In what direction does DNA polymerase add nucleotides to the new DNA strand?

DNA polymerase is an enzyme that plays a critical role in DNA replication by synthesizing new DNA strands. It adds nucleotides to the growing strand during the synthesis process. The important aspect of its activity is that it can only add nucleotides to the 3' end of a growing DNA strand, which means the synthesis always occurs in the 5' to 3' direction.

This specificity is due to the chemical nature of nucleotides, which consist of a phosphate group, a sugar, and a nitrogenous base. The 5' carbon of the sugar of one nucleotide attaches to the 3' hydroxyl (OH) group of the sugar of the previously added nucleotide, thus extending the chain. As a result, when a new nucleotide is added, it is added to the 3' end of the strand, pushing the overall direction of synthesis from the 5' end toward the 3' end. This is a fundamental principle of molecular biology that applies to DNA replication and is crucial for the proper copying and transmission of genetic information.