Metabolism II

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Metabolism II
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• Nearly all of the energy needed by the human body
  is provided by the oxidation of carbohydrates and
  lipids. Whereas carbohydrates provide a readily
  available source of energy, lipids function
  primarily as an energy reserve.
• It is interesting to compare the relative amounts
  of energy provided by various biochemicals in a
  typical 154 lb male. The free glucose in the
  blood provides only a 40 kcal energy reserve --
  only enough to maintain body functions for a few
  minutes.

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• Glycogen remaining stored in the liver and
  muscles after an overnight fast, amounts to about
  600 kcal energy. Glycogen reserves can maintain
  body functions for about one day without new
  inputs of food. Protein (mostly in muscle)
  contains a substantial energy reserve of about
  25,000 kcal.
• Finally, lipid reserves containing 100,000 kcal
  of energy can maintain human body functions
  without food for 30-40 days with sufficient
  water. Lipids or fats represent about 24 pounds
  of the body weight in a 154 pound male.

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Lipid Metabolism

• Lipolysis breakdown of lipids for entry into
  TCA cycle
• Triglycerides are predominant lipid in body used
  for energy
• Stored in adipose tissue
• Glycerol backbone
• 3 fatty acids
• The first step in lipid metabolism is the
  hydrolysis of the lipid in the cytoplasm to
  produce glycerol and fatty acids.

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Glycerol

• Has a 3 carbon backbone that fatty acids attach
  to
• it is metabolized quite readily into an
  intermediate in glycolysis, dihydroxyacetone
  phosphate, which may be converted into pyruvic
  acid
• dihydroxyacetone may also be used in
  gluconeogenesis to make glucose-6-phosphate for
  glucose to the blood or glycogen depending upon
  what is required at that time.

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Fatty Acids

• Chain of hydrocarbons
• Can be saturated or unsaturated
• Fatty acids are oxidized to acetyl CoA in the
  mitochondria using the fatty acid spiral.

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Fatty Acid Spiral

• One turn of the fatty acid spiral produces ATP
  from the interaction of the coenzymes FAD (step
  1) and NAD (step 3) with the electron transport
  chain. Total ATP per turn of the fatty acid
  spiral is
• Step 1 - FAD into e.t.c. 2 ATPStep 3 - NAD
  into e.t.c. 3 ATP Total ATP per turn of spiral
  5 ATP

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• In order to calculate total ATP from the fatty
  acid spiral, you must calculate the number of
  turns that the spiral makes. Remember that the
  number of turns is found by subtracting one from
  the number of acetyl CoA produced.
• Example with Palmitic Acid 16 carbons 8
  acetyl groups
• Number of turns of fatty acid spiral 8-1 7
  turns
• ATP from fatty acid spiral 7 turns and 5 per
  turn 35 ATP. activation energy 1 ATP NET
  ATP from Fatty Acid Spiral 35 - 1 34 ATP

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Beta Oxidation

• The acetyl CoA produced from the fatty acid
  spiral enters the TCA cycle. When calculating ATP
  production, you have to show how many acetyl CoA
  are produced from a given fatty acid as this
  controls how many "turns" the citric acid cycle
  makes.
• Used palmitic acid (16 carbons) The fatty acid
  spiral ends with the production of 8 acetyl CoA

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• 1 ATP, 3 NADH, 1 FADH2 12 ATP per acetyl CoA
  in TCA cycle
• All NADH FADH2 will enter Electron Transport
  system

 Step  ATP produced
One acetyl CoA per turn C.A.C. 12 ATP
8 Acetyl CoA 8 turns C.A.C. 8 x 12 96 ATP
Fatty Acid Spiral 34 ATP
GRAND TOTAL  130 ATP
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• These events occur in liver and muscle. During
  sustained exercise the cells of slow twitch
  muscle fibers (which possess mitochondria)
  utilize ß-oxidation as the major source of ATP.

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Protein Metabolism

• Proteins make up the structural tissue for
  muscles and tendons, transport oxygen or
  hemoglobin, catalyze all biochemical reactions as
  enzymes, and regulate reactions as hormones. Our
  bodies must be able to synthesize the many
  proteins, amino acids, and other non-protein
  nitrogen containing compounds needed for growth,
  replacement, and repair. Proteins in excess are
  used to supply energy or build reserves of
  glucose, glycogen, or lipids.

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nitrogen or amino acid pool

• mixture of amino acids available in the cell
  derived from dietary sources or the degradation
  of protein. Since proteins and amino acids are
  not stored in the body, there is a constant
  turnover of protein. Some protein is constantly
  being synthesized while other protein is being
  degraded

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Synthesis of New Amino Acids

• these reactions can also be used to synthesize
  amino acids needed or not present in the diet. An
  amino acid may be synthesized if there is an
  available "root" ketoacid with a synthetic
  connection to the final amino acid. Since an
  appropriate "root" keto acid does not exist for
  eight amino acids, (lys, leu, ile, met, thr, try,
  val, phe), they are essential and must be
  included in the diet because they cannot be
  synthesized

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• if there are excess proteins in the diet those
  amino acids converted into pyruvic acid and
  acetyl CoA can be converted into lipids by the
  lipogenesis process. If carbohydrates are lacking
  in the diet or if glucose cannot get into the
  cells (as in diabetes), then those amino acids
  converted into pyruvic acid and oxaloacetic acids
  can be converted into glucose or glycogen.
• The hormones cortisone and cortisol from the
  adrenal cortex stimulate the synthesis of glucose
  from amino acids in the liver and also function
  as antagonists to insulin.

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oxidative deamination

• Deamination is also an oxidative reaction that
  occurs under aerobic conditions in all tissues
  but especially the liver. During oxidative
  deamination, an amino acid is converted into the
  corresponding keto acid by the removal of the
  amine functional group as ammonia and the amine
  functional group is replaced by the ketone group.
  The ammonia eventually goes into the urea cycle.

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