CH234 Chapter 19 Homework: Due Thursday, April 9, 2PM
1. What are the differences between the “lock and key” model and the “induced fit” model of enzyme action. Which one is more likely to be correct? Explain why.
2. Enzymes are large molecules, while the active site is a relatively small portion of the whole molecule. What is the function of the rest of the structure of the enzyme?
3. Acetylcholinesterase contains over 600 amino acids. The active site amino acids in acetylchlolinesterase are Ser 200, His 440 (which functions as both the acidic and basic groups in my PowerPoint), and Glu 327. How can these amino acids be so far away from each other, and still be close enough to form the active site?
4. Draw an arrow-pushing mechanism to show how ACHE catalyzes the hydrolysis of the following ester. You will need to draw the active site, and show how bonds are broken and formed. You can draw it out step by step, using eight steps like I did in the PowerPoint, or in two steps, like I showed on the board.
5. What general effect do you think each of the following changes would have on the rate of an enzyme-catalyzed reaction for an enzyme that has its maximum activity at 30ºC? Briefly explain your reasoning.
a. Changing the temperature to 20ºC.
b. Adding a concentrated solution of sodium chloride.
c. Adding an oxidizing agent, such as hydrogen peroxide (H2O2).
d. Doubling the concentration of enzyme’s substrate.
6. Chymotrypsin is an enzyme that hydrolyses only certain amide bonds in proteins or peptides. Specifically, it cleaves the amide bonds on the carboxyl side (the right side) of amino acids with aromatic rings in their side-chains. Predict the fragments formed when the following peptide is treated with chymotrypsin.
Val-Glu-Phe-Tyr-Ser-Trp-Thr-Val
Hint: Use the table of amino-acids on page 549. Assume that any rings on the side chains of the amino acids are aromatic.