During DNA synthesis, where are the nucleotides added?

The process of DNA synthesis, also known as DNA replication, involves the addition of nucleotides to the growing DNA strand at its 3' end. This is a fundamental aspect of how DNA polymerases, the enzymes responsible for synthesizing new DNA strands, operate. Each nucleotide that is added has a phosphate group on its 5' carbon and an OH group on its 3' carbon. When a new nucleotide is incorporated, its 5' phosphate group forms a covalent bond with the OH group on the 3' carbon of the last nucleotide in the chain, effectively extending the strand.

This directionality is pivotal because it ensures that DNA replication can proceed accurately and efficiently, maintaining the integrity of the genetic information being copied. The specific addition of nucleotides in this manner is a characteristic feature of DNA synthesis, distinguishing it from other processes such as RNA synthesis, where a similar principle applies but may involve different specificities.