Phosphate ester linkage is the covalent bond that will connect the sugar molecules with the backbone. This linkage occurs between 3’ carbon of one sugar to the 5’ carbon of the adjacent carbon. The phosphate will provide a negative charge and maintain the stability.
On the other hand, the heterocyclic base is attached to the Carbon-1’ of both DNA and RNA sugar molecules. The bases present in them are adenine, guanine, cytosine, uracil and thymine.