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The Meselson And Stahl Experiment on DNA Replication MCQ - Practice Questions with Answers
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #NEET
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Messelson and Stahl Experiment is considered one the most difficult concept.
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Taylor conducted the experiments to prove semiconservative mode of chromosome replication on
Concepts Covered - 1
Messelson and Stahl Experiment
- It is now proved that DNA replicates semi conservatively. It was shown first in Escherichia coli and subsequently in higher organisms, such as plants and human cells.
- Mathew Meselson and Franklin Stahl proved experimentally that parental strands of a helix are distributed equally between the two daughter molecules.
- They grew E. coli in a medium containing 15NH4Cl (15N is the heavy isotope of nitrogen) as the only nitrogen source for many generations.
- The result was that 15N was incorporated into newly synthesized 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.
- The various samples were separated independently on CsCl gradients to measure the densities of DNA.
- Thus, the DNA that was extracted from the culture one generation after the transfer from 15N to 14N medium [that is after 20 minutes; E. coli divides in 20 minutes] had a hybrid or intermediate density.
- DNA extracted from the culture after another generation [that is after 40 minutes, II generation] was composed of equal amounts of this hybrid DNA and of ‘light’ DNA.
- Very similar experiments involving the use of radioactive thymidine to detect the distribution of newly synthesized DNA in the chromosomes were performed on Vicia faba (faba beans) by Taylor and colleagues in 1958.
- The experiments proved that the DNA in chromosomes also replicate semi conservatively.
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