The essential building block of DNA is the nucleotide. Each nucleotide consists of three components: a phosphate group, a sugar molecule (deoxyribose), and a nitrogenous base. There are four types of nitrogenous bases in DNA: adenine, thymine, cytosine, and guanine, which pair specifically (adenine with thymine and cytosine with guanine) to form the double helix structure. The sequence of these nucleotides encodes genetic information, guiding the synthesis of proteins and influencing biological traits, making them fundamental to heredity and cellular function.