DNA sequencing 1953, James Watson and Francis Crick put forward their double-helix model of DNA, based on crystallized X-ray structures being studied by Rosalind Franklin – and without crediting her. According to the model, DNA is composed of two strands of nucleotides coiled around each other, linked together by hydrogen bonds and running in opposite directions. Each strand is composed of four complementary nucleotides – adenine (A), cytosine (C), guanine (G) and thymine (T) – with an A on one strand always paired with T on the other, and C always paired with G. They proposed such a structure allowed each strand
Rosalind Franklin and DNA was a general consensus at the time that they were at the inside); and the other is that DNA exists in two forms, a crystalline (dry form) A-DNA and a hydrated (wet form) B-DNA. With her PhD student Raymond Gosling, she produced a series of X-ray images of DNA. The photograph (number 51, hence, popularised as Photo 51) of B-DNA taken in May 1952 was especially crucial. X-ray crystallography did not immediately show the precise helical structure. Franklin chose to work on A-DNA, while B-DNA was given to Maurice Wilkins. By the early 1953, Franklin was aware that both A