0h 44min, feb 28, 1953 y - Francis and Crick
On February 28, 1953, Francis and Crick helped discover that DNA is double stranded. Watson and Crick took a crucial conceptual step, suggesting the molecule was made of two chains of nucleotides, each in a helix as Franklin had found, but one going up and the other going down. Crick had just learned of Chargaff's findings about base pairs in the summer of 1952. He added that to the model, so that matching base pairs interlocked in the middle of the double helix to keep the distance between the chains constant. Watson and Crick showed that each strand of the DNA molecule was a template for the other. During cell division the two strands separate and on each strand a new "other half" is built, just like the one before. This way DNA can reproduce itself without changing its structure -- except for occasional errors, or mutations.
Added to timeline:
Mrs. Grogan's Project (May have to scroll to the 1800s)