Study Questions for Exam 2

Study Question Set 9
Enzymes and Enzyme Kinetics

Lehninger Chapter 7 Question 1

 

Chapter 8

Questions

3, 7b, 8, 9(use graphical analysis)

       

Osgood

Chapter 8

Topics

1, 3, 4, 19, 20, 23 - 28, 33, 35

   

Facts

1, 2, 3, 8, 9 - 13, 19, 20, 21 (a, c-g), 22
(Q8: Also indicate which major types seen for 2-substrate reactions are missing and plot them.)

   

Applying

1, 2.


Additional Questions

  1. Explain the significance of VMAX, KM, kon (k1 in Lehninger), koff (k-1 in Lehninger), kr (k2 in Lehninger), and [ES].
  2. What type of inhibitor should be useful in trying to identify what features of a substrate are important for binding the substrate to the active site of an enzyme catalyzing a single-substrate reaction? Why? How would one use the inhibitor to obtain this information?
  3. An enzyme has a Vmax of 150 micromoles product formed per minute by a mg of enzyme. The KM for the major substrate of the enzyme is 1.5 mM.
    • What is the initial reaction rate (vo) when the [S] is 0.5 mM?
    • What is the initial reaction rate (vo) when the [S] is 3.0 mM?
    • What is the initial reaction rate (vo) when the [S] is 15.0 mM?
  4. Indicate whether each of the following is true or false. If the statement is false, explain why.
    • The rate of an enzyme-catalyzed reaction is a linear function of the substrate concentration.
    • An enzyme-catalyzed reaction velocity reaches Vmax when the
      substrate concentration is equal to 2 x Km.
    • The Michaelis constant (Km) of an enzyme identifies the substrate concentration at which 50% of the enzyme active sites, on average, have substrate bound to them.
  5. Refer to question 11 in Chapter 8 of Lehninger.   Indicate which curve repressents competitive inhibition Explain.   What types of inhibition are represented by the other two curves?
  6. Distinguish (generally) between bisubstrate enzyme-catalyzed reactions having a "double-displacement" mechanism and bisubstrate enzyme-catalyzed reactions having a "sequential" mechanism.
  7. Distinguish (generally) between ordered sequential bisubstrate reactions and random sequential bisubstrate reactions.   Which is more complex to describe kinetically?    Why?
  8. Which type of sequential bisubstrate enzyme-catalyzed reaction is likely to exhibit "uncompetitive inhibition" when one of its products is tested as an inhibitor of the reaction?    Explain.
  9. Under what conditions can a bisubstrate enzyme-catalyzed reaction with a double-displacement mechanism be treated kinetically as if it is a single-substrate reaction?    (I.e., under what conditions does its Michaelis-Menten equation approximate that for a single-substrate reaction?)
  10. Go to the Interactive Biochemistry web page by Professor Charles M. Grisham and Mr. Edward K. O'Neil at the University of Virginia at "http://cti.itc.Virginia.EDU/~cmg". Try the tutorials on Enzyme Kinetics.
  11. Here is a tutorial from the Biochemistry Course at the University of Arizona http://www.biology.arizona.edu/biochemistry/problem_sets/energy_enzymes_catalysis/01Q.html. This tutorial has study questions with tutorials linked to answers. It also includes a question on allosteric proteins, which we will cover after we discuss enzyme mechanisms.

Selected Answers

  1. See Lehninger.
  2. Competitive.   Binds substrate binding site.   If there is no easy way to measure normal product, use radioactive substrate and quantify reaction from radioactive product formed.  Determine Vmax and KM in the absence of inhibitor and at one or more inhibitor concentrations.
  3.  
    • When the [S] is 0.5 mM, vo = 37.5 micromoles per minute per mg protein.
    • When the [S] is 3.0 mM, vo = 100 micromoles per minute per mg protein.
    • When the [S] is 15.0 mM, vo = 136.4 micromoles per minute per mg protein.
  4. Statements (a) and (b) are false.
  5. See page S-54 in Osgood for an explanation f part of the answer. A represents competitive inhibition. B represents non-competitive inhibition. C frepresents some sosrt of activator that causes an apparent decrease in KM, probably by the affinity of the enzyme for its substrate as a consequence of binding at some site other than the active site.
  6. See lecture material on bisubstrate reactions.
  7. See lecture material on bisubstrate reactions.   The Random Sequential Reaction kinetics are much more complex to analyze than the Ordered Sequential Reaction -- because substrate binding order is random!
  8. See lecture material on bisubstrate reactions - and think!
  9. The Michaelis Menten equation for a bisubstrate reaqction with a double displacement mechanism reduces to the equation for a single substrate reaction when the concentration of the second substrate is extremely large relative to the binding affinity for that substrate, as is the case when that substrate is water.


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