UPSC 2017 CDS I GK Paper

Polynucleotide chain of DNA contains a nitrogenous base, deoxyribose sugar and phosphate group. The nucleotide of DNA consists of a deoxyribose sugar molecule to which is attached a phosphate group and one of the four nitrogenous bases: two purines (adenine and guanine) and two pyrimidines (cytosine and thymine).