Final answer:
James Watson and Francis Crick used Rosalind Franklin's X-ray diffraction images along with Chargaff's rules to propose a double helical DNA structure, which they published in Nature in 1953. Their DNA model described two strands of nucleotide chains bound by complementary base pairing, leading to the form of a double helix.
Step-by-step explanation:
James Watson and Francis Crick proposed that the structure of DNA is a double helix, a model they built using data from a variety of sources, including Rosalind Franklin's X-ray diffraction images. Franklin's images, displaying the X-ray diffraction pattern of DNA, were crucial in revealing its helical nature.
Watson and Crick used these images and Chargaff's rules to piece toghether the idea that DNA is composed of two antiparallel nucleic acid chains held together by complementary base pairing, forming the now-famous double helix shape, resembling a spiral staircase with bases as the steps. In their landmark paper published in Nature in 1953, they discussed this structure along with a mechanism for DNA replication, because of the specificity of base pairing.
In April 1953, Watson and Crick published their model in Nature, which was subsequently confirmed by further research, such as that of Alexander Rich. Unfortunately, even though Franklin's contribution was significant, she had passed away by the time the Nobel Prize was awarded to Watson, Crick, and Maurice Wilkins in 1962, and at that time the Nobel Prize was not awarded posthumously.