Question

What did Meselson and Stahl observe when
They cultured E. coli in a medium containing `""^15Nh_4CL` for a few generations and centrifuged the content?
they transferred one such bacterium to the normal medium of `NH_4Cl` and cultured for 2 genretion ?
What did Meselson and Stahl conclude from this experiment? Explain With the help of diagram
Which is the first geretic material? Give reasons in support of your answer.

Answer 1

Meselson and Stahl obsered that in the E. coli bacterium the DNA becomes completely labelled with `N^15` medium by centrifugation for few genretion
·After two genretion density changed and showed equal amount of light DNA(`N^14`) and dark hybrid DNA `(N^14-N^15)`.
They concluded that DNA replicates semi-conservately. [For Figure See Q. 30. Set-I. Outside Delhi, 2008].
.RNA is the first genetic material.
RNA is highly reactive, and acts as a catalyst as well as genetic material.
Essential life processes such as metabolism, translation and splicing evolved around RNA.