PRIMARY STRUCTURE OF DNA

Chromosomal DNA is made up of long DNA molecules with the size MW 1.6 × 10⁶ to 2 × 10⁹.
A DNA polymer generally contains 10¹⁰ deoxynucleotides.
The four different types of bases that are present in the DNA molecules are adenine deoxynucleotides (dA), thymine deoxynucleotides (dT), guanine deoxynucleotides (dG), and cytosine deoxynucleotides (dC).
Nucleotides are connected to one another by covalent 3′-5′-phosphodiester linkage. The ester linkage of a single phosphate residue is with the 3′—OH of one nucleotide with 5′—OH group of ribose of the next molecule.
Phosphodiester linkage gives rise to a linear polydeoxynucleotide strand with two free ends on both sides.
Each strand has one free 5′phosphate group without phosphodiester linkage at one end, which is called the 5′ end. The opposite group is called the 3′ end.
The primary structure mainly consists of different deoxynucleotides in one strand joined together by phosphodiester linkages.
The backbone of the primary structure is sugar phosphate residues, while the purine and pyrimidine bases connected with the sugar residue project laterally from the backbone.

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