DNA contains the genetic instructions that determine traits in living organisms. It is made up of two strands coiled into a spiral ladder shape. The sides of the DNA ladder consist of alternating sugar and phosphate molecules, while the rungs consist of pairs of nitrogen bases - adenine pairs with thymine and cytosine pairs with guanine. DNA nucleotides each contain a phosphate, sugar (deoxyribose), and one of four nitrogen bases (adenine, thymine, cytosine, or guanine) that form base pairs between the two DNA strands.