 James Watson and Francis Crick determined the structure of DNA in 1953 , using the X @-@ ray crystallography work of Rosalind Franklin and Maurice Wilkins that indicated DNA had a helical structure ( i.e. , shaped like a corkscrew ) . Their double @-@ helix model had two strands of DNA with the nucleotides pointing inward , each matching a complementary nucleotide on the other strand to form what looks like rungs on a twisted ladder . This structure showed that genetic information exists in the sequence of nucleotides on each strand of DNA . The structure also suggested a simple method for replication : if the strands are separated , new partner strands can be reconstructed for each based on the sequence of the old strand . This property is what gives DNA its semi @-@ conservative nature where one strand of new DNA is from an original parent strand . 
