Exam 2 CH 130

May 23, 1996

There are three pages and twelve questions on this exam. Be sure you have them all.

1. Describe or define precisely, providing an example

How a ketone and an aldehyde differ in structure

Optical isomers (enantiomers)

The hydrolysis of an ester

2. What is meant by the primary, secondary, and tertiary structure of a protein? Provide an example for each.

3. Draw three (3) esters with the formula C₅H₁₀O₂. Give the IUPAC name of ONE of them.

4. The isoelectric point of serine (G = -CH₂OH) is 5.7. Draw the predominant form(s) of the molecule in water of pH 3.0, in pH 5.7, and in pH 8.0.

5. Why did you need to perform "standardization" titrations before you analyzed commercial vitamin-C tablets?

6.

A.) Common amines react readily with HCl. Describe the reaction, showing a typical product.

B.) Predict whether this product would be more or less soluble in water than the unreacted amine, and briefly justify your answer.

7. Comment upon the accuracy of the statement, "Dyes which dye one type of cloth will dye all types of cloth well, and dyes which work poorly on one type of cloth will work poorly with all types of cloth." What evidence do you have to back up your comment?

8.

A.) Nylon can be produced by reacting HOOC-(CH₂)₄-COOH with H₂N-(CH₂)₆-NH₂. Describe this reaction, and show the general structure of Nylon.

B.) Nylon exhibits unusual mechanical strength. What structural features of the compound lead to this property?

9. Insulin is a globular protein. Why must diabetic patients receive insulin subcutaneously by injection rather than by swallowing pills?

10. The "R group" of leucine is -CH₂CH(CH₃)₂. Draw the structure of leucine and circle any chiral carbons.

11. What interaction is responsible for the coil stabilization in an helix? Describe with a diagram how the helix is stabilized.

12.

A.) Draw the actual molecular structure (not an abbreviation) of a tripeptide involving three different specific amino acids. Circle the "side groups," indicate the peptide links, and name the tripeptide.

B.) Using the three-letter abbreviations for the amino acids in this tripeptide, list all the possible structural isomers of this tripeptide.

C.) List three distinctly different ways that living systems use proteins.