MetabolismHow do we obtain energy from foods

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MetabolismHow do we obtain energy from foods?

• Susan Algert, Ph.D., R.D.

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Metabolism

• Human body releases energy from chemical bonds in
  nutrients the body uses for fuel.
• As bonds break they release energy
• During metabolism, energy, water and carbon
  dioxide are released

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Energy yielding nutrients

• From carbohydratesglucose
• From lipids (trigylcerides)glycerol and fatty
  acids
• From proteinsamino acids

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The Cell

• Cells are work centers of metabolism
• Cells have similar structures
• Two basic partsnucleus and cytoplasm
• Mitochondria are power generators that contain
  energy generating pathways

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Breaking down glucose for energy--aerobic

• 6-C glucose split in half making two 3-Carbon
  compounds
• Glycolysis means glucose splitting
• -Carbon compounds become 2 pyruvates
• Pyruvates will break down further to form ATP and
  heat

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Glucose retrieval via the Cori cycle--anaerobic

• When less oxygen is available, pyruvate is
  converted to lactic acid
• Liver can convert lactic acid to glucose in a
  recycling process
• Pathway is muscle glycogen to glucose to pyruvate
  to lactic acid ( in liver) to glucose to glycogen

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Pyruvate to Acetyl Co-A

• Irreversible step
• Aerobic
• Acetyl Co A to Carbon Dioxide via the TCA cycle
• Electron Transport Chain
• Acetyl Co-A to fat

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Pyruvate is pivotal

• ATP levels are lowmetabolic pathways flow toward
  the production of ATP
• Depending on O-2 ATP routes pyruvate to acetyl
  Co-A or lactate
• ATP is abundant pyruvate converted to
  oxaloacetate or amino acid alanine oxaloacetate
  converted to glucose and then glycogen

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Acetyl Co-A at the crossroads

• Breakdown pathways for glucose, fatty acids and
  some amino acids converge at acetyl-CoA.
• Acetyl Co-A cannot return to pyruvate, but enters
  energy making pathways
• Acetyl Co-A can also make ketone bodies and fatty
  acids

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Glycerol and fatty acids

• Glycerol to pyruvate
• Fatty acids to Acetyl Co-A
• Beta oxidation
• Glucose not retrievable from fatty acids
• Breakdown of acetyl-Co-A
• Fat burns in flame of carbohydrate

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When a person draws on stores

• Fat used to fuel brain
• Acetyl Co-A fragments from fatty acids combine to
  produce ketone bodies
• Ketone bodies can provide some fuel for brain
  cells
• When ketone bodies contain an acid group they are
  called keto acids (COOH)

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Energy Compounds

• ATP used to power cellular functions
• NADH and FADH-2 carry energy for synthesis of ATP
• NADPH delivers energy for biosynthesis

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Amino Acid Catabolism

• Amino acids are deaminated and enter TCA cycle
• Amino acids used to make pyruvate can make
  glucose
• Amino acids that make Acetyl Co-A provide energy
  or body fat but not glucose

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Energy retrievable from amino acids-

• Glucogenic amino acids- a.a. broken down into
  pyruvate or intermediate of the TCA cycle
  gluconeogenesis
• Ketogenic amino acidsan a.a.a broken down into
  acetyl CoA which can be converted into ketone
  bodies

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Transamination

• Transfer of amino group from one amino acid to a
  keto acid, producing a new non essential amino
  acid and a keto acid

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Electron Transport Chain

• Series of proteins that serve as electron
  carriers
• Mounted in sequence on membrane inside
  mitochondria
• Carriers receive electrons, it passes electrons
  and gives up energy until end when any usable
  energy has captured bodys ATP molecules

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TCA and ETC

• Bodys most efficient means of capturing the
  energy from nutrients and transferring it into
  the bonds of ATP
• Last step of ETC low energy electrons with H
  atoms combine with O2 from the lungs to make H2O

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Which fuels can make glucose

• Parts of protein and fat that can make pyruvate
  can provide glucose parts that make acetyl Co A
  cannot, but provide fat
• Glucose is needed to fuel CNS and red blood cells
• If there is not enough glucose the body will
  break down protein

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Making glucose on low Carb diets

• Fat delivers mostly acetyl, so that you need to
  break down protein tissue to make glucose
• High protein diets make your body convert protein
  to glucose and convert ammonia to urea in the
  liver
• Urea is excreted via the kidneys
• Water is needed to excrete urea

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Energy yielding nutrients-fat provides most kcals
per gram

• Nearly all bonds in a fatty acid are between
  carbons and hydrogens
• Oxygen can be added to all of them (making CO2
  and H2O)
• Energy in bonds is released as they are oxidized
• Glucose has less potential for oxidation as
  oxygen is already bonded to each C

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Feasting

• Surplus proteinDeaminate and convert to acetyl
  Co-A and fat
• Surplus carbohydrate--Glycogen
• Surplus fat--Lipogenesis

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