What Is Biotechnology? - Biotechnology and Your Health: Pharmaceutical Applications - page 14

their membranes, the proteins wrapped around their DNA to protect
and control which proteins are made from its instructions, the enzyme
proteins that transform raw food materials into energy to keep the cell
alive, and the proteins needed to build a new cell when one cell divides
into two. Eukaryotic cells , cells that have a nucleus, must also make the
proteins for the membrane of their nucleus , the sack containing
their genetic material, with its proteins split into the bits called
chromosomes. Eukaryotic cells of all sorts—yeast, plant, animal,
and human—make the proteins for their little energy factories called
mitochondria , and plant cells make the proteins for the chloroplasts ,
the energy factories that capture light and transform it into chemi-
cal energy so the plant cell can make proteins and carbohydrates. In
complex creatures like animals, plants, insects, and even some worms
with many different kinds of cells, the cells are unique because they
make different proteins. To make a simple comparison, liver cells
make proteins to help break down food, but liver cells do not grow
hair. The cells that grow hair make different proteins.
Choosing Which Cell to Engineer
Genetic engineers must decide into which cell they will insert their
gene—a choice that depends on the protein product, its intended
use, and costs. Bacterial cells are less expensive to grow in large
numbers for production of a protein, but as we shall see, human and
other eukaryotic cells, unlike bacterial cells, attach sugar molecules
to the proteins they make, and this difference may be important for
how the body handles a protein or for how well the protein works.
It is expensive to grow large numbers of human or animal cells
to manufacture a protein, and it may be tricky. Small changes in
growing conditions—such as temperature, acidity of the broth, and
vitamins or hormones in the broth—may change the size, shape, or
amount of the protein made by the cells. Researchers are exploring
the use of insect cells to produce protein drugs and the use of
viruses that infect insect cells as vectors.