Fat Metabolism

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Fat Metabolism

• Fat, in the form of TG, is the major storage form
  of energy in humans (adipose cells)
• Excellent storage fuel for several reasons
• Energy-dense fuel yielding 9.13 kcal/gm
• TG is stored dry (unlike CHO)
• Fat supplies can last for weeks
• TG 1 glycerol and 3 fatty acids
• (oleic acid, palmitic acid, stearic acid,
  linoleic acid)

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Catabolism of TG molecule

• Mobilization The breakdown of adipose and
  intramuscular TG
• Circulation The transport of FFA from adipose to
  muscle
• Uptake The entry of FFAs into muscles from blood
• Activation raising the energy level of FFA
• Translocation The entry of activated fatty acids
  into mitochondria
• ß Oxidation The catabolism of acetyl-CoA of
  activated fatty acids and the production of
  reducing equivalents
• Mitochondrial Oxidation Krebs cycle and ETC

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• Beta Oxidation is a cyclic series of steps that
  breaks off successive pairs of carbon atoms from
  FFA, which are then used to form acetyl CoA
• Acetyl CoA is the common intermediate by which
  all foodstuffs enter
• Number of cycles depends upon the number of
  carbons (14-24 carbons)
• ATP is used for activation produces no ATP
  directly

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ATP Production from Fatty Acids

• of ATP produced from the breakdown of fat
  depends on which fatty acid is utilized
• Palmitate is a 16-carbon fatty acid and yields
  129 ATP
• Stearate is a 18-carbon fatty acid and yields 146
  ATP
• These calculations apply to a single fatty acid
• For the mixture that comprises human adipose
  tissue the ATP yield is 138 molecules of ATP per
  molecule of fatty acid, or 414 ATP per TG

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Hormone-Sensitive Lipase
TG
Glycerol

Need this as a precursor to synthesize and
metabolize fat
Glucose

FFA
FAT BURNS IN A CARBOHYDRATE FLAME
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Protein Metabolism

• Proteins are digested and absorbed as amino acids
  
• used predominantly as building blocks, not as a
  source of energy
• Before amino acids can be used as a fuel and
  enter the pathways at any place
• Transfer of the NH2 amino group from an amino
  acid to a keto acid or excretion in the urine,
  respectively

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ATP Production from Amino Acids

• Amino Acid derivatives are ultimately utilized as
  pyruvate or acetyl CoA
• ATP production count is the same as for glucose
  from that point on, except that it is not
  doubled.
• Pyruvate would produce 15 ATP (3 1 9 2
  15)
• Acetyl CoA would produce 12 ATP (eliminate NADH
  H step)

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Enzymes catalyze reactions by lowering the energy
of activation
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Rate-limiting enzyme in a simple metabolic pathway
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Regulation of Cellular Respiration ATP
Production

• Intracellular (Rate-limiting steps)
• ATP-PC system Creatine Kinase
• Glycolysis Phosphofructose Kinase
• Krebs cycle Isocitrate Dehydrogenase
• ETC - Cytochrome oxidase
• Extracellular
• Gluconeogenesis - necessary to maintain blood
  glucose levels during exercise
• Glycerol-glucose cycle
• Cori cycle
• Felig cycle

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Fuel Utilization at Rest and during Exercise
Triglycerides provide greatest source of
potential energy Very little carbohydrate is
stored Exercise has a major impact on how long
each fuel can supply energy
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