DNA is a double-stranded nucleic acid that contains the genetic information for cell growth, division, and function. It is composed of nucleotides, which are the building blocks and contain a sugar, phosphate, and one of four nitrogenous bases. The bases on one strand form hydrogen bonds with complementary bases on the other strand in specific base pairing - adenine bonds with thymine and cytosine bonds with guanine - which allows the two strands to bond together in the DNA double helix structure. DNA is further packaged in the cell by winding around histone proteins to form nucleosomes.