Problem 87
Which of the following polymers would be stronger or more rigid? Explain your choices. a. The copolymer of ethylene glycol and terephthalic acid or the copolymer of \(1,2\) -diaminoethane and terephthalic acid \(\left(1,2 \text { -diaminoethane }=\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\right)\) b. The polymer of \(\mathrm{HO}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{CO}_{2} \mathrm{H}\) or that of c. Polyacetylene or polyethylene (The monomer in polyacetylene is ethyne.)
Problem 88
Poly(lauryl methacrylate) is used as an additive in motor oils to counter the loss of viscosity at high temperature. The structure is The long hydrocarbon chain of poly(lauryl methacrylate) makes the polymer soluble in oil (a mixture of hydrocarbons with mostly 12 or more carbon atoms). At low temperatures the polymer is coiled into balls. At higher temperatures the balls uncoil and the polymer exists as long chains. Explain how this helps control the viscosity of oil.
Problem 90
When pure crystalline amino acids are heated, decomposition generally occurs before the solid melts. Account for this observation. (Hint: Crystalline amino acids exist as \(\mathrm{H}_{3} \mathrm{NCRHCOO}^{-},\) called zwitterions.)
Problem 91
Aspartame, the artificial sweetener marketed under the name NutraSweet, is a methyl ester of a dipeptide: a. What two amino acids are used to prepare aspartame? b. There is concern that methanol may be produced by the decomposition of aspartame. From what portion of the molecule can methanol be produced? Write an equation for this reaction.
Problem 94
Draw the structures of the tripeptides gly–ala–ser and ser–ala–gly. How many other tripeptides are possible using these three amino acids?
Problem 95
Write the sequence of all possible tetrapeptides composed of the following amino acids. a. two phenylalanines and two glycines b. two phenylalanines, glycine, and alanine
Problem 96
How many different pentapeptides can be formed using five different amino acids?
Problem 97
In general terms, what does the secondary structure of a protein represent? How is the secondary structure of a protein related to its function?
Problem 98
In general terms, what does the tertiary structure of a protein represent? Distinguish between the secondary and tertiary structures of a protein.
Problem 100
What types of interactions can occur between the side chains of the following amino acids that would help maintain the tertiary structure of a protein? $$ \begin{array}{ll}{\text { a. cysteine and cysteine }} & {\text { c. glutamic acid and lysine }} \\ {\text { b. glutamine and serine }} & {\text { d. proline and leucine }}\end{array} $$
