*33.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 properties of the genetic material on this planet?

34.How might ³²P and ³⁵S be used to demonstrate that the transforming principle is DNA? Briefly outline an experiment that would show that DNA, rather than protein, is the transforming principle.

35.Researchers have proposed that early life on Earth used RNA as its source of genetic information and that DNA eventually replaced RNA as the source of genetic information. What aspects of DNA structure might make it better suited than RNA to be the genetic material?

*36.Imagine that you are a student in Alfred Hershey and Martha Chase’s laboratory in the late 1940s. You are given five test tubes containing E. coli bacteria infected with T2 bacteriophages that have been labeled with either ³²P or ³⁵S. Unfortunately, you forget to indicate which tubes are 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 phage protein coats. You then centrifuge the contents to separate the protein coats and the cells, check for the presence of radioactivity, and obtain the results shown here. Which tubes contained E. coli infected with ³²P-labeled phage? Explain your answer.