5 Greatest Scientific Discoveries of 20th Century?
                 These are my opinion... What's your opinion.
                 Do you have any related to Cell & Molecular Biology?

1.   Theory of Relativity Albert Einstein 1905
if speed of light is a constant , then time & motion are relative to the observer, 
             and mass and energy are equivalent
E = mc2   
2.   Atomic Structure & Fission 1911-1938 
             1911 Rutherford discovers atomic particles; 
   1938 Otto
Hahn & Fritz Strassman split nucleus of atom releasing energy [fission]
3.   Structure of DNA: J.D. Watson & Francis Crick  1953 
   double helical polynucleotide of
4.   Greenhouse Effect Global Warming   1970  
       awakens us to science of environmental preservation -
NOVA site 
5.   Comet Shoemaker-Levy hits Jupiter   1994  
    March 1993 Gene & Carolyn Shoemaker discover comet – 
                     collides with Jupiter*...  offers suggestions on how
LIFE might have begun 
via organic molecule seeding and water dumping by comets