The double-helical structure of $DNA$ is due to ....

What are the positions of $N$ atoms present in the purine ring of nucleic acids?

Given below are two statements:
Statement $I$: $A$ unit formed by the attachment of a base to $1'-$position of sugar is known as nucleoside.
Statement $II$: When nucleoside is linked to phosphorous acid at $5'-$position of sugar moiety,we get nucleotide.
In the light of the above statements,choose the correct answer from the options given below:

Codon is present in

Which base is present in $RNA$ but absent in $DNA$?

If one strand of a $DNA$ has the sequence $ATGCTTCA$,the sequence of the bases in the complementary strand is: