Evolution and Genetic Engineering - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 717

2. Electroporationd Cells are subjected to a high-voltage pulse, which temporarily disrupts
the membrane and allows the vector to enter the cell. This is the most efficient method of
delivering genes to bacterial cells.
3. Virusesd The vector is first incorporated into a virus, which is then used to infect cells,
carrying the foreign gene along with its own genetic material. Since viruses rely on getting
their DNA into host cells for their survival, they have evolved many successful methods
and so are an obvious choice for gene delivery. The virus must first be genetically
engineered to make it safe, so that it cannot reproduce itself or make toxins. Three viruses
are commonly used:

Bacteriophages (or phages) are viruses that infect bacteria. They are a very effective way of
delivering large genes into bacterial cells in culture.
Adenoviruses are human viruses that cause respiratory diseases including the common
cold. Their genetic material is double-stranded DNA, and they are ideal for delivering
genes to living patients in gene therapy. Their DNA is not incorporated into the host's
chromosomes, so it is not replicated, but their genes are expressed ( Fig. 14.11 ).

4. Gene gund This extraordinary technique fires microscopic gold particles coated with the
foreign DNA at the cells using a compressed air gun. It is designed to overcome the
problem of the strong cell wall in plant tissue, since the particles can penetrate the cell wall
and the cell and nuclear membranes and deliver the DNA to the nucleus, where it is
sometimes expressed.

nucleus nucleus

Core and DNA release into nucleus and/or
ribosome

adenovirus Virus attaches to membrane and enters by endocytosis

nucleus
Viral DNA is replicated and translated by
host ribosome

nucleus

New viruses assembled and host cell
membrane ruptures, killing host cell

FIGURE 14.11 Replication of adenovirus.