Nucleic acids.

Nucleic acids were discovered in the mid-nineteenth century, but their role as genetic material was not substantiated until the mid-twentieth century. When chromosomes were discovered at the beginning of the twentieth century, they were quickly identified as the genetic material of the cell. Chromosomes were found to be composed of nucleic acids and proteins. Through the experiments of Fred Griffith on transformation in pneumonia bacteria and the work of Alfred Hershey and Martha Chase on bacteriophages, by 1952 most biologists recognized deoxyribonucleic acid (DNA) as containing the genes. James Watson and Francis Crick provided the capstone to science’s initial understanding of nucleic acids when they determined the double helix structure of DNA in 1953.