DNA is always synthesized in the 5'-to-3' direction, meaning that nucleotides are added only to the 3' end of the growing strand. As shown in Figure 2, the 5'-phosphate group of the new nucleotide ...

At this point, RNA polymerase begins moving down the DNA template strand in the 3' to 5' direction ... called a poly-A tail is added to the 3' end of the mRNA molecule (Figure 7).