Question

Why DNA replication occur from 5' to 3' end?

Answer 1

~cos of nature of DNA polymerase. It recognizes n catalyze nucleophilic attack of 3' hydroxyl on nucleotide triphosphate (specifically on the deoxyribose sugar). Thats why 3' hydroxyl group must be available to act as a "starting block" for DNA synthesis.
~Because a 3' hydroxyl, new nucleotides only be added in the 3' direction. (extending sequence from 5' to 3').
~free hydroxyl is lost when new nucleotide added (ester bond forms between attached nucleotides), and new nucleotide has the free hydroxyl.
~new nucleotide then add onto the 3' end of the growing strand in the same way, such that you see it grows "toward" the 3' ... or rather 5' to 3'