The deoxyribonucleic acid (DNA) molecule consists of two single-strands, which are composed of four different types of nucleotide bases: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C). These two DNA strands run in an anti-parallel direction to each other. According to the base-pairing rules, Adenine always pairs with Thymine, while Guanine always pairs with Cytosine. In DNA, Thymine and Adenine form two hydrogen bonds between them, while Guanine and Cytosine form three hydrogen bonds between them.
