Challenge Questions

30. Suppose that an automated, unmanned probe is sent into deep space to search for extraterrestrial life. After wandering for many light-years among the far reaches of the universe, this probe arrives on a distant planet and detects life. The chemical composition of life on this planet is completely different from that of life on Earth, and its genetic material is not composed of nucleic acids. What predictions can you make about the chemical properties of the genetic material on this planet?

31. How might 32P and 35S be used to demonstrate that the transforming principle is DNA? Briefly outline an experiment that would show that DNA and not protein is the transforming principle.

32. Scientists have reportedly isolated short fragments of DNA from fossilized dinosaur bones hundreds of millions of years old. The technique used to isolate this DNA is the polymerase chain reaction (PCR), which is capable of amplifying very small amounts of DNA a millionfold (see Chapter 16). Critics have claimed that the DNA isolated from dinosaur bones is not of ancient origin but instead represents contamination of the samples with DNA from present-day organisms such as bacteria, mold, or humans. What precautions, analyses, and control experiments could be carried out to ensure that DNA recovered from fossils is truly of ancient origin?

SUGGESTED READINGS]_

Avery, O. T., C. M. MacLeod, and M. McCarty. 1944. Studies on the chemical nature of the substance inducing transformation of pneumococcal types. Journal of Experimental Medicine 79:137 -158.

Avery, MacLeod, and McCarty's paper describing their demonstration that the transforming principle is DNA.

Crick, F. 1988. What Mad Pursuit: A Personal View of Scientific Discovery. New York: Basic Books.

Francis Crick's personal account of the discovery of the structure of DNA. Dickerson, R. E., H. R. Drew, B. N. Conner, R. M Wing, A. V. Fratini, and M. L. Kopka. 1982. The anatomy of A-, B-, and Z-DNA. Science 216:475 -485.

A review of differences in secondary structures of DNA. Fraenkal-Conrat, H., and B. Singer. 1957. Virus reconstitution II: combination of protein and nucleic acid from different strains. Biochimica et Biophysica Acta 24:540 - 548.

Report of Fraenkal-Conrat and Singer's well-known experiment showing that RNA is the genetic material in tobacco mosaic virus. Griffith, F. 1928. The significance of pneumoncoccal types. Journal of Hygiene 27:113 - 159.

Griffith's original report of the transforming principle.

Handt, O., M. Richards, M. Trommsdorff, et al. 1994. Molecular genetic analysis of the Tyrolean Ice Man. Science 264:1775 -1778.

Describes the isolation and analysis of DNA from a 5000-year-old frozen man found on a glacier in the Alps.

Hershey, A. D., and M. Chase. 1952. Independent functions of viral protein and nucleic acid in growth of bacteriophage. Journal of General Physiology 36:39 - 56. Original report of Hershey and Chase's well-known experiment with T2 bacteriophage. Judson, H. F. 1996. The Eighth Day of Creation: Makers of the Revolution in Biology, expanded edition. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press. A comprehensive account of the early years of molecular genetics.

Miescher, F. 1871. On the chemical composition of pus cells. Hoppe-Seyler's Med.-Chem. Untersuch. 4:441 - 460. Abridged and translated in Great Experiments in Biology, M. L. Gabriel, and S. Fogel (Eds.). Englewood Cliffs, NJ: Prentice-Hall, 1955. An abridged and translated version of Miescher's original paper chemically characterizing DNA. Mirsky, A. E. 1968 The discovery of DNA. Scientific American 2 (6):78 - 88.

A good account of the discovery of DNA structure.

Rich, A., A. Nordheim, and A. H.-J. Wang. 1984. The chemistry and biology of left-handed Z-DNA. Annual Review of Biochemistry 53:791 - 846.

Good review article on the structure and possible function of Z-DNA.

Watson, J. D. 1968. The Double Helix. New York: Atheneum.

An excellent account of Watson and Crick's discovery of DNA. Watson, J. D., and F. C. Crick. 1953. Molecular structure of nucleic acids: a structure for deoxyribose nucleic acids. Nature 171:737 - 738.

Original paper in which Watson and Crick first presented their new structure for DNA.

Zimmerman, S. B. 1982. The three-dimensional structure of DNA. Annual Review of Biochemistry 51:395 - 427. Review of the different secondary structures that DNA can assume.

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