The product and density of DNA after one and two rounds of replication if Meselson and Stahl had started their experiment with 14 N light DNA and then transferred them into 15 N heavy DNA medium. Concept introduction: Meselson and Stahl performed an experiment to prove that DNA (deoxyribonucleic acid) replicates in a semi-conservative manner. They first grew bacterial cells in 15 N medium, so that the DNA of the bacterial cells would only contain pure 15 N DNA. Afterwards, these cells were transferred into 14 N medium. After one round of replication, DNA was centrifuged to observe their density in a solution containing cesium chloride. The density of parental DNA ( 15 N/ 15 N) was found to be 1.722 g/cm 3 and a single band was formed. The density of the DNA after replication was found to be 1.715 g/cm 3 , which is the expected density of duplex containing one heavy and one light strand. Thus, they proved that DNA replicates in a semi-conservative manner.

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Chapter 12.1, Problem 1SAQ

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To determine:

The product and density of DNA after one and two rounds of replication if Meselson and Stahl had started their experiment with ¹⁴N light DNA and then transferred them into ¹⁵N heavy DNA medium.

Concept introduction:

Meselson and Stahl performed an experiment to prove that DNA (deoxyribonucleic acid) replicates in a semi-conservative manner. They first grew bacterial cells in ¹⁵N medium, so that the DNA of the bacterial cells would only contain pure ¹⁵N DNA. Afterwards, these cells were transferred into ¹⁴N medium.

After one round of replication, DNA was centrifuged to observe their density in a solution containing cesium chloride. The density of parental DNA (¹⁵N/¹⁵N) was found to be 1.722 g/cm³and a single band was formed. The density of the DNA after replication was found to be 1.715 g/cm³, which is the expected density of duplex containing one heavy and one light strand. Thus, they proved that DNA replicates in a semi-conservative manner.

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