LABORATORY REVIEW
MOLECULAR BIOLOGY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Only 14N DNA
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Only 15N DNA
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All DNA half 14N and half 15N
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Half the DNA with only 14N and half with only 15N
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Detailed explanation-1: -Meselson & Stahl reasoned that these experiments showed that DNA replication was semi-conservative: the DNA strands separate and each makes a copy of itself, so that each daughter molecule comprises one “old” and one “new” strand.
Detailed explanation-2: -Conclusion. The experiment done by Meselson and Stahl demonstrated that DNA replicated semi-conservatively, meaning that each strand in a DNA molecule serves as a template for synthesis of a new, complementary strand.
Detailed explanation-3: -Before beginning their analysis of DNA replication, Meselson and Stahl first showed that DNA made with regular 14N could be separated from DNA containing heavy 15N. They accomplished this by growing two separate batches of Escherichia coli bacteria, feeding each batch a different nitrogen isotope.
Detailed explanation-4: -They used heavy (N15) and light (N14) nitrogen, which is found in the nucleotides that make up the DNA. They aimed to differentiate between DNA samples depending on the weight or the position on a density gradient. Density-gradient centrifuge was a technique developed by Meselson himself.