Part A. Definitions (1 pt each)
1. Active site-

2. ____________________________ is the "hill" which must be gotten over to convert substrate to product.

3. X-ray diffraction-

4. ____________________________ is an enzyme-prosthetic group complex.

5. K_0.5-

6. ________________________ is an organic molecule required in the diet as a precursor to coenzymes.

7. Substrate-

8. Transition state

9. ____________________________ is an enzyme synthesized as a longer than usual, inactive form.

10. Binding energy-

11. Homotropic feedback inhibition-

12. Enzyme-

13. K_cat-

14. ____________________________ is the fastest rate at which an enzyme can catalyze its reaction.

Part B. Concepts and applications thereof
1. Explain the differences between the lock and key model and the induced fit model of enzyme specificity. (5 points)

2. Explain why enzymes display a pH optimum. (5 points)

3. Write the Michaelis-Menton equation and define what each of the terms mean. (8 points)

4. Below is a hypothetical substrate/product pair. Diagram what amino acids might be useful in the active site and what their approximate layout would be (two-dimensionally). Also discuss ( a sentence or two) what role each amino acid would play. (10 points)

5. What is (are) the difference(s) between a cofactor and a coenzyme? (5 points)

6. From the following data, determine the Km and Vmax of the enzyme, and the type of inhibition. (10 points)

                                                Inhibitor concentration
                                                 0 mM              1.0 mM
Tube        Substrate, mM             velocity, µM/min
   1            0.05                         0.33                 0.14
   2            0.10                         0.50                 0.25
   3            0.20                         0.67                 0.40
   4            0.40                         0.80                 0.57
   5            0.50                         0.83                 0.63
 

7. Assume the following flow diagram refers to an amino acid biosynthetic pathway, where the capital letters indicate metabolic intermediates and the numbers indicate enzymes. Suggest a scheme by which this pathway might be allosterically regulated (which enzymes would be inhibited by which intermediate). (5 points)

8. Write a rate expression for the following reaction. (5 points)

9. Explain the following observation: An enzyme which binds oxaloacetate (CH₃CH₂COCO₂^-) at the normal intracellular pH of 7.4 does not bind the substrate efficiently at pH 9.5. (5 points)

10. Explain the mechanisms of competitive, noncompetitive and uncompetitive inhibition. (10 points)

11. What coenzyme would you expect to be used in the following reaction? (Give the name.) If not coenzyme is needed, indicate as such. Also indicate the class of enzyme involved (name and E.C. number). (18 points)