In the early 1950s, American biologist James Watson and British physicist Francis Crick came up with their famous model of the DNA double helix. The structure of DNA, as represented in Watson and Crick's model, is a double-stranded helix. The sugar-phosphate backbones of the DNA strands make up the outside of the helix, while the nitrogenous bases are found on the inside and form hydrogen-bonded pairs that hold the DNA strands together. Other topics covered include DNA replication, RNA transcription, and RNA translation. Part of the "Biology" series.