Biol302 Quiz 9April 13th, 2011Name______

Question 1:(5pts)

Meselson and Stahl used N15 labeling to provide greater density to the DNA as compared to N14 (which normally occurs).

In nature, P31 is the normal atomic weight for phosphorous.

Theoretically speaking, could a scientist use P32 to increase the density of DNA?

Yes/No (Circle One)

If you answered Yes, then which phosphate residue of dATP, dTTP, dCTP or dGTP would need to be labeled with P32? The alpha, beta and/or gamma phosphate

Circle all phosphates that when labeled would get incorporated into replicating DNA.

If you answered No, then explain your answer.

Question 1a: (2 pts)

Excluding Nitrogen and Phosphorous, name another periodic element and its isotope that would increase the density of DNA when incorporated.

Question 2: (3pt).

Semi-conservative replication reveals that during mitosis of a cell, one template strand and one de novo synthesize strand are the foundations for each new cell created.

As predicted, Meselson and Stahl could see that there was DNA of intermediate density between the pure N14 and pure N15 after one cell division. This potential hybrid of N14 and N15 labeled DNA was actually shown to be a hybrid by what experiment? (Short answer)

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Question 3: (10 pts)

Meselson and Stahl obtained data in A to C.

If Meselson and Stahl had obtained results D and E

(Please assume that the individual bands in E are the same intensity as the band in D),

then please draw for me a plausible model* for how DNA replication after 1 cell division would give results shown in E.

Please show in your model (drawing) a step-by-step depiction for how this would actually happen in the cell. * I will accept several different plausible models as the correct answer.

In class question (extra credit)

Part 1: (3pts)

Why does one add EtBr to CsCl gradients for the isolation of plasmid DNA?

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Part 2: (4pts)

Given that the GC to AT ratios remain constant:

Is an 8kb supercoiled plasmid more dense than a 3kb supercoiled plasmid.

Yes/No (circle one)

Will an 8kb supercoiled plasmid have more EtBr bound to it than would a 3kb supercoiled plasmid? Yes/No (circle one)