Question 10.17

The introduction to this chapter, about the sequencing of 4000-year-old DNA, emphasizes DNA’s extreme stability. What aspects of DNA’s structure contribute to the stability of the molecule? Why is RNA less stable than DNA?

Question 10.18

Match the researchers (a–j) with the discoveries listed.

• a. Kossel
• b. Fraenkel-Conrat
• c. Watson and Crick
• d. Levene
• e. Miescher
• f. Hershey and Chase
• g. Avery, MacLeod, and McCarty
• h. Griffith
• i. Franklin and Wilkins
• j. Chargaff

• ______ Took X-ray diffraction pictures used in constructing the structure of DNA.
• ______ Determined that DNA contains nitrogenous bases.
• ______ Identified DNA as the genetic material in bacteriophage.
• ______ Discovered regularity in the ratios of different bases in DNA.
• ______ Determined that DNA is responsible for transformation in bacteria.
• ______ Worked out the helical structure of DNA by building models.
• ______ Discovered that DNA consists of repeating nucleotides.
• ______ Determined that DNA is acidic and high in phosphorous.
• ______ Conducted experiments showing that RNA can serve as the genetic material in some viruses.
• ______ Demonstrated that heat-killed material from bacteria can genetically transform live bacteria.

Question 10.19

A student mixes some heat-killed type IIS Streptococcus pneumoniae bacteria with live type IIR bacteria and injects the mixture into a mouse. The mouse develops pneumonia and dies. The student recovers some type IIS bacteria from the dead mouse. If this is the only experiment conducted by the student, has the student demonstrated that transformation has taken place? What other explanations might explain the presence of the type IIS bacteria in the dead mouse?

Question 10.20

Predict what would happen if Griffith had mixed some heat-killed type IIIS bacteria and some heat-killed type IIR bacteria and injected these into a mouse. Would the mouse have contracted pneumonia and died? Explain why or why not.

Question 10.21

Explain how heat-killed type IIIS bacteria in Griffith’s experiment genetically altered the live type IIR bacteria. (Hint: See the discussion of transformation in Chapter 9.)

Question 10.22

What results would you expect if the Hershey and Chase experiment were conducted on tobacco mosaic virus?

Question 10.23

Which of the processes of information transfer illustrated in Figure 10.16 are required for the T2 phage reproduction illustrated in Figure 10.4?

Question 10.24

Imagine that you are a student in Alfred Hershey and Martha Chase’s lab in the late 1940s. You are given five test tubes containing E. coli bacteria that were infected with T2 bacteriophage that have been labeled with either ³²P or ³⁵S. Unfortunately, you forgot to mark the tubes and are now uncertain about which were labeled with ³²P and which with ³⁵S. You place the contents of each tube in a blender and turn it on for a few seconds to shear off the protein coats. You then centrifuge the contents to separate the protein coats and the cells. You check for the presence of radioactivity and obtain the following results. Which tubes contained E. coli infected with ³²P-labeled phage? Explain your answer.

Question 10.25

Figure 10.8 illustrates Fraenkel-Conrat and Singer’s experiment on the genetic material of TMV. What results would you expect in this experiment if protein carried the genetic information of TMV instead of RNA?

Question 10.26

DNA molecules of different sizes are often separated with the use of a technique called electrophoresis (see Chapter 19). With this technique, DNA molecules are placed in a gel, an electrical current is applied to the gel, and the DNA molecules migrate toward the positive (+) pole of the current. What aspect of its structure causes a DNA molecule to migrate toward the positive pole?

Question 10.27

Each nucleotide pair of a DNA double helix weighs about 1 × 10⁻²¹ g. The human body contains approximately 0.5 g of DNA. How many nucleotide pairs of DNA are in the human body? If you assume that all the DNA in human cells is in the B-DNA form, how far would the DNA reach if stretched end to end?

Question 10.28

One nucleotide strand of DNA molecule has the base sequence illustrated below.

5′-ATTGCTACGG-3′

Give the base sequence and label the 5′ and 3′ ends of the complementary DNA nucleotide strand.

Question 10.29

Erwin Chargaff collected data on the proportions of nucleotide bases from the DNA of a variety of different organisms and tissues (E. Chargaff, in The Nucleic Acids: Chemistry and Biology, vol. 1, E. Chargaff and J. N. Davidson, Eds. New York: Academic Press, 1955). The following data are from the DNA of several organisms analyzed by Chargaff.

Erwin Chargaff.

[Horst Tappe/Getty Images.]

• a. For each organism, compute the ratio of (A + G)/(T + C) and the ratio of (A + T)/(C + G).
• b. Are these ratios constant or do they vary among the organisms? Explain why.
• c. Is the (A + G)/(T + C) ratio different for the sperm samples? Would you expect it to be? Why or why not?

Question 10.30

Boris Magasanik collected data on the amounts of the bases of RNA isolated from a number of sources, expressed relative to a value of 10 for adenine (B. Magasanik, in The Nucleic Acids: Chemistry and Biology, vol. 1, E. Chargaff and J. N. Davidson, Eds. New York: Academic Press, 1955).

• a. For each organism, compute the ratio of (A + G)/(U + C).
• b. How do these ratios compare with the (A + G)/(T + C) ratio found in DNA (see Problem 29)? Explain.

Question 10.31

Which of the following relations or ratios would be true for a double-stranded DNA molecule?

• a. A + T = G + C
• b. A + T = T + C
• c. A + C = G + T
• d.
• e.
• f.
• g.
• h.

Question 10.32

If a double-stranded DNA molecule is 15% thymine, what are the percentages of all the other bases?

Question 10.33

Suppose that each of the bases in DNA were capable of pairing with any other base. What effect would this capability have on DNA’s capacity to serve as the source of genetic information?

Question 10.34

Heinz Shuster collected the following data on the base composition of ribgrass virus (H. Shuster, in The Nucleic Acids: Chemistry and Biology, vol. 3, E. Chargaff and J. N. Davidson, Eds. New York: Academic Press, 1955). On the basis of this information, is the hereditary information of the ribgrass virus RNA or DNA? Is it likely to be single stranded or double stranded?

Ribgrass mosaic virus.[Jena Library of Biological Macromolecules.]

297

Question 10.35

The relative amounts of each nucleotide base are tabulated here for four different viruses. For each virus listed in the following table, indicate whether its genetic material is DNA or RNA and whether it is single stranded or double stranded. Explain your reasoning.

Question 10.36

A B-DNA molecule has 1 million nucleotide pairs. How many complete turns are there in this molecule?

Question 10.37

For entertainment on a Friday night, a genetics professor proposed that his children diagram a polynucleotide strand of DNA. Having learned about DNA in preschool, his 5-year-old daughter was able to draw a polynucleotide strand, but she made a few mistakes. The daughter’s diagram (represented here) contained at least 10 mistakes.

• a. Make a list of all the mistakes in the structure of this DNA polynucleotide strand.
• b. Draw the correct structure for the polynucleotide strand.

Question 10.38

Chapter 1 considered the theory of the inheritance of acquired characteristics and noted that this theory is no longer accepted. Is the central dogma consistent with the theory of the inheritance of acquired characteristics? Why or why not?

Question 10.39

Write a sequence of bases in an RNA molecule that will produce a hairpin structure.

Question 10.40

Write a sequence of nucleotides on a strand of DNA that will form a hairpin structure.