DNA is a double-stranded molecule but only one strand act as the template for RNA polymerase to synthesize mRNA. The template strand is also called non-coding strand and another strand is called the coding strand.
The coding strands are in 5'to 3' direction and the non-coding strand is in 3' to 5' direction. So the template strand is read in 3' to 5' direction by RNA polymerase and mRNA is formed in 5' to 3' direction.
The sequence of nucleotide on mRNA are called codons and three codon are responsible for coding one amino acid.
