How energy is derived from food.

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How energy is derived from food.

• AGRI 6203

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Cellular Respiration

• Process of oxidizing food
• energy released
• captured in ATP
• Two phases
• glycolysis
• breakdown of glucose to pyruvic acid
• oxidation of pyruvic acid

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Glycolysis

• in eukaryotes, it occurs in the cytosol.
• C6H12O6 2NAD -gt 2C3H4O3 2NADH 2H
• The free energy stored in 2 molecules of pyruvic
  acid is somewhat less than that in the original
  glucose molecule.
• Some of this difference is captured in 2
  molecules of ATP.

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Glycolysis
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Fates of Pyruvic Acid in Yeast

• Pyruvic acid is decarboxylated and reduced by
  NADH to form a molecule of carbon dioxide and one
  of ethanol.
• C3H4O3 NADH H -gt CO2 C2H5OH NAD
• This accounts for the bubbles and alcohol in,
  for examples, beer and champagne.
• The process is called alcoholic fermentation.
• The process is energetically wasteful because so
  much of the free energy of glucose (some 95)
  remains in the alcohol (a good fuel!).

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Fate of pyruvic acid in muscles

• Pyruvic acid is reduced by NADH forming a
  molecule of lactic acid.
• C3H4O3 NADH H -gt C3H6O3 NAD
• The process is called lactic acid fermentation.
• The process is energetically wasteful because so
  much free energy remains in the lactic acid
  molecule. (It can also be debilitating because of
  the drop in pH of overworked muscles.)

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Fate of pyruvic acid in mitochondria

• Pyruvic acid is oxidized completely to form
  carbon dioxide and water.
• The process is called cellular respiration.
• Approximately 40 of the energy in the original
  glucose molecule is trapped in molecules of ATP.

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Mitochondrion
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Mitochondrion

• Outer membrane
• integral membrane proteins
• form channels
• Inner membrane - 5 complexes
• NADH dehydrogenase
• succinate dehydrogenase
• cytochrome c reductase
• cytochrome c oxidase
• ATP synthase

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Citric Acid Cycle

• Each of the 3 carbons present in pyruvate that
  entered the mitochondrion leaves as a molecule of
  CO2
• at 4 steps in the cycle, a pair of (2e-) is
  removed and transferred to NAD reducing to NADH
  H
• at one step, a pair of electrons is removed from
  succinic acid and reduces FAD to FADH2
• one GTP (ATP equivalent is produced)

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The Respiratory Chain- Function of the four
integral membrane proteins

• NADH (FADH2) - stepwise transfer of electrons to
  ________ atoms to form _______.
• Harness the energy released by e- transfer to the
  pumping of protons (H) from the matrix to
  intermembrane space

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• Protons are pumped a 3 complexes
• NADH dehydrogenase complex
• cytochrome c reductase complex
• cytochrome c oxidase complex
• an average of three protons are pumped out at
  each complex as each pair of electrons passes
  through it
• 9 protons are pumped for each pair of electrons
  from NADH 6 from each pair from FADH2

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• The gradient of protons formed across the inner
  membrane by this process forms a miniature
  battery
• protons can flow back down this gradient,
  reentering the matrix, only through ATP synthase,
  another complex of integral protiens in the inner
  membrane

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Chemiosmosis in mitochondria

• Energy from electrons is harnessed by
• NADH dehydrogenase complex
• cytochrome c reductase complex
• cytochrome c oxidase complex
• the complexes pump protons against their gradient
  from the matrix into the inner membrane space
• a strong diffusion gradient is set up, the only
  exit of these protons is through ATP synthase
  complex

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Sources
Kimballs Biology Pages The Biology
Project Principles of Biochemisrty, Lehniger, 1982