Decoding human DNA (2nd part)
Fred Sangar decoded the genome of a tiny virus: phi x 174
This virus is so small that it can even be infected by bacteria. That's why it's called a bacteriophage. It has 5400 nucleotides. These nucleotides can be A, C, G, or T. This bacteriophage also has the property that it multiplies optimally in a Petri dish.
To copy the DNA of this bacteriophage, Sanger used a chemical that could stop the replication process randomly if a certain nucleotide appeared. For example, in the phi x 174 genome, Adenine often appeared at the top of a sequence in different lengths. He was then able to compare them.
To clearly split the nucleotides, he used a process called electrophoresis.
It is a device where you can spread the nucleotides and then release a gel over them (see bottom picture on the left). Through the gel, the nucleotides are separated according to their length. Sangar used this method because he knew that small molecules move quickly when you send an electric current through them.
Large molecules then move much slower.
