Two scientists, Max and Gunther, proposed a paper with three different methods of DNA replication. First they explained semi-conservative replication, which is a daughter strand that contains one strand from the parent and the other is newly formed. The second was conservative replication which theorized a new double helix strand being created in the first generation. Third they described dispersive DNA replication where both a new and old strand break and separate. It was known that DNA can be copied; but scientists could not understand which of these methods took place. Watson and Crick wrote an article about DNA replication and how it would separate forming two chains as semi-conservative replication. The two scientists, Matthew Meselson and Franklin Stahl, discussed a method to test this theory of semi-conservative replication.
DNA is a three dimensional structure that carries hereditary information, each strand has nucleotides containing a base, sugar, and phosphate. The four chemical bases always pair in the same way; adenine joins to thymine (A&T) and cytosine joins guanine (C&G). The Meselsen-Stahl experiment was based on reactions with heavy isotopes of nitrogen in order to identify the new and old DNA strand. Nitrogen’s atomic mass number is 14 which means that it contains 7 protons and 7 neutrons. Heavy isotopes have an extra neutron which makes it heavier and it’s called 15N.
In their experiment they grew E. coli (bacteria) on a medium containing heavy