Messelson and stahl experiment in point wise
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Messelson and Stahl conducted an experiment to prove that DNA replication is semi-conservative.
- They grow bacterium E. Coli in a medium containing nitrogen salts (15NH4Cl) labelled with radioactive 15N.
- 15N was incorporated into both the strands of DNA and such a DNA was heavier than the DNA obtained from E.Coli grown on a medium containing 14N.
- Then they transferred the E.Coli cells on to a medium containing 14N.
- After one generation, when one bacterial cell has multiplied into two, they isolated the DNA and evaluated its density.
- Its density was intermediate between that of the heavier 15N- DNA and lighter 14N-DNA.
- This is because during replication, new DNA molecule with one 15N old strand and complementary 14N new strand was formed( semi-conservative replication) and so its density is intermediate between the two.
- They grow bacterium E. Coli in a medium containing nitrogen salts (15NH4Cl) labelled with radioactive 15N.
- 15N was incorporated into both the strands of DNA and such a DNA was heavier than the DNA obtained from E.Coli grown on a medium containing 14N.
- Then they transferred the E.Coli cells on to a medium containing 14N.
- After one generation, when one bacterial cell has multiplied into two, they isolated the DNA and evaluated its density.
- Its density was intermediate between that of the heavier 15N- DNA and lighter 14N-DNA.
- This is because during replication, new DNA molecule with one 15N old strand and complementary 14N new strand was formed( semi-conservative replication) and so its density is intermediate between the two.
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