RNA Viralology - Just the Basics, please!

Remember:  Viruses are 1) Energy-less.  They
float around until they come in contact with an appropriate cell   2) They are
basic life forms composed of protein coat, called a capsid that
surrounds genetic material.   3) The genetic material is either
DNA or RNA.  Never Both!!   4)
Replication of the genetic material occurs when the virus takes control of the
host cell's synthetic machine.

RNA (There are 3
types)
1. Positive (+) stranded
2. Negative (-) stranded
3.
Retroviruses

Viral Family	Envelope	RNA Structure	Capsid Symmetry	Medical Importance
Piconavirus	NO	SS + Linear	Icosahedral	"PERCH on a Peako" Poliovirus - Salk/Savin - IPV/OPV Echovirus - aseptic meningitis Rhinovirus - "Common cold" Coxsackievirus - aseptic meningitis, herpangina - febrile pharyngtis, hand/foot/mouth dx, myocarditis Hav - acute viral hepatitis
Calicivaruses	NO	SS + Linear	Icosahedral	HEV Norwalk - viral gastroenteritis, cruises
Reoviruses	No	DS linear, segmented	Icosahedral	Reovirus - colorado tick fever Rotavirus - #1 cause of fatal diarrhea in children R.O.T.A. - "Right Out The Anus"
Flavivirus	Yes	SS + Linear	Icosahedral	HCV Yellow Fever Dengue St. Louis encephalitis West Nile Virus
Togaviruses	Yes	SS + Linear	Icosahedral	Rubella (German measles) - descending rash Eastern Equine encephalitis Western Equine encephalitis
Retroviruses	Yes	SS + Linear	Icosahedral	Have Reverse transcriptase HIV - AIDS HTLV - T-cell leukemia

Coronaviruses	yes	SS + Linear	Helical	Coronavirus - "common cold" & SARS
Orthomyxoviruses	Yes	SS, -, linear segmented	helical	Influenenza Orthomyxovirus - Ordinary flu
Paramyxoviruses	yes	SS, -, linear nonsegmented	helical	PaRaMyxovirus: Parainfluenza - croup RSV - bronciolitis in babies, Rx-ribavarin Measles Mumps PARAmyxovirus - PARAde of viruses
Rhabdoviruses	yes	SS -, linear	Helical	Rabies
Filoviruses	yes	SS - , linear	helical	Ebola/Marburg hemorrhagic fever, often fatal
Arenaviruses	Yes	SS - , circular	helical	LCV - lymphocytic choriomeningitis Menengitis - spread by mice
Bunyaviruses	yes	SS, -, circular	Helical	California encephalitis Sandfly/Rift valley fevers Crimean-Congo hemorrhagic fever Hantavirus - hemorrhagic fever, pneumonia
Deltavirus	Yes	SS, - , circular	Helical	HDV
Table adapted from FirstAid USMLE Step 1		SS = single stranded DS = double stranded + = positive polarity - = negative polarity

1.  The POSITIVE (+) means that the RNA is
just like a messenger RNA (mRNA).  When a positive RNA virus enters a cell, its
RNA acts positively and immediately can be translated by the host's ribosomes
into protein. 

2.  Negative (-) stranded RNA viruses enter a cell, they are not able to begin translation immediately.  They must 1st get rid of their negative attitude and become POSITIVE (+) (like mRNA). 

• To do this, Neg. viruses must carry , in their capsid, an enzyme called RNA-dependent RNA polymerase, which will carry out the transcription of the negative strand to positive strand. 
  
• Human cells do not have RNA-dependent RNA polymerase!, so (-) viruses must carry their own negative attitude enzyme with them.

3.  One special RNA virus deserves mention here (RETROVIRUSES) The RNA of the retroviruses is transcribed in a reverse fashion into DNA.  So, to do this, they require Reverse Transcriptase.

For a different way to learn the viruses, check out the virus stories below.  Once you've drawn it out, written in your own notes and taught it to someone else, it IS yours!