Download Virus - Duplin County Schools

What is a virus?
• Tiny organisms that may lead to mild to severe
illnesses in humans, animals, and plants
How big are viruses?
• 100 times smaller than a single bacteria cell
• bacteria cell is 10 times smaller than a human
cell
• human cell 10 times smaller that the diameter
of a single human hair
Are viruses alive?
• Viruses by themselves are not alive. They
cannot grow or multiply on their own and
need to enter a human or animal cell and take
over the cell to help them multiply.
• May also infect bacterial cells
• The virus particle or the virions attack the cell
and take over its machinery to carry out their
own life processes of multiplication and
growth. An infected cell will produce viral
particles instead of its usual products.
Structure of a virus
A virion (virus particle) has three main parts:
• Nucleic acid – this is the core of the virus with the
DNA or RNA. The DNA or RNA holds all of the
information for the virus and that makes it
unique and helps it multiply.
• Protein Coat (capsid) – This is covering over the
nucleic acid that protects it.
• Lipid membrane (envelope) – this covers the
capsid. Many viruses do not have this envelope
and are called naked viruses.
How do viruses infect?
• Viruses do not have the chemical machinery
needed to survive on their own. They, thus
seek out host cells in which they can multiply.
These viruses enter the body from the
environment or other individuals from soil to
water to air via nose, mouth, or any breaks in
the skin and seek a cell to infect.
Life cycle of a basic virus
There are a few basic steps that all infecting viruses follow and
these are called the lytic cycle. These include:
• A virus particle attaches to a host cell (process of
adsorption)
• The particle injects its DNA or RNA into the host cell (entry)
• The invading DNA or RNA takes over the cell and recruits
the host’s enzymes
• The cellular enzymes start making new virus particles
(replication)
• The particles of the virus created by the cell come together
to form new viruses (assembly)
• The newly formed viruses kill the cell so that they may
break free and search for a new host cell (release)
How a virus enters your body
• http://www.youtube.com/watch?feature=play
er_embedded&v=Rpj0emEGShQ