Types of Recombinant Drugs - Biotechnology and Your Health: Pharmaceutical Applications - page 48

as well as the type that grows naturally in our intestines. Industrial
E. coli have been genetically changed so they cannot grow outside of
a carefully controlled laboratory setting and cannot cause disease.
Changing the Bacterium's DNA
Biotechnology uses a series of techniques to harness a bacterium's
ability to increase quickly to very large numbers in a solution of
inexpensive chemicals, and to produce large amounts of protein.
With the toolbox of recombinant DNA technology, the genetic mate-
rial of the bacterium is changed through the addition of a segment
of DNA that carries instructions for the protein that will become a
drug; in this case, human insulin. Each bacterium becomes a very
small production “factory” for the protein that is then purified, or
freed from all the other chemicals.
Changing the Protein
Other steps may be needed to actually make the protein useful. For
example, the protein may need to be treated to make it on take the
correct shape, or to make it fold the right way (Figure 4.2). In the
case of insulin, something else is needed, something that is not
required to make pig or cow insulin useful for humans. When the
islet of Langerhans cells in the pancreas of cows, pigs, or humans
“read” the gene for insulin to create a protein, the first product is a
large protein. The starting protein is trimmed of a precise section of
amino acids while it travels in the islet cell to the spot where it will
be packaged for transport into the bloodstream. In that package, the
protein is again clipped at two spots with great precision to produce
insulin. Insulin consists of two short peptides , one of which is 21
amino acids long and the other 30 amino acids long. The peptides
are held together by weak chemical bonds. To produce insulin in
E. coli , scientists knew that the bacteria could not process the starting
protein into insulin on their own, so they came up with a solution.
They inserted two different plasmids into E. coli , one carrying the