Final answer:
In polynucleotides, the individual nucleotides are linked by phosphodiester bonds between the sugar of one nucleotide and the phosphate group of another. This linkage forms the backbone of the DNA or RNA molecule, with the nitrogenous bases extending outwards.
Step-by-step explanation:
In a polynucleotide, the individual nucleotides are linked by phosphodiester bonds between sugar and phosphate groups. Specifically, the phosphate group of one nucleotide is covalently bonded to the sugar molecule of the next nucleotide.
This bonding occurs between the hydroxyl group (OH) at the 3' carbon of one nucleotide's sugar and the phosphate attached to the 5' carbon of the adjacent nucleotide, creating a backbone that is consistent throughout the DNA or RNA molecule.
The alternating pattern of sugar and phosphate groups forms the backbone of the polynucleotide chain, with the nitrogenous bases protruding from this backbone.
Among these bases, there are four different types in DNA: adenine (A), guanine (G), cytosine (C), and thymine (T); in RNA, uracil (U) replaces thymine. These bases do not bond with the sugars and phosphates to form the backbone; rather, in the case of DNA, they pair with complementary bases on the opposite strand via hydrogen bonds to form the structure of the double helix.