The nucleotides in a single polynucleotide chain are linked together by covalent phosphodiester bonds. These bonds form between the 5' phosphate group of one nucleotide and the 3' hydroxyl (-OH) group of the sugar (pentose) of the adjacent nucleotide. This linkage creates a sugar-phosphate backbone with alternating sugar and phosphate groups, while the nitrogenous bases extend from the sugar as side groups. The chain has directionality, with a free 5' phosphate group at one end and a free 3' hydroxyl group at the other, giving the strand a 5' to 3' polarity. The enzyme polymerase catalyzes the formation of these phosphodiester bonds during nucleotide polymerization.
In summary:
- Nucleotides are joined through phosphodiester bonds.
- The bond connects the phosphate on the 5' carbon of one sugar to the 3' carbon hydroxyl group of the next sugar.
- This linkage forms the sugar-phosphate backbone of the polynucleotide chain.
- The chain has distinct 5' and 3' ends, indicating chemical polarity.
- Nitrogenous bases are not bonded to each other but project from the sugar-phosphate backbone.
This linkage mechanism applies to both DNA and RNA polynucleotide chains.
