And this is what we call the backbone of that sugar, of that nucleic acid. So the backbone of that nucleic acid consists of a chain of repeating sugar phosphate units as shown in the following diagram. And by the way, these are the bases, the third component of a nucleotide attached to this carbon number one of each one of these sugars. And we'll discuss what these nitrogenous bases are in just a moment. These bases are not part of that backbone of the nucleic acid because unlike these, the bases do actually change as we go from one nucleotide to another nucleotide. So the backbone that does not consist of these bases, but consists of these repeating units, does not change and remains constant throughout that entire nucleic acid.