Virus

Infectious unit usually 17-300nm diameter (excluding mega viruses; smallest – Porcine Circovirus 17nm, largest – probably Pithovirus sibericum 1500 nm), composed of nucleic acid (either DNA or RNA), protein and in some cases an outer lipid layer caller envelope. The virus does not possess mechanisms to generate their energy or synthesise protein/structural components on its own. They infect a host cell and use the cell resources to reproduce/replicate as intracellular parasites.

Virus structure:

Virus, unlike bacteria and higher organisms, possess one type of nucleic acid at its core – DNA or RNA. DNA or RNA could be double-stranded or single-stranded, positive or negative sense. The nucleic acid is covered by a protein covering called the capsid. The capsid and the nucleic acid together is called a nucleocapsid.

The nucleocapsid, in some virus, is covered by a lipid bilayer, derived from the cell membrane. Presence of the envelope makes the virus susceptible to the detergents and solvents, like alcohol. 

Protein and glycoprotein could be embedded on the envelope, which imparts various properties to the virus.
In some viruses like herpesvirus, a protein layer exists between the envelope and the capsid, called tegument.

The Nucleocapsid may have an icosahedral, helical or a complex symmetry. In some viruses like
Hepatitis D, the symmetry is not determined.

Icosahedral symmetry:

Helical symmetry:

File:Helical capsid.jpg - Wikimedia Commons

Complex structure:


Poxvirus (Stanford.edu)

Icosahedral symmetry

FamilyGenusEnvelopeNucleic acid
Parvoviridae

PartetravirusParvovirus 4
ErythrovirusParvovirus B19
BocavirusHuman Bocavirus
DependovirusAdeno-associated viruses

 

NossDNA;
linear
Herpesviridae

AlphaherpesvirinaeHerpes simplex viruses,
varicella-zoster virus
BetaherpesvirinaeCMV
HHV6
GammaherpesvirusEBV
HHV8

 

YesdsDNA;
linear
Adenoviridae

MastadenovirusHuman adenovirus

 

NodsDNA;
linear
Papillomaviridae

PapillomavirusHuman papillomavirus

 

NodsDNA;
circular
Polyomaviridae

PolyomavirusBK, JC, KI, WU,
Merkel cell polyoma virus.

 

NodsDNA;
circular
Hepadnaviridae

OrthohepadnavirusHepatitis B virus

 

Yespartially dsDNA;
circular
Retroviridae
(Also considered
spherical capsid/
cone-shaped
symmetry by some) 

OrthoretrovirusHervK, Erv-3, S71
HTLV 1-3 (deltaretrovirus)
HIV 1-2 (lentivirus)
Spumaretrovirus

 

Yes(+)ssRNA;
linear,
Transcript
to dsDNA.
Reoviridae

OrthoreovirusReovirus
RotavirusRotavirus
ColtivirusColorado tick fever virus

 

NodsRNA,
linear,
10-12 segments
BirnaviridaeNodsRNA,
linear,
2 segments
Togaviridae

AlphavirusSemliki Forest virus,
Chikungunya virus,
O’nyong-nyong virus,
Ross River virus
RubivirusRubella virus

 

Yes(+)ssRNA,
linear
Flaviviridae
(Some consider
it to have spherical
symmetry)

FlavivirusYellow fever virus,
dengue virus,
West Nile virus,
tickborne encephalitis virus
HepacivirusHepatitis C virus

 

Yes(+)ssRNA;
linear
Hepeviridae

HepevirusHepatitis E virus

 

No(+)ssRNA
linear
Caliciviridae

NorovirusNorwalk virus
SapovirusSapporovirus

 

No(+)ssRNA,
linear
Astroviridae

MamastrovirusHuman astrovirus

 

No(+)ssRNA,
linear
Picornaviridae

EnterovirusPoliovirus,
coxsackievirus,
human enteroviruses,
human rhinoviruses
ApthovirusFoot and mouth disease virus
ParechovirusParechovirus
HepatovirusHepatitis A virus

 

No(+)ssRNA,
linear

Helical symmetry:

FamilyGenusEnvelopeNucleic acid
Coronaviridae

AlphacoronavirusHuman coronaviruses 229E
Human coronaviruses NL63
BetacoronavirusHuman coronavirus OC43
Human coronavirus HKU1
SARS-associated coronavirus
TorovirusHuman torovirus

 

Yes(+)ssRNA,
linear
Rhabdoviridae

LyssavirusRabies virus

 

Yes(-)ssRNA,
linear
Bornaviridae

Bornavirus

 

Yes(-)ssRNA,
linear
Paramyxoviridae

RespirovirusParainfluenza virus
RubulavirusMumps
AvulavirusNewcastle disease virus
MorbillivirusMeasles virus
HenipavirusHendra virus, Nipah virus
PneumovirusRespiratory syncytial virus
MetapneumovirusHuman metapneumovirus

 

Yes(-)ssRNA,
linear
Filoviridae

MarburgvirusMarburgvirus
EbolavirusEbolavirus

 

Yes(-)ssRNA,
linear
Arenaviridae
(Some consider
it to have
spherical
symmetry)

ArenavirusLCMV, Lassa, Lujo,
Junin, Machupo, Guanarito,
Chapare, Tacaribe, Sabia

 

Yes(- or ambisense)
ssRNA
linear,
2 segments
Bunyaviridae

OrthobunyavirusCalifornia encephalitis virus
PhlebovirusRift Valley fever virus,
sandfly fever virus
NairovirusCrimean-Congo fever virus
HantavirusHantaan virus, Puumala virus,
Sin Nombre virus

 

Yes(- or ambisense)
ssRNA
linear,
3 segments
Orthomyxoviridae

Influenza virusInfluenza A, B, C

 

Yes(-)ssRNA
linear,
7-8 segments

Complex nucleocapsid:

FamilyGenusEnvelopeNucleic acid
Poxviridae

OrthopoxvirusVariola viruses,
vaccinia virus
ParapoxvirusOrf virus
MolluscipoxvirusMolluscum contagiosum virus
YatapoxvirusTanapox virus,
Yaba monkey tumour virus

YesdsDNA;
linear
Asfarviridae

AsfivirusAfrican swine fever virus

YesdsDNA;
linear;

Bacteriophage has a complex nucleocapsid structure.

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