DNA is known for its familiar twisted shape. This shape is often described as a spiral staircase or twisted ladder. DNA is a nucleic acid with three main components: nitrogenous bases, deoxyribose sugars, and phosphate molecules. Interactions between water and the molecules that compose DNA cause this nucleic acid to take on a twisted shape. This shape aids in the packing of DNA into chromatin fibers, which condense to form chromosomes. The helical shape of DNA also makes DNA replication and protein synthesis possible. When necessary, the double helix unwinds and opens to allow DNA to be copied.