What is a virus?
A. It is a nonliving strand of genetic material surrounded by a protein coat, known as the
capsid.
i. Either DNA or RNA as the core, but never both
B. Viruses are considered nonliving:
a. They are not composed of cells.
b. They cannot reproduce independently (require a host).
C. Causes disease, which is a change other than an injury that disrupts the normal
functions of the body.
a. Can be caused by microorganisms (bacteria, viruses, protists). This is known
as the germ theory of infectious disease.
b. Most viruses have DNA as the core (herpes, chicken pox, flu, rabies, polio,
smallpox etc)
c. Specific to what they infect= they have target areas. Ex: a stomach virus that is
inhaled will not infect a person.
Viruses are grouped into three main categories depending on what they do (how they infect):
A. Oncogenic virus: cause cancer, for example HPV
B. Retroviruses: viruses composed of RNA. These infect the host’s genetic information
and translate their RNA into the host’s DNA (so it works backwards), combining its
code with that of the host. Examples: HIV
C. Prions: are protein infection particles. Example: mad cow
How do viruses infect your cells? Major difference, one waits and one destroys
A. Lytic infection: the virus infects the cell by injecting its DNA. It then programs the cell
to replicate the viral DNA repeatedly, until it causes the cell to burst. The new viruses
then repeat the cycle with a new host cell.
B. Lysogenic infection: the virus does not lyse (break open) the host immediately, but
instead of taking over the host’s DNA it combines its DNA with the host. As the host
cell replicates and divides it will pass on the viral DNA to the identical daughter cells.
The virus will remain dormant until something triggers it to go into the lytic cycle.
Vaccines are prepared
weakened or killed (torn
apart) virus or viral proteins
that you receive to build up
your immunity. In theory
when you come into contact
with the virus after
vaccination, your antibodies
will recognize it and attack it –
so you should not get sick.