Lecture Outline:

1. Metabolism: The sum total of all the chemical reactions occurring in a cell. Two components of metabolism;

• Catabolism- chemical reactions that are degradative in function, and are regarded as carbon consuming and energy generating.
• anabolism- chemical reactions that are building in function, carbon generating, and require an expenditure of energy. Anabolic reactions are also referred to as biosynthetic reactions. Anabolism and catabolism go hand-in-hand.

2. Essential building blocks required by all cells:

• 11-12 precursor molecules- chemicals from which all other cellular chemicals are derived.
  
• reducing power- all cells require a source of protons and/or electrons. Electrons/protons can not exit alone, but must be associated with carrier molecules like NAD⁺, NADP⁺, and FAD⁺.
  
• metabolic energy- most often think of chemical energy, namely ATP (Fig. 2.10), but cells also need electrochemical energy or proton motive force.

3. Role of enzymes in metabolism: enzymes are biological catalysts which are neither consumed nor changed in a chemical reaction. A series of enzyme mediated reactions that convert a specific starting substance(s), substrate(s), to a specific product(s), end-product(s), is referred to as a metabolic pathway.

4. Example of two types of chemical reactions occurring within cells:

• Phosphorylation-
  • substrate level phosphorylation is one example in which a "high energy" phosphate group is transfered from one molecule to another ("high energy" phosphate group is retained). Fig. 6.6
    
• Oxidation Reduction reactions-
  • chemically speaking, an oxidation reaction is defined as the removal of an electron from a substance, and a reduction reaction the addition of an electron to a substance. Can not have one without other. The substance that is giving up its electron(s) is called the reducing agent or reductant, and the substance accepting electron(s) the oxidizing agent or oxidant.
    
  • In biology frequently an oxidation/reduction reaction involves the addition or removal of a pair of electrons or a pair of electrons and protons or the equivalent of two hydrogen atoms.
    
  • different substances have different inherent tendencies to give up or accept electrons/protons. Whether a substance gives up or accepts electrons/protons dependents on what it reacts with.
    
  • transfer of electrons or electron/protons from one carrier to the next releases energy, this can be used to establish an electrochemical gradient (proton gradient) accross membrane that can be used to make ATP.

5. Bacterial Metabolism: As a group, bacteria can carry out 3 types of metabolism: FERMENTATION, RESPIRATION (aerobic and/or anaerobic), and PHOTOSYNTHESIS (will not be held responsible for). Depending on the type of metabolism that is carried out, varying amounts of metabolic energy are generated. Which type of metabolism generates the most and the least amount of energy and why? All 3 types of metabolism involve 3 metabolic pathways central to the synthesis of the essential building blocks:

• Glycolysis (Embden-Meyerhoff Pathway)
  • 6 of 12 essential building blocks made
  • reducing power (NADH) generated
  • ATP made by substrate level phosphorylation (SLP)
    
• Tricarboxylic Acid Cycle (TCA cycle, Citric Acid Cycle)
  • 3 additional essential building blocks made
  • reducing power (NADH and FADH) generated
  • ATP made by SLP
    
• Oxidative Pentose Phosphate Pathway
  • 2 additional essential building blocks made
  • reducing power (NADPH) generated (used for biosynthesis and not ATP synthesis)

6. Types of metabolism carried by a chemoheterotrophic bacterium, E. coli used as an example. Why?

• Respiration (aerobic and anaerobic)-
  
  • A metabolic process in which an organic molecule serves as the primary electron donor (carbon source), and an inorganic molecule serves as the terminal electron acceptor.
    
    • if terminal electron acceptor is oxygen, process called aerobic respiration.
    • if terminal electron acceptor is an inorganic molecule other than oxygen, i.e., nitrate (NO₃), sulfate (SO₄^-2), or carbon dioxide (CO₂), process is called anaerobic respiration.
      
  • glycolysis, TCA cycle, and oxidative pentose phosphate pathway are required. Fig. 6.8 and 6.15
    
  • energy generation-
    
    • SLP- glycolysis and TCA cycle.
      
    • oxidative phosphorylation- by passage of the electrons/protons from NADH and/or FADH through the electron transport chain carriers, cell is able to generate proton motive force (chemiosmotic hypothesis, see below). Where are electrons/protons generated?
      
    • In aerobic respiration 43% of the available energy from glucose is "captured" in ATP (a total of 40 ATP's made for a net of 38 ATP's). Less energy made in anaerobic respiration than by aerobic respiration (why?), but still considerably more than by fermentation.
    • chemiosomotic hypothesis (Fig. 6.17): as protons/electrons are passed through a series of carriers that makeup the electron transport chain, in bacteria components are part of cytoplasmic membrane, protons are "pumped" to outside of cell, making cell outside environment more acid than inside or more electropositive on outside than inside. Both of these components makeup what is called an electrochemical gradient across membrane or proton motive force. Protons can re-enter cell via a transport mechanism or by ATPase. As protons enter cell via ATPase electrochemical energy is dissipated which is used to carry out oxidative phosphorylation (ADP plus inorganic phosphate, in cytosol, to make ATP).
      
• Fermentation- Fig. 6.20
  
  • a metabolic process in which an organic molecule serves as the primary electron donor (source of carbon), and the terminal electron acceptor (not same molecule!). How is NADH re-oxidized?
    
  • all ATP made by SLP (2.2% of energy available in a glucose molecule has been captured in a more usable form of chemical energy, ATP!). In what metabolic pathway is ATP made?
    
  • end-products of fermentation can be used to identify species.
    

8. Sewage treatment: the use of microorganisms that grow by respiration and fermentation are important in reducing the amount of organic material in sewage before it its discharged into a body of water like Puget Sound.

• What is BOD and is it better to have a body of water with a high or low BOD?
• What are the 3 stages of sewage treatment, and which one, and why, is the most important in lower BOD?

Learning Objectives:

• Define metabolism, and describe the fundamental differences between anabolism and catabolism.
• Understand what is meant by an oxidation-reduction reaction and know it's importance.
• Know the 3 general ways that ATP can be made by cells.
• Summarize what is accomplished when glucose is metabolized via the glycolytic pathway and the TCA cycle.
• Describe fermentation and know it's importance and/or significance.
• Compare and contrast aerobic and anaerobic respiration.
• How is proton motive force established, and used to make ATP.
• Metabolism of chemolithotrophic bacteria (Hydrogen bacteria). 
• Understand how sewage is treated by most large cities.

6/15/09