53 
Slide 15 
Experiments with Eukaryotic Host-Vector Systems 
Extrachromosomal 
organelle DNA 
(mitochondria, 
chlorop lasts) 
Vectors 
Host cells 
— Eukaryotic origin 
— grown as single cells 
— fragile and fastidious 
— unable to escape in viable form 
o 
Viral DNA 
We will talk first about animal cells. These host cells might typi- 
cally be derived from hamsters, mice, monkeys, or humans. The cells them- 
selves are fragile and fastidious, as is well-known by anyone who has spent 
time trying to grown them. There is little or no chance that a living cell 
could escape from a laboratory in the way that _E. coli might. Therefore, 
the containment considerations focus on the virus. 
Animal viruses can, of course, be carried out of laboratories and can 
be spread if laboratory workers become infected. As shown in the diagram 
at the bottom, these viruses, like the bacteriophage, are composed of a DNA 
molecule, shown here as a circle, the largest circle, encased in a protein 
coat shown by the small circles. The virus itself, as well as the isolated 
DNA can enter and infect cells. 
May I have the next slide (16), please? 
As with the bacteriophage, several alternative situations may result 
upon infection of animal cells with animal viruses or viral DNA. The virus 
or viral DNA may enter the cell, use the cell as a factory for producing 
more viral DNA and protein, and finally, new viral particles may be released 
from a destroyed cell. 
Alternatively, the viral DNA may become joined to the original chromo- 
somal DNA of the host cell, and thereby be passed to every offspring of the 
cell in a process which is called transformation. 
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