Biology%20107%20Cellular%20Respiration

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Biology 107Cellular Respiration

• October 3, 2003

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Aerobic Respiration Occurs in the Eukaryotic
Mitochondrion and Includes the Krebs Cycle and
the Electron Transport Chain/Oxidative
Phosphorylation
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Pyruvate is Converted into Acetyl CoA to Enter
the Krebs Cycle
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Pyruvate is Transported into the Mitochondrion
and Converted to the 2-Carbon Acetyl CoA
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Steps of the Krebs Cycle
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General Organization of the Electron Transport
Chain
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Electron Transport Chain Establishes a H
Gradient Across the Inner Membrane
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The Movement of H Down Its Concentration
Gradient Generates ATP
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Summary of Cellular Respiration
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Catabolic Pathways
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Catabolic Pathways
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Example of Regulation Mechanisms for Catabolic
Pathways
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Cellular Respiration II

• Student Objectives As a result of this lecture
  and the assigned reading, you should understand
  the following
• Respiration occurs in two (2) stages 1) the
  Krebs cycle (citric acid cycle) and 2) the
  terminal electron transport chain.
• In eukaryotes these respiration reactions take
  place in mitochondria.
• 3. Some enzymes of the Krebs cycle are in the
  matrix of mitochondria other enzymes of the
  Krebs cycle and the enzymes of the electron
  transport system are in the membrane of the
  cristae of the inner membrane. The outer
  membrane is relatively permeable, while the inner
  membrane restricts passage of most molecules and
  ions, including protons (H ions).

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Cellular Respiration II

• Compared to glycolysis, the Krebs cycle pays off
  big energy dividends to the cell.
• a. Each turn of the cycle makes 1 ATP molecule
  (by substrate level phosphorylation) and 4 other
  energy-rich molecules (3NADH and 1 FADH2).
• b. Since two molecules of acetyl CoA are
  processed for each glucose precursor, the total
  yield is 2ATP, 6NADH, and 2 FADH2 (compared to
  the total of 2ATP and 2NADH molecules of
  glycolysis).
• 5. No oxygen is required for the Krebs cycle.

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Cellular Respiration II

• After the Krebs cycle is completed, glucose is
  completely oxidized, but most of the energy is
  stored in electrons moved from carbon atoms to
  the electron carriers NAD and FAD.
• In terminal electron transport, the high energy
  electrons stored in the NADH and FADH2 carriers
  are passed step-by-step to successively lower
  energy carriers embedded in the inner membrane of
  the mitochondrion until the electrons are finally
  accepted by the low energy level oxygen atom.
• As the electrons are passed down the electron
  transport chain, H are transported from the
  matrix across the inner mitochondrial membrane to
  the intermembrane space and a concentration
  gradient of hydrogen ions is produced.

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Cellular Respiration II

• The theory of chemiosmotic coupling explains how
  the concentration gradient of H is used to
  generate energy to make ATP.
• a. The enzyme complex ATP synthase synthesizes
  ATP using the energy stored in the concentration
  gradient of H ions (i.e., protons) across the
  inner membrane, which is relatively impermeable
  to H.
• b. The H ions tend to move down their
  concentration gradient toward the matrix of the
  mitochondrion. Movement through the ATP
  synthase is used to generate the ATP from ADP and
  inorganic phosphate.
• 10. The process of generating ATP from the
  electron transport chain is called oxidative
  phosphorylation.

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Cellular Respiration I

1. Fats, complex carbohydrates, and proteins may be
   funneled into glycolysis or the Krebs cycle. The
   most common convergent point is acetyl CoA.
2. In prokaryotic cells (which lack mitochondria)
   the oxidative reactions are distributed between
   the cytoplasm and the plasma membrane.