Well if we talk about Nucleotides then it's RNA & DNA which are made up of Organic molecules. And when these molecules combines as a whole then it's called as Polynucleotide chain.

=> Or in simple words then Polynucleotide chain is the Chain of nucleotide.

=> A nucleotide has three components - N-base , Pentose sugar and Phosphate.

=> In N-base there are mainly 2 parts found - Purines and Pyramidines.

And Purines must bind with Purines so as to maintain the DNA helical structure.

=> These nitrogenous bases are linked to each other with H-bonding also the nitrogen base is linked to the pentose sugar with N-glycosidic bond.

=> When a phosphate group is linked to 5'-OH of a nucleotide via phosphodiester linkage , a corresponding nucleotide is formed.

=> More and more nucleotide can be joined in order to form a polynucleotide chain.A polymer thus formed has at one end a free phosphate moiety at 5'-end of the ribose sugar.

=> Similarly at the other end of the polymer the ribose has free 3'-OH Group which is refrerred as 3'-end of the polynucleotide chain.