Which one of the following is called polynucleotide joining enzyme
Polymerase $I$
Polymerase $II$
Ligase
Ribonuclease
For proving the semi conservative mode of replication of $DNA$ , $E-coli$, were first grown in the medium containing ?
Ten E.coli cells with ${ }^{15} N$ - dsDNA are incubated in medium containing ${ }^{14} N$ nucleotide. After 60 minutes, how many E.coli cells will have DNA totally free from $15\,N$ ?
Escherichia coli fully labelled with $15 \mathrm{~N}$ is allowed to grow in $14 \mathrm{~N}$ medium. The two strands of $DNA$ molecule of the first generation bacteria have
Discuss the significance of heavy isotope of nitrogen in the Meselson and Stahl’s experiment.
In Meselson and Stahl's experiments, heavy $DNA$ was distinguished from normal $DNA$ by centrifugation in