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15.) Fatty acid degradation: intracellular localization, role of carnitine, reactions, ATP produced, regulation (role of carnitine palmitoyltransferase I). Fates of propionyl CoA.

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  1. Front
    Fatty acid degradation
    Back
    Mainly means β-oxidation of fatty acids
  2. Front
    Products of β-oxidation
    Back
    Acetyl-CoA, NADH, and FADH2
  3. Front
    How β-oxidation products make ATP
    Back
    Through the TCA cycle and electron transport chain
  4. Front
    High-yield sequence of fatty acid degradation
    Back
    Activation makes fatty acyl-CoA, the carnitine shuttle moves long-chain fatty acyl groups into mitochondria, β-oxidation shortens them, and acetyl-CoA enters TCA or in liver can go toward ketogenesis
  5. Front
    Main intracellular location of β-oxidation
    Back
    Mitochondrial matrix
  6. Front
    Lecture statement about fatty acid oxidation
    Back
    Fatty acid oxidation is a mitochondrial pathway
  7. Front
    Special location for very long-chain fatty acid oxidation
    Back
    Peroxisomes
  8. Front
    High-yield localization summary
    Back
    β-Oxidation occurs mainly in the mitochondrial matrix, but very long-chain fatty acids can begin oxidation in peroxisomes
  9. Front
    Peripheral tissues important for fatty acid oxidation
    Back
    Heart, muscle, kidney, and liver
  10. Front
    Tissues emphasized as important users of fatty acids
    Back
    Heart, skeletal muscle, kidney, and liver
  11. Front
    Substrate for β-oxidation
    Back
    Fatty acyl-CoA
  12. Front
    Why activation is required before β-oxidation
    Back
    β-Oxidation uses fatty acyl-CoA, not a free fatty acid
  13. Front
    High-yield substrate fact for β-oxidation
    Back
    β-Oxidation uses acyl-CoA
  14. Front
    Why carnitine is needed in fatty acid oxidation
    Back
    Long-chain fatty acids are activated outside the matrix, β-oxidation occurs in the matrix, and the inner mitochondrial membrane is impermeable to CoA
  15. Front
    Main function of carnitine
    Back
    Transports long-chain acyl groups into the mitochondrial matrix
  16. Front
    High-yield carnitine fact
    Back
    Carnitine transports long-chain acyl groups into the mitochondrial matrix
  17. Front
    Step 1 of the carnitine shuttle
    Back
    CPT I transfers the acyl group from CoA to carnitine to form acylcarnitine
  18. Front
    Location of CPT I
    Back
    Outer mitochondrial membrane
  19. Front
    Reaction catalyzed by CPT I
    Back
    Fatty acyl-CoA → acylcarnitine
  20. Front
    Step 2 of the carnitine shuttle
    Back
    Carnitine-acylcarnitine translocase moves acylcarnitine across the inner mitochondrial membrane
  21. Front
    Step 3 of the carnitine shuttle
    Back
    CPT II transfers the acyl group from carnitine back to CoA in the matrix
  22. Front
    Location of CPT II
    Back
    Inner mitochondrial membrane
  23. Front
    Result of CPT II reaction
    Back
    Fatty acyl-CoA is regenerated in the matrix
  24. Front
    Step 4 of the carnitine shuttle
    Back
    Free carnitine returns to the cytosolic side by the shuttle system
  25. Front
    High-yield summary of the carnitine shuttle
    Back
    CPT I makes acylcarnitine, translocase moves it, and CPT II remakes acyl-CoA in the matrix
  26. Front
    Fatty acids that do not require carnitine for mitochondrial entry
    Back
    Fatty acids with 12 carbons or fewer
  27. Front
    High-yield chain-length exception
    Back
    Long-chain fatty acids require carnitine, whereas short- and medium-chain fatty acids do not
  28. Front
    Four recurring reactions of β-oxidation
    Back
    Oxidation, hydration, oxidation, and thiolysis
  29. Front
    First reaction of β-oxidation
    Back
    Oxidation producing FADH2
  30. Front
    Second reaction of β-oxidation
    Back
    Hydration
  31. Front
    Third reaction of β-oxidation
    Back
    Oxidation producing NADH
  32. Front
    Fourth reaction of β-oxidation
    Back
    CoA-dependent thiolytic cleavage releasing acetyl-CoA and a fatty acyl-CoA shortened by 2 carbons
  33. Front
    High-yield order of β-oxidation reactions
