The Mystery of the Saguaro Measles: Chapt 3

..... While the group was sitting in the Circus-Circus buffet watching the throngs of families passing by with full trays of food, they were also discussing their recent results and wondering what to do next. ..Mary Lou piped up: .."Since it seems to be heat that is killing the measles, maybe we could heat the RNA and see what happens - does it roast or not!" ..Jason went wide-eyed: "That's it! Let's get going." ..Mary Lou was very proud of herself, but, as we know, Jason had other ideas. ..He told Wilbie to see if he could procure some T4-DNA, some synthetic dsRNA, and some TMV-RNA. ..Meanwhile Cheryl suggested that she and Jim look around for a UV spectrophotometer at UNLV. ..Jason would look into getting use of a large water bath that could be heated to boiling. ..Mary Lou was assigned the most important task of scouting out the Hard Rock Café about a block off the UNLV campus. ..This they would make their meeting base while an extended experiment went on.

..... Wilbie could find only T4-DNA and TMV-RNA, while the others got together all the equipment they needed. ..Mary Lou found the pastries excellent, and didn't return for a long time. ..The group took samples of each type of nucleic acid (including the saguaro virus RNA, and the RNase-treated material that Cheryl and Jim had made the previous day) and put them in tubes that were immersed in the waterbath filled with cool water. ..The bath was turned to high, and as the temperature rose, the optical densities at 260 nm of each tube were periodically noted. ..Once the bath came to a boil, they cleaned up and met at the Hard Rock to discuss their results of this hyperchromic effect experiment.

Your answer should respond to at least these questions:

• What is the molecular reason that the OD of the DNA rises sigmoidally sharply for three of the four samples? ..(I.e.: what is the molecular basis for the hyperchromic effect?) ..(Hint: ..addition of glycerol raises the inflection temperature, which is called the T_m)
• How is that the RNase-treated saguaro virus RNA shows a higher hyperchromic effect than does the untreated virus RNA, even though it has a lower T_m?
• Draw a picture of the saguaro virus genome, showing what is sensitive to the RNase.
• What might the steepnesses of the various inflections mean?
• What might be the reason for some inflections being at lower temperatures? ..Here it is shown that T4-DNA inflects at about 83°, while saguaro virus RNA is about 78°.