Problem Set #6

Modern Biology 03-121 Spring 98

Due Wed. 4/15

answers are in bold print

1. The following is a portion of the DNA sequence of a normal hemoglobin gene (assume the sequence is in-frame starting with the first three bases):

5'...GTGCACCTGACTCCTGAGGAG...3'

The following is a portion of the DNA sequence from a mutant hemoglobin gene:

5'...GTGCACCTGACTCCTGTGGAG...3'

a. This is an example of what type of mutation? (2.5 pts)

base substitution mutation/missense mutation

b. How would the polypeptide product of the normal gene differ from that of the mutant gene? (2.5 pts)

a leucine would be replaced by a histidine

2a. Diagram the lactose operon ofE. Coli in the absence of lactose. Label the following: repressor gene, promoter, operator, gene 1, gene 2, gene 3, repressor protein. Indicate what would happen to the repressor protein if lactose were present. Use the back of this sheet. (4 pts)

see your text

b. For E. coli to use lactose as an energy source, the sugar must be cleaved into the monosaccharides glucose and galactose by the enzyme B-galactosidase, which is encoded by one of the genes in the lactose operon. (1 pt)

3a. Why are restriction enzymes important to recombinant DNA technology? (3 pts)

Because restriction enzymes cut DNA molecules at specific base sequences, they allow for the controlled cutting of DNA. Some restriction enzymes produce DNA molecules with"sticky ends" which can base pair with the "sticky ends" of any other DNA molecule cut with the same restriction enzyme. Thus, when two molecules cut with the same restriction enzyme are mixed together in the presence of DNA ligase, a recombinant DNA molecule can be formed.

b. Give an example of a palindromic DNA sequence that could be cut by a restriction enzyme. (2 pts)

any palindromic sequence is acceptable, such as:

AATATT

TTATAA