What component is a nucleic acid determines the $5\text{'}$ free end?

The objective is to identify what component in the nucleic acid in$5\text{'}$free end

Nucleic acids are organic macromolecules that are present all over the cell. They were first discovered in the nuclei of cells. Nucleic acids, such as DNA and RNA, are found in all known forms of life.

One of the components of nucleotide structure is nitrogen bases. Purines and pyrimidines are nitrogen bases that form various nucleotide structures.

The backbone structure of nucleic acid is made up of phosphate and sugar. Both DNA and RNA have a sugar-phosphate backbone that serves as a structural foundation. The $5\text{'}$ free end of a nucleic acid is determined by the free phosphate group on the $5\text{'}$ carbon of the sugar unit (ribose or deoxyribose).