Final answer:
James Watson and Francis Crick believed that the structure of DNA is a double helix formed by two polynucleotide chains. They pieced together the DNA molecule based on data from Rosalind Franklin and Maurice Wilkins.
Step-by-step explanation:
James Watson and Francis Crick proposed that the structure of DNA consists of two side-by-side polynucleotide chains wrapped into the shape of a double helix.
In the 1950s, Watson and Crick worked together at the University of Cambridge, England, to determine the structure of DNA. They were able to piece together the puzzle of the DNA molecule based on data from Rosalind Franklin and Maurice Wilkins, who were also studying DNA structure using X-ray diffraction methods.
Watson and Crick's model of the DNA double helix, which they built in 1953, is displayed at the Science Museum in London.