# The structure of nucleic acids. Type of connection between mononucleotides??

The other connection is a phospho-ester bond from the 5$hydroxy group on the ribose sugar to a phosphate group. These connections make up the monomers of nucleotides. All nucleotide monomers have 2 important reactive ends. The 5$Phosphate and the 3$Hydroxyl group on the ribose sugar. When 2 monomers for a dimer (dinucleotide), the 5$Phosphate of one monomer forms a phosphoester bond with the 3$hydroxyl group of the other monomer. The phosphate group that is linking them contains 2 ester bonds - one to each monomer. The linkage between the monomers in a dinucleotide is called a phospho-diester bond. Now your dinucleotide still has a free 3$ hydroxyl group, so the next monomer can add onto this site and you'll get a trimer...and on and on...to an oligonucleotide...polynucleotide, etc.