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2012-09-08 22:57:19
Enzymes biochemistry NSU

Introduction to Enzymes
Show Answers:

  1. What is an enzyme?
    a protein catalyst for specific biochemical reactions
  2. What does an enzyme affect?
    they speed up reactions by lowering the activation energy of a reaction. Gibbs free energy is altered.
  3. What does an enzyme not affect?
    Keq and deltaG are not affected by enzymes
  4. Name 2 models used to describe enzyme specificty and/or catalytic activity
    • The lock and key model
    • The induced fit model
  5. What is a prosthetic group?
    • Small non-protein organic molecule that tightly binds to the enzyme's active site.
    • When the prosthetic group is attached, an apoenzyme becomes a holoenzyme
  6. Name the 6 classes of enzymes
    • 1. oxidoreductases
    • 2. transferases
    • 3. hydrolases
    • 4. lyases
    • 5. isomerases
    • 6. ligases
  7. What is the michaelis menton equation and what do the terms mean?
    • V=Vmax[S]/(Km+[S])
    • Km = constant value for specific substrate, Michalis constant
    • Vmax = maximum velocity of rxn
    • [S] = substrate reaction
    • V = velocity of reaction
  8. In an Michaelis-Menten plot, where is Vmax and how do you find Km?
    • Vmax is found when [S] is very high. Where all the enzyme is converted to the ES complex. 
    • Km is determined by finding [S] when V = 1/2 Vmax
  9. A lineweaver-burk plot is also called a _________ ______ plot.
    double-reciprocal plot
  10. What are the vertical and horizontal intercepts of the lineweaver-burk plot?
    • vertical = 1/Vmax
    • horizontal = -[1/Km]
  11. What is plotted in a Michaelis-Menten plot?
    [1/V] vs. 1/[S]
  12. What are the advantages of the Eadie-Hofstee plot?
    It will give more evenly spaced data points, not clustered like the LB plot
  13. What distinguishes a competitor inhibitor from the rest?
    • They bind directly to the active site.
    • They can be overcome by increasing [S]
  14. What does the inhibitor bind with for competitive, non competitive, and uncompetitive inhibition?
    • competitive = active site
    • non competitive = react w/ enzyme to reduce its effectiveness to bind with substrate
    • uncompetitive = bind with the ES complex (irreversible) to form the ESI complex
  15. What does the sigmoid V vs [S] plot as well as a curved lineweaver-burk plot indicate?
    • indicates allosteric enzyme reaction
    • positive cooperativity of the enzyme
  16. On the Lineweaver-Burk plots are the vertical and horizontal intercepts the same or different for a.) competitive, b.) non-competitive and c.) uncompetitively inhibited reactions?
    • On Linewaver-Burk plots:
    • A) Competitive inhibitors show a steeper slope than uninhibited reactions, but have the same 1/Vmax point.
    • B) Noncompetitive inhibitors show a steeper slope, but have the same -1/Km point.
    • C) Uncompetitive Inhibitors show the same slope, but shifts the curve left, showing a greater -1/Km value.