Biology 12

248 MHR • Unit 3 Molecular Genetics

23.Provide evidence to support the conclusion

that DNA is, in fact, the genetic material.

24.As part of your research you isolate the DNA

from a particular strain of virus. Your analysis

indicates the following base composition:

(a)What can you conclude about the DNA of

this virus?

(b)What results would you expect to see if you

conducted the same analysis immediately

after the viral DNA had replicated?

25.Chargaff concluded that in any sample of DNA,

the amount of adenine would be equal to the

amount of thymine, and the amount of guanine

would be equal to the amount of cytosine.

Watson and Crick concluded that adenine

paired with thymine, and cytosine paired with

guanine. Explain how you think the structure

and function of DNA would change if cytosine

paired with adenine instead?

26.A particular species of bacteria can normally

exist on a minimal medium. In your research,

however, you find a mutant variety that will

only grow if the amino acid valine is added to

the medium. You know that the metabolic

base

concentration (%)

A

36

C

24

G

18

T

22

INQUIRY

(b)pyrimidine and purine

(c)DNA polymerase and DNA ligase

12.After one round of replication in a bacterial

colony, Meselson and Stahl’s analysis showed

one band of hybrid DNA. What is the most

useful interpretation they could draw from

this result?

(a)that DNA replication can be neither

conservative nor dispersive

(b)that the results are consistent with semi-

conservative replication

(c)that the results indicate either conservative

or semi-conservative replication

(d)that the results are not consistent with

conservative replication

13.If Meselson and Stahl continued their study

into a fourth generation of replication, what

result would they see?

14.Refer to Appendix 4 to review the cell life

cycle. Does DNA replication occur during

mitosis or meiosis, or both?

15.Arrange the following events in the order in

which they occur during the replication of a

single portion of a DNA molecule.

(a)primase synthesizes new RNA strand

(b)helicases cleave DNA

(c)30 nm array loosens

(d)ligase catalyzes formation of a phosphate

bond

(e)recognition of replication origin

(f )DNA polymerase adds nucleotides to a

fragment of DNA

16.Fill in the following table to show the

molecules and enzymes involved in DNA

replication.

17.A researcher combines in a solution all the

molecules required for DNA replication except

DNA ligase. What result would you expect to

see after a complete round of replication?

18.How does the base-pairing property of DNA

contribute to the proofreading function of DNA

polymerase?

19.Compare the process of replication in

prokaryotic and eukaryotic cells. How do

differences in the structure of DNA contribute

to differences in replication?

20.In what ways is the one gene-one enzyme

definition of a gene inaccurate?

21.During the process of cell division in a human

cell, the chromosomes are visible under a

microscope as short, thick strands. Describe

how a single molecule of DNA is organized

within one of these chromosomes.

22.A gene coding for the same enzyme is found in

both earthworms and rats. Which gene is likely

to have a greater total length? Explain.

Molecule or

enzyme Function

Involved in leading

strand or lagging strand

synthesis, or both

primer

DNA ligase

DNA polymerase

Okazaki fragments

helicase