Given below is the sequence of the coding strand of $DNA$ in a transcription unit: $5' - AATGCAGCTATTAGG - 3'$. Write the sequence of $(a)$ its complementary strand and $(b)$ the $mRNA$.

(N/A) The coding strand is $5' - AATGCAGCTATTAGG - 3'$. The complementary strand (template strand) runs in the $3' - 5'$ direction and is antiparallel to the coding strand. Therefore,the complementary strand sequence is $3' - TTACGTCGATAATCC - 5'$ or $5' - CCTAATAGCTGCATT - 3'$.
$(b)$ The $mRNA$ sequence is identical to the coding strand of $DNA$,except that $Thymine$ $(T)$ is replaced by $Uracil$ $(U)$. Thus,the $mRNA$ sequence is $5' - AAUGCAGCUAUUAGG - 3'$.