On which end are nucleotides added to a DNA molecule?

Nucleotides are added to the 3' end of a DNA molecule during DNA synthesis. This process occurs in the context of DNA replication and transcription, where DNA polymerase synthesizes a new strand by adding nucleotides to the growing strand. The enzyme can only attach a new nucleotide to the hydroxyl group present at the 3' carbon of the last nucleotide in the chain, which is why growth can only occur in the 5' to 3' direction. Thus, the new nucleotide’s phosphate group forms a bond with the 3' hydroxyl of the previous nucleotide, extending the strand. This unidirectional synthesis is essential for maintaining the integrity of the genetic information during cell division and the process of gene expression.