Download What is a virus

Structure
- genetic material (Either DNA or RNA, but never both)
- Capsid- a protein coat that surrounds the genetic material
Why are viruses considered nonliving?
- They are not composed of cells.
- They cannot reproduce independently (require a host).
Can cause disease
- Germ theory of infectious disease- disease can be caused by microorganisms
(bacteria, viruses, protists).
- Examples with DNA: herpes, chicken pox, flu, rabies, polio, smallpox
- Specific to what they infect= they have target areas. Ex: a stomach virus that is
inhaled will not infect a person.
Other types of viruses
1. Oncogenic virus- cause cancer. Example= HPV (Human Papillomavirus)
2. 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. Example= HIV
3. Prions- protein infection particles. Example= Mad Cow
Virus Cycles
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.
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- weakened or killed
(torn apart) virus or viral
proteins that you receive to
build up your immunity.
- The vaccine exposes
you to the virus so your
immune system will build
up antibodies.
- When you come into
contact with the virus
after vaccination, your
antibodies will recognize
it and attack it – so you
should not get sick.