What is a virus



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.

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