Deoxyribonucleic acid, also known as DNA, was discovered in 1953. It is the main carrier of all genetic information. It is made up of nucleotides, which serve as the basic building blocks. Each nucleotide is made up of a five carbon pentose sugar, a phosphate and one of the four existing nitrogenous bases. There are two categories of the nitrogenous bases; purines such as Adenine and Guanine, and pyrimidines, Thymine and Cytosine. The nucleotides pair up in the following manner; adenine with thymine and guanine with cytosine. The nucleotides are held by covalent bonds forming a basis which is referred to as a sugar-phosphate backbone. They are linked in a phosphodiester linkage, which means that 3’ carbon of one sugar is matched with 5’ carbon of another sugar.


DNA has two strands made up of the sugar-phosphate backbone. The two strands run antiparallel to each other meaning they run in opposite directions. They are also complementary to each other, which means sequence of nucleotides of one stand is matched up perfectly with the sequence of another. The two stands tie together into a double helix structure. There is hydrogen bonding between each nucleotide.
DNA pairing