What is the significance of Franklin's X-ray diffraction photograph of DNA?

Franklin's X-ray diffraction photograph of DNA is pivotal because it provided crucial evidence that contributed to the understanding of the DNA structure. This particular photograph, often referred to as Photograph 51, displayed a distinctive pattern that indicated DNA had a helical structure. The cross-like pattern observed in the diffraction image suggested that DNA was not a simple strand but rather a double helix. This insight laid the groundwork for Watson and Crick's later model of DNA, which proposed the double helical structure as consisting of two strands coiled around each other. The significance of this finding cannot be overstated, as it was foundational in elucidating how genetic information is stored and transmitted within cells.

In contrast, the other options do not accurately reflect the importance of Franklin's work. The replication of DNA is a process that would be studied later, and although protein structure is an important biological topic, it is unrelated to Franklin's work on DNA. Lastly, RNA's structure was a separate discovery and not relevant to Franklin's X-ray diffraction studies.