Nucleotide monomers are linked together into a single strand via condensation reactions (water produced as a by-product)

• The phosphate group of one nucleotide attaches to the sugar of another nucleotide (at the 3’–hydroxyl position)
  

• This results in a covalent phosphodiester bond forming between the two nucleotides
  

Successive condensation reactions result in the formation of long polynucleotide strands

• The sugar and the phosphate form a ‘backbone’, while the nitrogenous bases extend out from this strand
  

Sugar-Phosphate Backbone