Which one of the following bonds links two nucleotides in a nucleic acid?
Nucleic acids are directional molecules: 5' end is the end with free (unesterified) phosphate group. 3' end is the end with free OH group. Nucleic acid sequences are written in 5'-3' direction. During the synthesis of nucleic acids, 3' OH group of existing nucleotide is esterified to the 5' phosphoryl group of the incoming nucleotide 3'-5' phosphodiester bond.
3'-3' phosphodiester bond
3'-5' phosphodiester bond
5'-5' phosphodiester bond
5'-5' phosphotriester bond
Basics of DNA