Viral DNA and RNA can infect the nucleus. If
a cell is like a factory, the nucleus is like
the main office. It gives instructions on what
to make. The virus takes over the main office,
cancelling the normal instructions and telling
the workers to make viruses.
This may seem like a perfect plan, but
individuals have ways of protecting themselves
when their own cells go bad. People (and many
other animals like us) have immune systems that
recognize “bad” cells. Each cell has a sort of
ID tag. This tells the immune system, “I belong
If we go back to the story of the factory,
imagine that the factory workers have to post a
sort of flag each day so that the police know
everything is okay. The criminals who take over
the factory don’t know how to post the flag the
right way. When the police see the flag posted,
they attack the factory. Our factory story
stops making sense here, because the immune
system can only get rid of the viruses by
completely destroying the cell. They do poke
holes in the outer covering or membrane. Once
the stuff inside the cell can mix with the stuff
outside the cell, the cell dies.
The RNA in a virus looks a lot like our RNA.
It is in strands or strings. One difference is
that our RNA is always in single strings, while
viruses may have a double strand of RNA. Our
DNA is in much longer double strings that are
wrapped around proteins. The Viral DNA can have
different shapes. It is usually much shorter.
It might be in double strings wrapped around
proteins, or in double rings without proteins,
or some other shape. Some viruses have no DNA.
They only have RNA.
Do you think viruses are alive? How would
you decide whether they are alive or not?
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