1. The following statements about restriction endonucleases 

     is true EXCEPT:

a. they cut DNA at defined sequences.

b. they are natural products of bacteria.

c. they cut only single-stranded DNA molecules.

d. they are so named because they restrict the growth of 

    bacteriophage.

e. they cut sugar-phosphate backbones of the DNA without 

    damaging the nitrogenous bases. 

AnswerAnswer: c

Restriction endonucleases are produced by bacteria 

and cut double stranded DNA. The cut occurs at 

specific base sequences.

..

a. the presence of uracil in RNA in place of thymidine in DNA.

b. the presence of 3' deoxyribose in DNA, ribose in RNA.

c. the presence of guanine in DNA in place of cytosine in DNA.

d. the occurrence of base pairing in DNA but not RNA.

e. the presence of 5' phosphate in DNA but not RNA.

AnswerAnswer: a

The sugar in DNA is 2' deoxyribose, not 3'. Base 

pairing can occur in both DNA and RNA; in RNA it 

results in secondary structures such as hairpins. 

Both RNA and DNA have a 5' phosphate 

..

3. The mutation that is most likely to lead to premature

     termination of translation is:

a. deletion of three bases from DNA.

b. insertion of single base into an extron of a DNA.

c. insertion of single base into an intron of a DNA.

d. single base change in a promoter.

e. deletion of an entire gene.

AnswerAnswer: b

A single base insertion in the extron (the coding part of a 

DNA; the uncoding part of a DNA is called intron) would 

cause a frameshift and usually leads to premature 

termination of translation. Deletion of three bases would 

delete an entire codon. Deletion of the entire gene would 

lead to complete lack of translation, and a mutation within 

the promoter could alter gene regulation.

.

4. The northern blot is a technique used in molecular biology 

     research to study :

a. single-stranded DNA.

b. double-stranded DNA.

c. RNA.

d. mitochondrial DNA.

e. ribosomes.

AnswerAnswer: c

Southern blot studies DNA.

.

5. The chromosomes line up at the equator of the cell

     at which phase of the mitosis:

a. interphase

b. prophase

c. metaphase

d. anaphase

e. telephase

AnswerAnswer: c

The chromosomes prepare to divide at the interphase; 

condense during prophase; line up on the equator of 

the cell in metaphase, and begin to separate during 

anaphase. Telophase is phase when chromosomes have 

segregated to the poles and the nuclear membrane 

reforms.