Structure of Polynucleotide Chain:  A nucleotide has three components – a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and a phosphate group. There are two types of nitrogenous bases – Purines (Adenine and Guanine), and Pyrimidines (Cytosine, Uracil and Thymine). Cytosine is common for both DNA and RNA and Thymine is present in DNA. Uracil is present in RNA at the place of Thymine.

Formation of Polynucleotide Chain

• The nitrogenous bases can be grouped as either purines or pyrimidines. The purines include adenine and guanine. The pyrimidines include cytosine, thymine and uracil.
• The first carbon of the pentose sugar is attached to the nitrogenous base with the help of an N-glycosidic linkage.
• The third carbon atom of the pentose sugar combines with the phosphate group by a covalent bond. This linkage is the phosphodiester bond.
• The sugar and phosphate form a solid backbone to the polynucleotide chain.
• This polynucleotide monomer (sugar, phosphate and nitrogenous base) combines to form a polynucleotide chain.

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By Team Learning Mantras