1953 James Watson and Francis Crick determine the molecular structure of DNA. Two strands of DNA wind around one another in a double helix. The nucleotide bases-A, T, G, and C-run down the center of the helix, the A from one strand always pairing with a T on the other; the Gs pairing with Cs. This arrangement-the pairing of complementary bases-allows DNA to be copied. It also allows the pairing of matching sequences on DNA chips. In 1962, Watson and Crick take home a Nobel prize for their efforts.