The study of viruses is called virology.
Viruses aren't classified in the traditional sense, because they are on the border of living and non-living.
Not living: They are not cells and they cannot metabolize
Living: They can reproduces (but they need the help of a host cell!!)
Since they only show life functions in a host cell, we call them obligate parasites.
Structure
20-300nm large
inner core of nucleic acid (DNA or RNA)
outer protein coat (aka capsid) - exist in a variety of shapes (cylindrical, spherical, polyhedral, etc)
viral envelope (sometimes)
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Grouping (or classification) is based on viral shape, kind of nucleic acid and the host that is affected
Replication (Lytic cycle)
1. ATTACHMENT: recognizes and attaches to receptor site on cell membrane.
2. ENTRY: sometimes just the nucleic acid is "injected" into the cell, sometimes the whole virus enters the cell.
3. REPLICATION: reprograms host cell to produce capsids and viral nucleic acids
4. FORMATION: nucleic acids and capsids are assembled.
5. LYSIS and RELEASE: the host cell bursts and releases new viruses into the environment.
Virulent viruses kill host cells.
Temperate viruses don't kill immediately: their nucleic acid builds into the host's nucleic acids and replicates with the host's DNA. Something triggers the virus to become virulent and then it enters the lytic cycle. HIV and herpes are these kind of viruses.
Viruses are NOT killed by antibiotics
VACCINES can prevent some viral diseases and help to prevent epidemics (jarvany)
Examples of viral diseases: influenza, rubeola, measles (kanyaro), tick-born encephalitis, hepatitis, rabies, polio, smallpox, chicken pox
Viroids and Prions (weird stuff!)
Viroids are short, single-stranded RNA, with no capsid. They infect plants (eg. potato, coconut, etc) causing virus-like symptoms.
Prions are glycoproteins which are capable of reproducing in mammal cells, even though they have no nucleic acids! They cause diseases like kuru and BSE (bovine spongiform encephalopathy)
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