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Question
A cell is grown in a solution containing radioactive nucleotides for one generation. It is removed from the radioactive solution and grown in a normal medium in the next generation. If a dotted line represents a radioactive DNA strand and a solid line represents a non-radioactive DNA strand, which of the following depicts the DNA of the four cells in the second generation?
(correct answer + 2, wrong answer - 0.50)
A cell is grown in a solution containing radioactive nucleotides for one generation. It is removed from the radioactive solution and grown in a normal medium in the next generation. If a dotted line represents a radioactive DNA strand and a solid line represents a non-radioactive DNA strand, which of the following depicts the DNA of the four cells in the second generation?
(correct answer + 2, wrong answer - 0.50)
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Solution
The correct option is D
Matthew Meselson and Franklin Stahl grew E. coli in a medium containing ammonium chloride with heavy isotope of nitrogen - 15Nas the only nitrogen source for many generations. The result was that 15N was incorporated into newly synthesised DNA (as well as other nitrogen containing compounds).
Then they transferred the cells into a medium with normal 14NH4Cl and took samples at various definite time intervals as the cells multiplied, and extracted the DNA that remained as double-stranded helices.
Messelson and Stahl’s Experiment
Matthew Meselson and Franklin Stahl grew E. coli in a medium containing ammonium chloride with heavy isotope of nitrogen - 15Nas the only nitrogen source for many generations. The result was that 15N was incorporated into newly synthesised DNA (as well as other nitrogen containing compounds).
Then they transferred the cells into a medium with normal 14NH4Cl and took samples at various definite time intervals as the cells multiplied, and extracted the DNA that remained as double-stranded helices.
Messelson and Stahl’s Experiment