If you were to repeat the Meselson Stahl experiments, but rather than use N15 and N14, you use P32 and P31, how would the result
ing DNA bands present in the CsCl gradient change? Remember the initial culturing of bacteria is in the heavy (H) isotope then moved to lighter (L) isotope.
(A) Only newly synthesized 'daughter strands would contain heavy P32
(B) No strands of DNA would incorporate light P31 as P is not used in the synthesis of nucleic acids.
(C) The banding pattern would not change and the results would be similar as if you had used N14 and N15
(D) You can't tell since Nitrogen and Phosphorus have different atomic masses, therefore, the relative positions of the resulting (HH, H:L and L:L) DNA bands would differ from what was observed in the Meselson Stahl experiment using heavy and light N.
(E) A and C are correct.
The CsCl gradient centrifugation in Meselson Stahl experiments is done to separate the bands of the DNA containing isotopes on the basis of difference in the density.
In the experiment, bacterial cultures were grown in the medium of 15N and 14N but if we repeat the experiment with P32 and P31 instead of 15N and 14N and centrifugation is performed then the banding pattern will be the same as of the previous experiment as the method of the replication is same that is semi-conservative.
