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Unit 1 Viruses and Bacteria
Bacteria and viruses also differ greatly in their methods of
reproduction. Again, it is the bacterium's status as a single-celled living
organism that sets it apart from the virus. Bacteria reproduce asexually
through cell division. Once they grow to a certain size, the DNA inside
splits into two identical structures, and slowly the cell breaks apart, with
one group of DNA in each new cell. Reproduction of bacteria is limited,
however, to the nutrients available in the environment. Viruses, on the
other hand, cannot reproduce until they have latched onto a host. After a
virus attaches itself to a host cell, the virus works its way into the cell
through the membrane. As the virus's protein shell dissolves, the genetic
information in the virus is released into the cell where it can reproduce
and spread. Viruses will continue to reproduce rapidly until the host's
resources have been completely used up, at which time they can simply
find a new host.
[A] Diseases caused by viruses range from the common cold to HIV,
and can be either temporary and relatively harmless or life-long and
potentially deadly. [B] While there is no real cure for viral diseases,
vaccines and antiviral drugs can help. [C] Vaccines introduce a very small
portion of the virus into the body, so that if a person does come in
contact with the virus, he or she is already immune to its effects. [D]
Antiviral drugs have only come into being in the last 20 years or so, and
work by halting the reproduction of the virus rather than killing it.
Bacterial infections are far easier to treat; antibiotic drugs work with the
immune system to quickly kill most infections.
-6-
Bacteria and viruses also differ greatly in their methods of
reproduction. Again, it is the bacterium's status as a single-celled living
organism that sets it apart from the virus. Bacteria reproduce asexually
through cell division. Once they grow to a certain size, the DNA inside
splits into two identical structures, and slowly the cell breaks apart, with
one group of DNA in each new cell. Reproduction of bacteria is limited,
however, to the nutrients available in the environment. Viruses, on the
other hand, cannot reproduce until they have latched onto a host. After a
virus attaches itself to a host cell, the virus works its way into the cell
through the membrane. As the virus's protein shell dissolves, the genetic
information in the virus is released into the cell where it can reproduce
and spread. Viruses will continue to reproduce rapidly until the host's
resources have been completely used up, at which time they can simply
find a new host.
[A] Diseases caused by viruses range from the common cold to HIV,
and can be either temporary and relatively harmless or life-long and
potentially deadly. [B] While there is no real cure for viral diseases,
vaccines and antiviral drugs can help. [C] Vaccines introduce a very small
portion of the virus into the body, so that if a person does come in
contact with the virus, he or she is already immune to its effects. [D]
Antiviral drugs have only come into being in the last 20 years or so, and
work by halting the reproduction of the virus rather than killing it.
Bacterial infections are far easier to treat; antibiotic drugs work with the
immune system to quickly kill most infections.
-6-
