Bauman Chapter 8 Answers to Critical Thinking Questions Chapter 8 p. 244 Even though some students correctly synthesize a fluorescent cDNA probe complementary to mRNA for a particular yeast protein, they find that the probe does not attach to any portion of the yeast’s genome. Explain why the students’ probe does not work. The cDNA probe sequence spans a splice junction in the mRNA, therefore there is no sequence in the genome that corresponds to the probe sequence. The short sequences in the genomic DNA flanking the splice junction are insufficient to form a stable duplex with the cDNA probe. p. 252 If the restriction enzymes HindIll and BamHl together produce restriction fragments 1.08 kbp and 1.32 kbp, then which of the three maps shown in Figure 8.10 is correct? The map on the left in Figure 8.10 is the correct map of the plasmid. The total plasmid length is 2.4 kbp. In the left hand map the distances between the HindIII and BamHI sites are 45% (1.08 kbp) and 55% (1.32 kbp) apart. p. 261 1. Examine the restriction sites listed in Table 8.1. Which restriction enzymes produce restriction fragments with sticky ends? Which produce fragments with blunt ends? Restriction enzymes BamHI, EcoRI, HindIII, and HinfI produce sticky ends. Restriction enzymes EcoRII, HindII, HpaI, MspI, and SmaI produce blunt ends. 2. A cancer-inducing virus, HTLV-1, inserts itself into a human chromosome, where it remains. How can a laboratory technician prove that a patient is infected with HTLV-1? The technician can design a DNA probe—a radioactive or fluorescent DNA strand that is complimentary to a specific sequence found in HTLV-1 but not in the human genome. Hybridization of the probe with DNA from a patient, as visualized by finding radioactivity or fluorescence in the hybrid DNA, demonstrates the presence of HTLV-1 DNA in the sample. 3. A thermocycler uses DNA polymerase from hyperthermophilic prokaryotes, but it cannot use DNA polymerase derived from Escherichia coli. Why not? The temperature used in a thermocycler for DNA amplification far exceeds the temperature maximum of mesophilic Escherichia coli, therefore DNA polymerase of E. coli would denature and lose function in a thermocycler.