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  • "Use of heavy isotype of nitrogen by Meselson and Stahl demonstrated semi-conservative mode of replication of DNA molecule." Explain how did they arrive at this conclusion.    

"Use of heavy isotype of nitrogen by Meselson and Stahl demonstrated semi-conservative mode of replication of DNA molecule." Explain how did they arrive at this conclusion.

 

 

 

 
 
 
 
 

Answers (1)

Mathew Mesolon and Franklin Sthal performed the following experiment to show that DNA is semi-conservative -

  • They grow E.coli in a ^{15}NH_{4}Cl containing medium for many generations and the result was that ^{15}N was incorporated into newly synthesized DNA. This heavy DNA molecule could be distinguished from the normal DNA by centrifugation in CsCl density gradient.
  • They then transfused the cells into the medium with normal ^{15}NH_{4}Cl and took a sample at various definite time intervals as the cells multiplied and extracted the DNA that remained double-stranded helix. Various samples were separated independently on CsCl gradients to measure the density of DNA.
  • Thus the DNA that was extracted from the culture one generated after the transfer from ^{15}N to ^{14}N to medium (20 minutes) had a hybrid or intermediate density. DNA extracted from the culture after another generation (after 40 minutes, II generation) was composed of equal amounts of this hybrid DNA and of light DNA.
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Priyanka Kumari

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