DNA is created by adding a nucleotide to the 3' end of an elongating 5'->3' strand. Of course, the template strand is "read" in the opposite direction: 3'->5'.
mRNA is translated by "reading" it in the 5'->3' direction. The protein residues are added by reading the frame from 5'->3'.
As there always both 3'-5' and 5'-3' strands during replication, it is of importance that you understand which strand is elongating and which strand is being "read". Note that DNA replication occurs in both directions from the Origin of Replication, but DNA polymerization will only add nucleotides to the 3' end of an elongating 5'->3' strand, which is why there's a confusion: There are TWO lagging strands, and TWO leading strands, one in each direction following one of two helicases unwinding outward from the replication bubble.
The Eukaryotic DNA Pol are alpha (short leading strand with RNA primase activity), epsilon (leading strand), delta (lagging strand), and gamma (mitochondrial), plus a few others that you don't need to know. They all have 3'->5' exonuclease activity for proofreading (which is backtracking on their primary 5'->3' polymerase activity). RNA priming is done by RNA Primase, also in the 5'->3' direction.
Transcription is done by RNA Pol II in Eukaryotes, "reading" the DNA from the 3'->5' and synthesizing new mRNA by adding nucleotides on at the 3' end on the elongating 5'->3' mRNA.
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If all else fails, remember that you add on nucleotides AND proteins at the 3' end.