    Back
    Oxidation, hydration, oxidation, thiolysis
  34. Front
    Products of each cycle of β-oxidation
    Back
    1 FADH2, 1 NADH, 1 acetyl-CoA, and a fatty acyl-CoA shortened by 2 carbons
  35. Front
    Special final step logic for even-chain saturated fatty acids
    Back
    The last cleavage gives 2 acetyl-CoA
  36. Front
    Number of β-oxidation cycles for a saturated even-chain fatty acid with n carbons
    Back
    (n/2) − 1
  37. Front
    Number of acetyl-CoA molecules formed from a saturated even-chain fatty acid with n carbons
    Back
    n/2
  38. Front
    Number of β-oxidation cycles for palmitate (16:0)
    Back
    7
  39. Front
    Number of acetyl-CoA molecules formed from palmitate (16:0)
    Back
    8
  40. Front
    β-Oxidation products from palmitate (16:0)
    Back
    7 FADH2, 7 NADH, and 8 acetyl-CoA
  41. Front
    ATP from 7 FADH2 in palmitate oxidation
    Back
    10.5 ATP
  42. Front
    ATP from 7 NADH in palmitate oxidation
    Back
    17.5 ATP
  43. Front
    ATP from 8 acetyl-CoA in palmitate oxidation
    Back
    80 ATP
  44. Front
    Total ATP from palmitate oxidation before activation cost
    Back
    108 ATP
  45. Front
    Activation cost for palmitate oxidation
    Back
    2 ATP equivalents
  46. Front
    Net ATP yield from palmitate oxidation with lecture values
    Back
    106 ATP
  47. Front
    Older textbook ATP values for oxidative phosphorylation
    Back
    NADH = 3 ATP and FADH2 = 2 ATP
  48. Front
    Older textbook net ATP yield from palmitate
    Back
    Lippincott older accounting gives 129 ATP net
  49. Front
    ATP convention used by the lecture
    Back
    NADH = 2.5 ATP and FADH2 = 1.5 ATP
  50. Front
    6-carbon saturated fatty acid β-oxidation example
    Back
    2 cycles, 2 FADH2, 2 NADH, and 3 acetyl-CoA
  51. Front
    ATP from a 6-carbon saturated fatty acid before activation cost
    Back
    38 ATP
  52. Front
    Net ATP from a 6-carbon saturated fatty acid with lecture values
    Back
    36 ATP
  53. Front
    Main regulatory point of β-oxidation
    Back
    CPT I
  54. Front
    Key regulatory fact about CPT I
    Back
    Malonyl-CoA inhibits CPT I
  55. Front
    Why CPT I is the key regulatory step
    Back
    It controls entry of long-chain fatty acyl groups into the mitochondrial matrix, which is required for β-oxidation
  56. Front
    Why malonyl-CoA inhibition of CPT I is important
    Back
    When fatty acid synthesis is active, malonyl-CoA prevents newly synthesized fatty acids from entering mitochondria for degradation
  57. Front
    High-yield regulation summary for β-oxidation
    Back
    Malonyl-CoA inhibits CPT I, so fatty acid synthesis and β-oxidation do not run strongly at the same time
  58. Front
    Other β-oxidation regulation noted by Lippincott
    Back
    β-Oxidation is regulated by the acetyl-CoA/CoA ratio
  59. Front
    Effect of high acetyl-CoA on β-oxidation thiolase
    Back
    When acetyl-CoA is high, the thiolase reaction slows
  60. Front
    General factors affecting fatty acid oxidation in the lecture
    Back
    Tissue specificity, number of mitochondria, substrate availability, carnitine concentration, ATP requirement, FAD, and NAD+
  61. Front
    Importance of β-oxidation in fasting
    Back
    Albumin-bound free fatty acids rise and fatty acid oxidation increases
  62. Front
    Role of acetyl-CoA produced by β-oxidation in liver
    Back
    Supports gluconeogenesis and can also support ketone body formation
  63. Front
    High-yield fasting fact for β-oxidation
    Back
    β-Oxidation is especially important in fasting
  64. Front
    Difference in odd-chain fatty acid oxidation
    Back
    Oxidation proceeds normally until the last 3 carbons remain
  65. Front
    Final 3-carbon product of odd-chain fatty acid oxidation
    Back
    Propionyl-CoA
  66. Front
    Step 1 of propionyl-CoA metabolism
    Back
    Propionyl-CoA → D-methylmalonyl-CoA by propionyl-CoA carboxylase
  67. Front
    Requirements for propionyl-CoA carboxylase
    Back
    ATP, biotin, and bicarbonate or CO2
  68. Front
    Step 2 of propionyl-CoA metabolism
    Back
    D-methylmalonyl-CoA → L-methylmalonyl-CoA by methylmalonyl-CoA epimerase
