Question

Which of the following mediums were used to culture bacteria by Meselson and Stahl in their experiments?

• A. ${}^{14}N{H}_{4}Cl$ and ${}^{15}N{H}_{4}Cl$
• B. CsCl
• C. Medium containing radioactive sulphur
• D. Medium containing radioactive phosphorus

Answer 1

The correct option is A ${}^{14}N{H}_{4}Cl$ and ${}^{15}N{H}_{4}Cl$

Meselson and Stahl utilised the technique of density gradient centrifugation in their experiments. They grew E.coli in a medium containing ${}^{15}N{H}_{4}Cl$. Consequently, all the DNA molecules got ${}^{15}N$ incorporated into them. After that, the cells were transferred into a medium containing normal $N{H}_{4}Cl$. The cells were isolated at different time intervals, their double stranded DNA was extracted and separated in CsCl density gradient.