Question

DNA replication is always 5' to 3'. Explain what 5' to 3' means with respect to nucleotide subunits. Explain what activity of DNA polymerase necessitates that replication be 5' to 3' rather than 3' to 5'? What problems do you envision with 3’ to 5’ direction of DNA chain growth?

Answer 1

During the DNA replication, the DNA polymerase moves in 3’ to 5’ direction and adds nucleotides to the 3’ end of the newly synthesizing strand. Thus, the new strand elongates in 5’ to 3’ direction. The DNA polymerase can add thee nucleotides only to the 3’-OH group, which needs the primer activity. DNA polymerase runs only in 3’ to 5’ direction as it require the free hydroxyl group, which performs a nucleophilic attack (activated triphosphate group on the 5^th carbon), and the reaction proceeds exergonically. For the replication to occur in the direction of 3’ to 5’, a different enzyme is needed.