Fosfodiester

Fosfodiester, commonly referred to as the phosphodiester bond, is the covalent linkage that connects nucleotides within nucleic acids. In DNA and RNA, a phosphodiester bond forms between the 5' phosphate group of one nucleotide and the 3' hydroxyl group of the next, creating the sugar-phosphate backbone that runs in a 5' to 3' direction.

Chemically, a phosphodiester bond involves a phosphorus atom bound to two sugar-derived esters. The bond is formed by a condensation reaction during nucleotide polymerization, typically driven by enzymes such as DNA or RNA polymerases and, in cells, coupled to the hydrolysis of nucleoside triphosphates. The resulting backbone is highly negatively charged at physiological pH due to the phosphate groups.

Phosphodiester bonds are relatively stable under normal cellular conditions but can be hydrolyzed by nucleases, including DNases and RNases, or under acidic or basic conditions. Cleavage produces fragments with 5' phosphate and 3' hydroxyl ends, a property exploited in processes such as DNA sequencing and RNA processing.

The phosphodiester backbone imparts directionality to nucleic acids and is essential for the replication, transcription, and translation machinery of cells. In biotechnology, synthetic oligonucleotides are manufactured with phosphodiester linkages, though these can be chemically modified (for example, to phosphorothioate bonds) to improve stability for therapeutic or diagnostic applications.

See also: nucleic acids, nucleotides, phosphodiesterase.