The primary constituents of a DNA molecule are nucleotides, which consist of a phosphate group, a sugar molecule, and a nitrogenous base. There are four types of nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The sequence of these bases encodes genetic information essential for cellular function and heredity. DNA’s double-helix structure, formed by complementary base pairing (A with T, and C with G), allows for accurate replication and transmission of genetic material across generations, critical for life processes.