E. coli here is a host cell.
In respect to this procedure, two things were used to carry out the process of human insulin production, namely a host and a vector.
In molecular cloning, a vector is a DNA molecule used as a vehicle to artificially carry foreign genetic material into another cell. In the production of human insulin, the vector in this case was a plasmid, a small circular double stranded DNA found in most bacteria, that is distinct from the cell's chromosomal DNA.
This circular DNA is removed from the bacteria, cut open and DNA for producing insulin is inserted into it then it is closed into a ring again. This recombinant DNA plasmid is then inserted into a host cell, such as E.coli which then makes the insulin protein together with its own proteins.
