Problem 17: A gene is made of DNA.

Experiment with rough and smooth Pneumococcus DNA.

HI! Avery and his group used S-strain DNA to transform rough-coat (R) strain to the smooth-coat (S) strain. You do a similar experiment except you use R DNA instead of S DNA. What happens? Would the R strain be transformed to the S strain? DNA is DNA, transformation will take place. (No, R to S transformation requires a special donor DNA.) R strain DNA will transform R to S, but at a much lower frequency. (No, R strain DNA cannot transform R to S.) R strain DNA can’t transform R to S. (That is correct) R strain DNA will transform R to S, but the new S will not be infectious. (No, there is no "new" S in this case.) The R strain is missing the gene that makes the sugar coat needed for virulence. So adding DNA from the R strain will not transform R to S. When Avery and his group isolated DNA, they noticed that the DNA solution was very viscous, thick, and stringy. When they incubated the DNA solution with DNase, the viscosity disappeared. The same result occurs if the DNA sample is vortexed. If you do an Avery transformation experiment using S-strain DNA that has been vortexed for a long time, it loses its transformation ability. Why? Vortexing breaks the DNA into small pieces. The genes are no longer intact. (That is correct) Vortexing mixes the DNA, and makes new DNA that doesn’t have the transforming ability. (No, vortexing merley breaks up the DNA, it does not make new DNA.) It’s not DNA after all that causes transformation. (No, DNA is the transforming principle.) Vortexing breaks the DNA backbone. As a result, large DNA molecules are broken into short pieces. It is unlikely that any of these short DNA pieces are long enough to contain an entire gene. You figure out a way to break the S strain's DNA molecule exactly in half, then separate the two halves. You then use each half in a transformation experiment. Half#2 doesn’t have the gene that transforms R to S. (That is correct.) Half#1 has all the genes, Half#2 is junk DNA. (No, you don’t know that Half#2 is junk DNA. You only know that it doesn’t have the transforming ability.) Half#1 worked this time, in another experiment Half#2 will work. (No, if Half#2 can’t transform, it doesn’t matter how many times you try.) Half#1 transforms the R strain to S. This means that the gene for transformation is somewhere on that piece of DNA. Half#2 can’t transform because it doesn’t have the gene. CONGRATULATIONS!!! YOU'RE SO SMART!

dna transformation, dna molecules, rough coat, smooth coat, pneumococcus, sugar coat, transforming principle, virulence, avery

  • ID: 16393
  • Source: DNALC.DNAFTB

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