During DNA replication, in which direction is the new strand synthesized?

During DNA replication, new strands of DNA are synthesized in the 5' to 3' direction. This is intrinsic to the mechanism of DNA polymerases, the enzymes responsible for adding nucleotides to the growing strand. DNA strands have a polarity that is determined by the orientation of their sugar molecules. The 5' end has a phosphate group, while the 3' end has a hydroxyl group.

During replication, DNA polymerase can only add nucleotides to the 3' end of the growing strand. This means that as the enzyme traverses along the template strand in the 3' to 5' direction, it adds nucleotides to the 3' end of the newly synthesized strand, building it in a 5' to 3' direction.

This synthesis direction ensures that the new strand maintains the proper orientation for the hydrogen bonding between complementary bases and is crucial for the integrity and accuracy of DNA replication. Thus, the synthesis of the new DNA strand occurs only in the 5' to 3' direction.