Which of the following did watson and crick already know when they were trying to determine the structure of dna? the number of which of the following did watson and crick already know when they were trying to determine the structure of dna? the number of guanines is always the same as thymines pyrimidines is always larger than purines cytosines is always the same as adenines purines is always larger than the number of pyrimidines purines is always the same as pyrimidines

Watson and Crick already knew that the number of purines is always the same as pyrimidines.

The scientists that contribute to discovery of DNA and its complete structure:

•  Friedrich Miescher-was the first who found DNA inside the nucleus (first it was called nuclein) while he was trying to discover the protein components of leukocytes (1869)

•Phoebus Levene- was the first who discovered three major components of a nucleotide (1919)

•Erwin Chargaff –discovered that the total amount of purines (A + G) and the total amount of pyrimidines (C + T) are nearly equal (Chargaff’s rule) (1950)

•Rosalind Franklin and Maurice Wilkins, did an important X-ray crystallography work that contributed to Watson and Crick's discovery of double-helical model for the structure of DNA.