Nucleotides are held together by phosphodiester bonds. These bonds form between the phosphate group of one nucleotide and the hydroxyl group on the sugar (deoxyribose in DNA or ribose in RNA) of another nucleotide. This linkage creates the sugar-phosphate backbone of the DNA or RNA strand.
The phosphodiester bond is a type of covalent bond, which means it involves the sharing of electrons between atoms. This bond is strong and stable, which is essential for maintaining the integrity of the genetic information stored in DNA and RNA.
In summary, the phosphodiester bond is the key chemical bond that connects nucleotides in a DNA or RNA strand, forming the backbone of these crucial molecules.