Final answer:
In the late 19th century, scientists discovered nucleic acids, which were later identified as RNA and DNA. The structure of DNA was determined in the 1950s by Watson and Crick.
Step-by-step explanation:
In the late 19th century, scientists made significant discoveries about DNA and RNA. Friedrich Miescher was the first to isolate nucleic acids from white blood cells, which were later named RNA and DNA. This laid the foundation for the understanding of DNA's role as the genetic material. It wasn't until the 1950s that the structure of DNA was determined by Watson and Crick.