Study Guide 6
Last revised: Wednesday, February 6, 2002
Topic: Energetics and Enzymes
Chapter 6.

  1. Terms. Be able to recognize and correctly apply the following terms:
    Enzyme
    Substrate
    Induced fit
    Actve site

  2. What is meant by the term "metabolism"? How do catabolic and anabolic metabolism differ?
  3. State the 1st and 2nd laws of thermodynamics. How does each apply to biological systems?
  4. How is free energy defined? Why is free energy rather than heat energy used to measure changes in chemical reactions?
  5. Informational note: the free energy change, G, of any chemical reaction will vary depending on concentrations of the reactants and temperature. Biochemists often refer to the “standard free energy change” of a reaction, Go’, which is a constant for any given reaction, and which can be used to predict something about the amount of energy liberated (or taken up) by the reaction. For example, the Go’ for ATP hydrolysis is –7.3 kcal/mole. However, in actual cells, the amount of energy liberated is somewhat higher (because concentrations are different from standard conditions), around –10 to –12 kcal/mole.
  6. One use of the G notation is in predicting direction and amount of energy involved. All spontaneously occurring reactions have negative G values. The larger the value, the more energy is released. A reaction with Go’ = –1.5 kcal/mole will release a little energy, but not enough to do useful cell work. A reaction with a Go’ = –688 kcal/mole will release lots of energy. Such reactions are the primary source of metabolic energy for most cells.
  7. What is an enzyme? What do enzymes do? Pay special attention to Fig. 6.9 and 6.10.
  8. Do enzymes affect the Go’ of a reaction (e.g., can an enzyme make a reaction that would normally have a + value into a spontaneous reactions with a – value?)
  9. How big is the catalytic site of an enzyme, relative to the number of amino acids in an enzyme? (See Fig. 6.11 if you're stumped). What is meant by “induced fit”?
  10. How and why do the following factors affect enzyme activity: temperature, pH, salt, denaturation, inhibitors, cofactors.
  11. What is an allosteric enzyme? How does it differ from a normal enzyme? Which reaction in a pathway A –(E1)–> B–(E2)–> C–(E3)–> D –(E4)–> E would you expect to be an allosteric enzyme? [Note: the notation employed here means that E1 is the enzyme catalyzing the reaction A––>B, etc.] Why?


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