  69. Front
    Step 3 of propionyl-CoA metabolism
    Back
    L-methylmalonyl-CoA → succinyl-CoA by methylmalonyl-CoA mutase
  70. Front
    Cofactor required by methylmalonyl-CoA mutase
    Back
    Vitamin B12 (deoxyadenosylcobalamin)
  71. Front
    Final product of propionyl-CoA metabolism
    Back
    Succinyl-CoA
  72. Front
    Pathway entered by succinyl-CoA
    Back
    TCA cycle
  73. Front
    Why propionyl-CoA matters metabolically
    Back
    Succinyl-CoA is a TCA intermediate, so odd-chain fatty acids can contribute glucogenic carbon
  74. Front
    High-yield odd-chain fatty acid fact
    Back
    Odd-chain fatty acids are partly glucogenic because propionyl-CoA is converted to succinyl-CoA
  75. Front
    Cofactors to know for the carnitine shuttle
    Back
    Carnitine, CPT I, translocase, and CPT II
  76. Front
    Cofactors to know for the propionyl-CoA pathway
    Back
    Biotin for propionyl-CoA carboxylase and vitamin B12 for methylmalonyl-CoA mutase
  77. Front
    MCAD deficiency
    Back
    Most common inborn error of β-oxidation
  78. Front
    Chain lengths mainly affected in MCAD deficiency
    Back
    Fatty acids with 6 to 10 carbons
  79. Front
    Major consequences of MCAD deficiency
    Back
    Severe hypoglycemia and hypoketonemia
  80. Front
    Important treatment principle for MCAD deficiency
    Back
    Avoidance of fasting
  81. Front
    Effect of carnitine deficiency
    Back
    Decreases the ability to use long-chain fatty acids as fuel
  82. Front
    Effect of CPT I deficiency
    Back
    Strongly affects liver fasting metabolism and can cause severe hypoglycemia
  83. Front
    Effect of CPT II deficiency
    Back
    Often presents with muscle weakness and myoglobinuria after prolonged exercise
  84. Front
    Super high-yield localization fact for β-oxidation
    Back
    β-Oxidation occurs mainly in the mitochondrial matrix
  85. Front
    Super high-yield substrate fact
    Back
    The substrate for β-oxidation is fatty acyl-CoA
  86. Front
    Super high-yield transport fact
    Back
    Long-chain fatty acids require the carnitine shuttle to enter mitochondria
  87. Front
    Super high-yield CPT I fact
    Back
    CPT I is on the outer mitochondrial membrane and forms acylcarnitine
  88. Front
    Super high-yield CPT II fact
    Back
    CPT II regenerates acyl-CoA in the matrix
  89. Front
    Super high-yield malonyl-CoA fact
    Back
    Malonyl-CoA inhibits CPT I
  90. Front
    Super high-yield β-oxidation reaction sequence
    Back
    Oxidation, hydration, oxidation, thiolysis
  91. Front
    Super high-yield product yield per β-oxidation cycle
    Back
    Each cycle yields 1 FADH2, 1 NADH, and 1 acetyl-CoA except for the terminal cleavage logic where the final step gives 2 acetyl-CoA
  92. Front
    Super high-yield palmitate oxidation facts
    Back
    Palmitate gives 7 cycles, 8 acetyl-CoA, 7 NADH, 7 FADH2, and 106 ATP net with lecture values
  93. Front
    Super high-yield odd-chain fatty acid fact
    Back
    Odd-chain fatty acids end with propionyl-CoA, which becomes succinyl-CoA using biotin and B12
  94. Front
    Cheat-sheet localization of β-oxidation
    Back
    Main site is mitochondrial matrix, important tissues are liver, muscle, heart, and kidney, and very long-chain fatty acids can involve peroxisomes
  95. Front
    Cheat-sheet carnitine shuttle
    Back
    Long-chain fatty acids need carnitine, CPT I converts acyl-CoA to acylcarnitine, translocase moves it, CPT II regenerates acyl-CoA in the matrix, and malonyl-CoA inhibits CPT I
  96. Front
    Cheat-sheet β-oxidation reactions
    Back
    Oxidation producing FADH2, hydration, oxidation producing NADH, and thiolysis releasing acetyl-CoA
  97. Front
    Cheat-sheet palmitate yield
    Back
    7 cycles, 8 acetyl-CoA, 7 NADH, 7 FADH2, and 106 ATP net with lecture values
  98. Front
    Cheat-sheet propionyl-CoA fate
    Back
    Propionyl-CoA → D-methylmalonyl-CoA by propionyl-CoA carboxylase using biotin and ATP → L-methylmalonyl-CoA → succinyl-CoA by methylmalonyl-CoA mutase using B12, then enters the TCA cycle and makes odd-chain fatty acids partly glucogenic

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