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					Homework 4. Bio 201.

For questions 1-4 select the correct answer.
1. The 20 different amino acids are distinguished by:
a. location of carboxyl groups
b. location of amino groups
c. “side chain” or “R group” composition
d. ability to form peptide bonds
                                                                    (0.5 point)

2. What type of interaction is directly responsible for the formation of secondary
   structure in a polypeptide?
a. peptide bonds between adjacent amino acids
b. peptide bonds between non-adjacent amino acids
c. hydrogen bonds between side chains of amino acids
d. hydrogen bonds between sections of the polypeptide backbone.
                                                                    (0.5 points)

3.   All proteins
a.   are enzymes
b.   consist of one or more polypeptide chains
c.   are amino acids
d.   have quaternary structures
                                                                    (0.5 point)

4.   Which of the following statements about condensation reactions is NOT true.
a.   Protein synthesis results from them
b.   Polysaccharide synthesis results from them.
c.   Different condensation reactions produce different kinds of macromolecules.
d.   They consume water as a reactant.
                                                                    (0.5 point)

5. Look at fig. 3.3 in your textbook (fig 3.5 in the 2nd edition). Consider the amino acids
   histidine, glutamic acid, threonine, and leucine. Suppose all of these were part of a
   protein. Which of them would most likely?
a. Interact well with lipid?
b. Be folded up deep in the center of a protein that is generally in an aqueous
   environment (surrounded by water)?
c. Which would interact best with the R-group of the amino acid Aspartic acid?
d. Which (more than one answer) could interact well with water?
                                                                      (2 points)
6. Bacteria that live in extremely cold water are called psychrophiles. Do you think the
   cell membranes of these bacteria would have especially high levels of saturated or
   unsaturated fatty acids in their phospholipids? Explain your answer.
                                                                    (1 point)

7. What properties allow phospholipids to form membrane bilayers? Why can’t a fatty
   acid do this?
                                                               (1 point)

8. Draw a short peptide composed of three different amino acids. Label the C terminus
   and N terminus and indicate the position of the peptide bonds. Place partial charges
   on the terminal groups. Which of your three amino acids would be (a) most and (b)
   least likely to form hydrogen bonds with water molecules.
                                                                   (3 points)

9. Fill in the missing words.
a. “__________________ structure is the result of two or more protein subunits
   assembling to form a larger, biologically active protein complex.”
b. “__________________ structure is achieved when a protein folds into a compact,
   three dimensional shape stabilized by interactions between side chain R groups of
   amino acids.”
                                                                   (1 point)

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