DNA

1.   DNA replication is said to be semiconservative because

A.  synthesis can proceed uninterrupted (as a leading strand) in only one direction.

B.  each new DNA molecule contains one preexisting strand and one new strand.

C.  after each round of DNA replication, the original DNA double helix is still intact.

D.  the original base sequence is conserved in the daughter DNA molecules.

2.   Name the scientists who:

A.  showed that different species possess DNA with different ratios of nitrogenous bases: _____________________________.

B.  showed that bacteria can acquire new genetic information from their surroundings: _______________________;  and who later showed that that genetic information appeared to be nucleic acids: _____________________.

C.  generated the first high quality X-ray diffraction images of DNA: ________________________.

D.  showed that viruses pass DNA not protein to cells that they infect: ________________________.

E.   elucidated the three dimensional structure of the DNA molecule: ________________________.

F.   showed that DNA replication is semiconservative: ____________________________.

3.   In the experiments carried out by Hershey-Chase, bacteriophage viruses were labeled with either radioactive phosphorous (³²P) or sulfur (³⁵S).

A.    Which one of these radionucleotides labels protein?  Why?  _______________________

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B.     Which one of these radionucleotides labels nucleic acids?  Why?  ___________________

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C.     What result would have been obtained if instead the bacteriophages were labeled with radioactive nitrogen (¹³N)?  Explain.  _________________________________________

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4.   Complete the following table

Species	Percentage of each base
	Adenine	Cytosine	Thymine	Guanine
A	23	27	23
B	18	32
C	20		20
D				24

      Who discovered the relationships shown in the above table? _________________________

5.   Frederick Griffith carried out a series of experiments using pathogenic (encapsulated) and non-pathogenic (non-encapsulated) strains of the bacterium Streptococcus pneumoniae.  The most important finding of his experiments was that:

A.    Information about the traits of a cell could be passed between organisms.

B.     DNA appeared to carry the genetic information of the cell.

C.     The capsule of this species of bacteria is necessary for it to cause disease.

D.    Mutation in DNA can alter the traits of a cell.

6.   The experiments of T. Oswald Avery extended the findings of Griffith by demonstrating that ____ (select answer from above).

7.   Suppose you replicated the experiment of Meselson and Stahl, growing the cells on media containing ¹⁵N, and then transferring them to media containing ¹⁴N.  Which generation of cell division after being transferred to the ¹⁴N media would yield DNA that contained 75% light density DNA and 25% intermediate density DNA?

A.    F₁                           D. F₄

B.     F₂                           E. F₅

C.     F₃

Explain your answer.

8. ‘Wobble base pairing’ will occur for which one of the following pairs codons? 

            A. AUG and UGG                 C. GGA and GGC

            B. AAA and UUU                 D. UAG and UGA

9. As a new DNA strand is being synthesized, it elongates in both directions. Which one of these processes:

1) elongation of the leading strand, or

2) creation of new lagging strands

contributes to elongation of the new strand on the:

A.    3’ end?   ____

B.     5’ end?   ____

10. A. Which one of the following answers correctly shows the orientation of strands in the DNA double helix?

            1.   3’ - ATGCATGCATGCATGC – 5’        4.   3’ - ATGCATGCATGCATGC – 5’

                  3’ - ATGCTAGCATGCATGC – 5’              5’ - TACGTACGTACGTACG – 3’

            2.   3’ - ATGCATGCATGCATGC – 5’        5.   3’ - ATGCATGCATGCATGC – 5’

                  5’ - ATGCTAGCATGCATGC – 3’              5’ - CGTACGTACGTACGTA – 3’

            3.   3’ - ATGCATGCATGCATGC – 5’

                  3’ - TACGTACGTACGTACG – 5’

      B. In #3 above, circle an example of an ‘AT’ base-pair and an example of a ‘GC’ base-pair.

      C. Write in the base sequence that is complementary to this:  

                           3’ – A A G C T C G A T T C G – 5’

      Now explain why each of these statements is false:

            1. “The DNA sequence in the two strands of the double helix are identical but run in the opposite directions.”

            2. “The DNA sequence in the two strands of the double helix are independent of each other.”

11. Replication of DNA requires a primer to initiate DNA synthesis because DNA polymerase can add new nucleotides:

A. only to an RNA chain.                      C. only in the 5¢-to-3¢ direction.

B. only to a base-paired nucleotide.      D. only in short fragments.

12. The line below represents a single DNA strand and the position of a replication origin. 

            A.  Below the strand, show the arrangement of the complementary leading strand and two

                  lagging strands (as simple lines and arrows) as they would be arranged around the

                  replication origin.

            B.  Label the 5’ and 3’ ends.

            C.  For the new strands, indicate the expected positions of the RNA primer, DNA strand and

                  DNA polymerase III.

                                                                   Repl origin

            3’______________________________ò___________________________5’ template

                    | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |

13. During the synthesis of each new Okazaki fragment, the following enzymes operate sequentially. 

A.  Next to each protein, add a number to indicate the order in which the proteins function during the synthesis of a new stretch of DNA.

____ DNA ligase - _____________________________________________________

____ DNA exonuclease/polymerase – I - ___________________________________

____ DNA helicase - ___________________________________________________

____ DNA polymerase – III - ____________________________________________

____ RNA primase - ___________________________________________________

B.  Briefly describe the function of each protein.

14. A mutation would be best described as

A.  any change to a cell that affects its function.

B.  a change in the shape of a protein.

C.  a change in the base sequence of DNA.

15. A thymine dimer would be best described as

A.  a base substitution

B.  a base deletion

C.  chromosome aberration

D.  a chemical modification

16. Excision repair of DNA requires both the action of a DNA endonuclease, ligase, and DNA polymerase.  Describe the function of each enzyme during this process.

      DNA endonuclease:

      DNA ligase:

      DNA polymerase:

17. Proof-reading during DNA replication refers to:

A. removal of the RNA primer before connecting Okazaki fragments.

B. pairing of A with T and G with C by DNA polymerase.

C. removal of thymine dimers by excision repair.

D. checking for correct base pairing by DNA polymerase.

18. A cell is said to be totipotent if:

A. it could potentially differentiate into any cell type.

B. it can divide by mitosis to yield an identical cell.

C. it is eukaryotic and contains a nucleus.

D. it has been cloned from another cell.

19. The relationship between the sequences of bases in DNA and amino acids in protein would be best stated as:

A.  The sequence of nucleotides in DNA is determined by the amino acid sequence of DNA polymerase.

B.  The sequence of nucleotides in a DNA is determined by the amino acids in proteins.

C.  The sequence of amino acids is determined by the relative percentages of A, T, G and C in the DNA.

D.  The sequence of amino acids is determined by the sequence of nucleotides in a gene.

20. Watson and Crick, although they did not perform any specific laboratory-based experiments themselves were awarded the Nobel Prize for elucidating the structure of the DNA double helix.

            A. Whose X-ray diffraction data helped them to solve the structure?  ___________________

            B. What are three important features of the structure of DNA that they figured out?