Outline of Campbell Biology Chapter 9

VII. COMPARISON OF AEROBIC AND ANAEROBIC CATABOLISM

  1. Introduction
    1. There are three major catabolic processes for harvesting food's chemical energy
      1.  
      2. aerobic respiration
      3. anaerobic respiration
      4. fermentation.
    2. These processes:
      1. Are similar in that the high energy electrons from substrate (e.g. glucose) oxidation are transferred to NAD+.
      2. Differ in the ultimate fate of high energy electrons stored in NADH.
  2. Cellular respiration includes all types of catabolism that use electron transport chains to make ATP, regardless of the substance used as the final electron acceptor. It also includes the Krebs cycle or some modification of the Krebs cycle.
  3. Aerobic respiration occurs only in the presence of oxygen. This process:
    1. Uses an electron transport chain to make ATP.
    2. Uses oxygen as the final electron acceptor.
    3. Produces most ATP by oxidative phosphorylation and some ATP by substrate-level phosphorylation.
    4. Is used by plants and animals.
  4. Anaerobic respiration is a catabolic process that does not require the presence of oxygen. This process:
    1. Uses an electron transport chain to make ATP.
    2. Uses a substance other than free oxygen as a final electron acceptor (e.g. NO3-, SO42-, or CO32-).
    3. Produces most ATP by oxidative phosphorylation and some by substrate-level phosphorylation.
    4. Occurs in a few bacterial groups that exist in anaerobic environments.
  5. Fermentation operates not only without electron transport chains, but without the Krebs cycle as well.
    1. No oxygen is required.
    2. The final electron acceptor is an organic substrate such as pyruvic acid or some derivative of pyruvic acid.
    3. ATP is produced by substrate level phosphorylation only.
    4. This process is less efficient than respiration. Respiration yields 18 times more ATP per glucose than fermentation.
  6. Organisms can be classified based upon the effect oxygen has on growth and metabolism.
    1. Strict (obligate) aerobes = Organisms that require oxygen for growth and as the final electron acceptor for aerobic respiration.
    2. Strict (obligate) anaerobes = Microorganisms that only grow in the absence of oxygen and are, in fact, poisoned by it.
    3. Facultative anaerobes = Organisms capable of growth in either aerobic or anaerobic environments.
      1. Yeasts, many bacteria and mammalian muscle cells are facultative anaerobes.
      2. Some facultative anaerobes make ATP only by fermentation in the absence of oxygen, and make ATP by respiration in presence of oxygen.
      3. Glycolysis is common to fermentation and respiration. In some facultative anaerobes, the fate of pyruvic acid will be either fermentation or respiration depending upon the presence of absence of oxygen.
  7. Evolutionary Significance of Glycolysis:
    1. The first prokaryotes probably produced ATP by glycolysis. Evidence includes the following:
      1. Glycolysis does not require oxygen, and the oldest known bacterial fossils date back to three-and-a-half billion years ago when oxygen was not present in the atmosphere.
      2. Glycolysis is the most widespread metabolic pathway, so it probably evolved early.
      3. Glycolysis occurs in the cytoplasm and does not require membrane- bound organelles. Eukaryotic cells with organelles probably evolved about two billion years after prokaryotic cells.