In Meselson and Stahl's experiment,what kind of DNA molecules would be found after four replication cycles? A)Only heavy DNA (¹⁵N-¹⁵N) B)Only intermediate DNA (¹⁵N-¹⁴N) C)Only light DNA (¹⁴N-¹⁴N) D)Both heavy (¹⁵N-¹⁵N)and light DNA (¹⁴N-¹⁴N) E)Both heavy (¹⁵N-¹⁵N)and intermediate DNA (¹⁵N-¹⁴N)

Question

Quizplus · Accepted Answer

Meselson and Stahl's experiment involved the use of heavy nitrogen (15N) to label DNA in E. coli, which was then allowed to replicate in a medium containing only light nitrogen (14N). The heavy nitrogen and light nitrogen can be distinguished based on their different densities in a cesium chloride (CsCl) gradient. After one replication cycle, the DNA would be either composed of one heavy and one light strand (intermediate) or two heavy strands (heavy), depending on the mode of replication (conservative or semi-conservative). After two replication cycles, both intermediate (one heavy and one light strand) and light (two light strands) DNA would be present. After four replication cycles, only light (two light strands) or a mixture of light (two light strands) and heavy (two heavy strands) DNA would be present. As the experiment was only conducted for two replication cycles, choice D is the best option as it includes both heavy (¹⁵N-¹⁵N) and light (¹⁴N-¹⁴N) DNA.

In Meselson and Stahl's Experiment,what Kind of DNA Molecules Would