17.The introduction to this chapter, which describes 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?

18.Match the scientists with the discoveries listed.

— Took X-ray diffraction pictures used in determining 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.

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— 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 phosphorus.

— Demonstrated that heat-killed material from bacteria could genetically transform live bacteria.

*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?

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

*21.DNA molecules of different sizes are often separated with the use of a technique called electrophoresis (see Chapter 14). 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?

*22. 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). Data from the DNA of several organisms analyzed by Chargaff are shown here.

23. Boris Magasanik collected data on the amounts of the bases of RNA isolated from a number of sources (shown in the next column), 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).

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

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

26. Heinz Shuster collected the following data on the base composition of the 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?

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*27.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 five-year-old daughter Sarah was able to draw a polynucleotide strand, but she made a few mistakes. Sarah’s diagram below contains at least 10 mistakes.

28.28.One nucleotide strand of a 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.

*29.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?

30.Which of the processes of information transfer illustrated in Figure 8.14 are required for the T2 phage reproduction illustrated in Figure 8.4?

*31.Compare and contrast prokaryotic and eukaryotic chromosomes. How are they alike and how do they differ?

*32.A diploid human cell contains approximately 6.4 billion base pairs of DNA.