amino acids & glycerol Fig 5.5 5-12

  13. Aerobic Respiration 5-13

  14. Aerobic Respiration • Begins when pyruvate formed by glycolysis enters mitochondria • C02 is clipped off pyruvate forming acetyl CoA (coenzyme Ais a carrier for acetic acid) • C02 goes to lungs • Energy in acetyl CoA is extracted during aerobic respiration in mitochondria Fig 5.6 5-14

  15. Krebs Cycle Fig 5.7 • Begins with acetyl CoA combining with oxaloacetic acid to form citric acid • In a series of reactions citric acid converted back to oxaloacetic acid to complete the pathway 5-15

  16. Krebs Cycle continued • Produces 1 GTP, 3 NADH, & 1 FADH2 • NADH & FADH2 carry electrons to Electron Transport Chain (ETC) 5-16

  17. Krebs Cycle continued Fig 5.8 5-17

  18. Electron Transport & Oxidative Phosphorylation • The electron transport chain is a linked series of proteins on the cristae of mitochondria • Proteins are FMN, coenzyme Q, & cytochromes Fig 3.10 5-18

  19. Electron Transport & Oxidative Phosphorylation continued • NADH & FADH2 from Krebs carry electrons to ETC • Which are then shuttled in sequence through ETC • NAD & FAD are regenerated to shuttle more electrons from Krebs Cycle to ETC 5-19

  20. Electron Transport & Oxidative Phosphorylation continued • As each protein in ETC accepts electrons it is reduced • When it gives electrons to next protein it is oxidized • This process is exergonic • Energy is used to phosphorylate ADP to make ATP • Called oxidative phosphorylation Fig 5.9 5-20

  21. Chemiosmotic theory Fig 5.10 • Energy gathered by ETC is used to pump H+s into mitochondria outer chamber • Creating high H+ concentration there • As H+s diffuse down concentration & charge gradient thru ATP synthase, & back into inner chamber, their energy drives ATP synthesis (Chemiosmotic theory) 5-21

  22. Function of Oxygen Fig 5.10 • Electrons added to beginning of ETC are passed along until reach end • Have to be given away or would stop ETC • O2 accepts these electrons & combines with 4H+s • O2 + 4 e- + 4 H+  2 H20 5-22

  23. ATP Formation • ATP can be made 2 ways: • Direct (substrate-level) phosphorylation • Where ATP is generated when bonds break • Both ATPs in glycolysis made this way • 2 ATPs/glucose in Kreb's made this way • Oxidative phosphorylation in Kreb's • Where ATP generated by ETC • 30-32 ATPs made this way 5-23

  24. ATP Formation continued • 3H+s pass thru ATP synthase to generate 1 ATP • This yields 36-38 ATPs/glucose • However some of these are used to pump ATPs out of mitochondria • So net yield is 30-32 ATPs/glucose • Really takes 4H+s to generate 1 exported ATP 5-24

  25. Production of ATP by ETC • 2.5 ATP produced for each pair of electrons NADH donates • 1.5 ATP produced for each pair of electrons FADH2 donates • Net of 26 ATP produced in ETC 5-25

  26. Net Production of ATP • 26 ATP produced in ETC • 2 from glycolysis • 2 from direct phosphorylation in Kreb’s • For total of 30 ATPs for each glucose 5-26

  27. 5-27

  28. Fat & Protein Metabolism 5-28

  29. Fats & Proteins as Energy Sources • Fats can be hydrolyzed to glycerol & fatty acids • These can be modified to run thru Kreb's • Proteins can be broken down to amino acids • Which can be deaminated & run thru Kreb's • These pathways can be used to interconvert carbohydrates, fats, & proteins 5-29

  30. Energy Storage • When more energy is taken in than consumed, ATP synthesis is inhibited • Glucose converted into glycogen & fat Fig 5.11 5-30

  31. Acetyl CoA • Is a common substrate for energy & synthetic pathways Fig 5.12 5-31

  32. Fat Synthesis (Lipogenesis) • Acetyl CoAs can be linked together to form fatty acids • Fatty acids + glycerol = Fat (triglycerides) • Occurs mainly in adipose & liver tissues • Fat is major form of energy storage in body • Yields 9 kilocalories/g • Carbs & proteins yield only 4/g 5-32

  33. Lipolysis • Is breakdown of fat into fatty acids & glycerol • Via hydrolysis by lipase • Acetyl CoAs from free fatty acids serve as major energy source for many tissues 5-33

  34. Acetyl CoA from Fat --Beta-Oxidation • Beta-oxidationclips acetyl CoAs off fatty acid chains • Which can be run thru Kreb's giving 10ATPs each • Plus -oxidation itself yields 4 ATPs Fig 5.13 5-34

  35. Brown Fat • Amount of brown fat greatest at time of birth • Major site for thermogenesis in the newborn • Brown fat produces uncoupling protein, causing H+ to leak out of inner mitochondrial membrane • Less ATP produced, causes electron transport system to be more active • Heat produced instead of ATP 5-35

  36. Ketone Bodies • Triglycerides are continually broken down & resynthesized • Ensures blood will contain fatty acids for aerobic respiration • During fasting & diabetes lots of fat is broken down • Causes high levels of ketone bodies • Fat metabolites • Gives breath an acetone smell 5-36

  37. Amino Acid Metabolism • Nitrogen (N) ingested primarily as protein • Which is used in body as amino acids • Excess is excreted mainly as urea 5-37

  38. Nitrogen (N) Balance • Nitrogen balance = N ingested minus N excreted • Positive N balance: more N ingested than excreted • Negative N balance: less N ingested than excreted • In healthy adults amount of N excreted = amount ingested • Excess amino acids can be converted into carbos & fat 5-38

  39. Essential & Non-essential Amino Acids • 20 amino acids used to build proteins • 12 can be produced by body • 8 must come from diet (= essential amino acids) 5-39

  40. Transamination • New amino acids can be obtained by transamination • Which is addition of -NH2 to pyruvate or Kreb's cycle ketones to make a new amino acid • Catalyzed by transaminase 5-40

  41. Transamination continued Fig 5.14 5-41

  42. Oxidative Deamination • Is process by which excess amino acids are eliminated • -NH2 is removed from glutamic acid, forming keto acid & ammonia • Ammonia is converted to urea & excreted • Keto acid goes to Kreb’s or to fat or glucose Fig 5.15 5-42

  43. Gluconeogenesis • Occurs when amino acids are converted to Keto acids, then pyruvate, then glucose 5-43

  44. Uses of Different Energy Sources • Different cells have different preferred energy substrates • Brain uses glucose as its major source of energy 5-44

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