The 5' is upstream; the 3' is downstream. DNA and RNA are synthesized in the 5' to 3' direction In DNA Replication whenever synthesis occurs new nucleotide is added to 3' end In transcription, RNA is getting synthesized in 5' to 3' direction RNA editing It occurs in 3'-5' direction Post transcriptional modification in which differential RNA processing occurs. Also called chemical modification of RNA, in which mostly Cytosine gets conveed to Uracil. DNA Replication ,Proof reading DNA Repair 3'-5' exonuclease activity Mostly endonuclease activity, but sometimes it is 5'-3' exonuclease activity.