What does the 3' end of a DNA strand refer to?

The 3' end of a DNA strand is referred to as the end that has a hydroxyl group (-OH) attached to the 3rd carbon of the sugar in the nucleotide. In the structure of DNA, nucleotides are connected through phosphodiester bonds, which link the 5' phosphate group of one nucleotide to the 3' hydroxyl group of another. This orientation is crucial for understanding DNA replication and transcription, as nucleic acid synthesis occurs in a 5' to 3' direction, meaning new nucleotides are added to the hydroxyl group of the growing chain.

This structural feature is essential for maintaining the integrity of genetic information and allows the enzymes involved in DNA synthesis to recognize where to attach the new nucleotides, thus ensuring accurate copying of the DNA sequence during replication. The distinction between the 5' and 3' ends is vital in molecular biology for discussing DNA and RNA function and structure.