Nucleic acids are organic polymeric macromolecules composed of nucleotide monomers building blocks. A nucleotide is made of nucleobase, a five-carbon sugar and 1-3 phosphate groups. Though the nucleotide normally refers nucleoside monophosphate, now nucleoside diphosphate or nucleoside triphosphate are also belongs to nucleotides. The base in nucleotides can be either purine or pyrimidine. When the sugars are riboses, the nucleotides are ribonucleotides. While the sugars are deoxyriboses, the nucleotides are deoxyribonucleotides.