DNA is composed of phosphate, a sugar and 4 nitrogenous bases. These bases are Adenine, Thymine, Cytosine and Guanine. They are organic molecules that have a large amount of nitrogen contained within them that is relative to their overall mass and are proton acceptors that tend to carry a net positive charge. Adenine and Guanine are classified as purines while Thymine and Guanine are pyrimidines which are all non-polar and planar molecules. Purines are six membered rings fused to a five-member ring and between them, the rings include 4 nitrogen atoms and five carbon atoms. On the other hand, pyrimidines have only a six-membered ring which has two nitrogen atoms and four carbon atoms. Each base also has other constituents projecting from the ring. These bases are bonded together in pairs and due to the large structure of purines and the small structure pyrimidines, they are bonded opposite to each other and therefore Adenine is bonded to Thymine and Cytosine is bonded to Guanine. They are bonded together with hydrogen bonds: Adenine and Thymine having one H-N and one H-O bond while Cytosine and Guanine have two H-N and one H-O bond. Adenine Represented by the letter A, its chemical formula is C5H5N5. Guanine Represented by the letter G, its chemical formula is C5H5N5O. Thymine Represented by the letter T, its chemical formula is C5H6N2O2. Cytosine Represented by the letter C, its chemical formula is C4H4N2O2. Nucleotides vs Nucleosides Nucleotides and nucleosides are structurally similar molecules, only having one small difference. Although the difference is small, it causes a difference in their functions. Nucleotides are molecules made up of a sugar, nitrogenous base and phosphate while nucleosides are made up of just a sugar and nitrogenous base. Nucleotides polymerize and form nucleic acids as well as act like energy storing molecules while nucleosides are anticancer compounds that have antiviral properties. References: https://www.differencebetween.com/difference-between-nucleotide-and-vs-nucleoside https://www.diffen.com/difference/Nucleoside_vs_Nucleotide https://www.thoughtco.com/nitrogenous-bases-definition-and-structures-4121327 https://sciencing.com/what-four-nitrogenous-bases-dna-4596107.html http://www.phschool.com/science/biology_place/biocoach/bioprop/dnabase.html
