Download Viruses

Viruses
http://www.bing.com/images/sear
ch?q=virus&view=detail&id=5AD6
2840C81847683B7591AEC1F651E
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What is a virus?

Characteristics
◦ Infectious agent
◦ Contains nucleic acids within a
protein capsid
◦ May or may not be enveloped
in lipid bilayer envelope
(mostly animal viruses)
◦ Requires host cell to
reproduce!
http://www.chm.bris.ac.uk/webpr
ojects2006/Kelly/influenzafigure1.
jpg
Is it alive?
?

Viruses do not quite fit the
all of the definitions of life
http://3.bp.blogspot.com/_jGXGQi_LBM/Sq5j9GjgkI/AAAAAAAAACI/aUOfmBDZdr0/s3
http://travelerfolio.com/tf2/photos/201 http://affordablehousinginstitute.org/bl
0/03/funny-frankenstein-monster.jpg
ogs/us/wpcontent/uploads/borat_thumbs_up.jpg
Definitions of
Life
Homeostasis
Organization
Metabolism
Growth
Adaptation
Response to Stimuli
Reproduction
Viral Structure

3 components
◦ 1. Nucleic Acids (DNA or RNA)
◦ 2. Capsid made from protein,
 May be helical or icosohedral (20 triangular sides)
◦ 3. Envelope
 Made from lipids when virus exits cell
 No envelope  naked
http://www.proprofs.com/flashcards/up
load/a3545428.jpg
Viral Genomes

DNA or RNA
◦ Both can be single
stranded (ss) or double
stranded (ds)
◦ DNA or RNA affects
where the protein
replicates in the cell
◦ May be segmented 
genes on separate
pieces on nucleic acid
http://www.mcb.uct.ac.za/tutorial/geno
mes.gif
Capsids



Capsomers encoded by 1 or 2 genes
Multiple protein protomers (capsomer) form
the capsid via self assembly
Protect genetic material
http://www.youtub
e.com/watch?v=X8MP7g8XOE&featur
e=related
http://www.nicerweb.com/bio1151
/Locked/media/ch19/19_03ViralStructure-L.jpg
Capsids and Symmetry



Primarily made of symmetric capsomers
forming hexamers
Requires a certain number of asymmetric
capsomers
Some use a triangular capsomer system
http://en.wikipedia.org/wiki/Icosahedral_capsid
Capsids and Symmetry

Symmetric capsomers make up helical
capsids forming a helix.
http://o.quizlet.com/i/aD6L0oSIeUjYrwx3qRka0w_m.jpg
The Envelope



Derived from cell membrane of host cell
Aids in entry into the host cell
Contains glycoproteins
http://education.expasy.org/image
s/Fusion_plasmamb.jpg
Well, what is a
glycoprotein?



Lock and Key mechanism  viral
glycoproteins interact with cell surface
receptors to gain entry into host cells
Called peplomers on the virus
http://www.youtube.com/watch?v=yEAf8gF9
wTU&feature=fvwrel
http://withfriendship.com/images/e/21947/Glycoproteinpicture.gif
Lock and key means
susceptibility

Cells must have a glycoprotein that
corresponds to the peplomer in order to be
susceptible. Ex. CD4 cells and HIV
http://www.elmhurst.edu/~chm/vchembook/images/571lockke
y.gif
Susceptibility vs.
Permissiveness




Susceptibility: ability to be infected
Permissive: ability for virus to replicate and
bud off virions in an infected cell.
Vectors  may be infected but not permissive
Nonpermissiveness due to antiviral response
Antiviral Response

Infected cell presents antigens

◦ primes humoral immune response
◦ Puts the cell and surrounding cells
into a static state
◦ Signals for NK cells to kill the
infected cell
http://images.tutorvista.com/content/immunesystem/interferons-action.jpeg
Resealing the envelope


Enveloped viruses get a new envelope by
budding from the host cell
Virus contains peplomers and glycoproteins
from the cell!!
http://www.lolpix.com/_pics/Funny_Pictures_340/Funny_Pictur
es_3403.jpg
http://www.prism.gatech.edu/~gh19/b1510/repc
Lytic vs. Lysogenic Cycle
http://diverge.hunter.cuny.edu/~weigang/Images/1312_lysogeniccycle_1.jpg
+ vs – Stranded Viruses
Steps of Viral Replication
(1) Attachment/Adsorption
(2) Penetration
-Receptor-Mediated Endocytosis
-Fusion Proteins
-Translocation
(3) Uncoating
(4) Transcription of Early mRNA
(5) Translation of Early Proteins
Replication (cont.)
(6) Replication of Viral Nucleic Acid
(7) Transcription of Late mRNA from
Progeny Genomic Nucleic Acid
(8) Translation of Late Proteins
(9) Assembly
(10) Release of Viral Progeny
-Host Cell Lysis
-Budding
* Link
Influenza: AKA the Flu

Key virulence
factors:
◦ Neuraminidaseenables virus to
be released from
host cell
◦ Hemagluttininbinds virus to cell
to enter and exit

H#N# signifies
variations of
these proteins
http://publications.nigms.nih.gov/findings/mar06/agbandjemckenna_files/images/image3.png
Herpes Simplex (HSV-1)
Herpes Simplex (HSV-2)
Varicella Zoster (VSV)
Ebstein-Barr (EBV)
Human Papilloma Virus
(HPV)
Coronavirus
Orthomyxovirus
Rhinovirus
Ebola
“In biology, nothing is clear,
everything is too complicated,
everything is a mess, and just when
you think you understand something,
you peel off a layer and find deeper
complications beneath. Nature is
anything but simple.”
“When people asked him why he
didn’t work with those viruses, he
replied, ‘I don’t particularly feel like
dying.’”
“It showed a kind of obscenity you
see only in nature, an obscenity so
extreme that it dissolves
imperceptibly into beauty.”
“Humans in space suits make
monkeys nervous.”
Human Immunodeficiency
Virus (HIV)
-RNA Retrovirus
-Transmission:
(1) Anal, Oral, Vaginal
Intercourse
(2) In Utero
Deaths attributed to HIV/AIDS: 1.8 Million (approx. 6.7 Billion worldwide)