High Quality Content by WIKIPEDIA articles! A phosphodiester bond is a group of strong covalent bonds between a phosphate group and two 5-carbon ring carbohydrates (pentoses) over two ester bonds. Phosphodiester bonds are central to all known life, as they make up the backbone of each helical strand of DNA. In DNA and RNA, the phosphodiester bond is the linkage between the 3` carbon atom of one sugar molecule and the 5` carbon atom of another; the sugar molecules being deoxyribose in DNA and ribose in RNA. Phosphodiester bonds are also found in O-phosphonolipids (phospholipids) .