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Viruses
http://www.bing.com/images/search?q=virus&view=detail&id=5AD62840C81847683B7591AEC1F651E75C9E986E&first=1
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!
What is a virus?
http://www.chm.bris.ac.uk/webprojects2006/Kelly/influenzafigure1.jpg
Is it alive?
http://3.bp.blogspot.com/_j-GXGQi_LBM/Sq5j9-GjgkI/AAAAAAAAACI/aUOfmBDZdr0/s320/RIP+Tomb+Stone.jpg
?
http://affordablehousinginstitute.org/blogs/us/wp-content/uploads/borat_thumbs_up.jpg
http://travelerfolio.com/tf2/photos/2010/03/funny-frankenstein-monster.jpg
Viruses do not quite fit the all of the definitions of life
HomeostasisOrganizationMetabolismGrowthAdaptationResponse to StimuliReproduction
Definitions of Life
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
Viral Structure
http://www.proprofs.com/flashcards/upload/a3545428.jpg
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
Viral Genomes
http://www.mcb.uct.ac.za/tutorial/genomes.gif
Capsomers encoded by 1 or 2 genes Multiple protein protomers (capsomer) form
the capsid via self assembly Protect genetic material
Capsids
http://www.nicerweb.com/bio1151/Locked/media/ch19/19_03-ViralStructure-L.jpg
http://www.youtube.com/watch?v=X-8MP7g8XOE&feature=related
Primarily made of symmetric capsomers forming hexamers
Requires a certain number of asymmetric capsomers
Some use a triangular capsomer system
Capsids and Symmetry
http://en.wikipedia.org/wiki/Icosahedral_capsid
Symmetric capsomers make up helical capsids forming a helix.
Capsids and Symmetry
http://o.quizlet.com/i/aD6L0oSIeUjYrwx3qRka0w_m.jpg
Derived from cell membrane of host cell Aids in entry into the host cell Contains glycoproteins
The Envelope
http://education.expasy.org/images/Fusion_plasmamb.jpg
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
Well, what is a glycoprotein?
http://withfriendship.com/images/e/21947/Glycoprotein-picture.gif
Cells must have a glycoprotein that corresponds to the peplomer in order to be susceptible. Ex. CD4 cells and HIV
Lock and key means susceptibility
http://www.elmhurst.edu/~chm/vchembook/images/571lockkey.gif
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
Susceptibility vs. Permissiveness
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
Antiviral Response
http://images.tutorvista.com/content/immune-system/interferons-action.jpeg
Enveloped viruses get a new envelope by budding from the host cell
Virus contains peplomers and glycoproteins from the cell!!
Resealing the envelope
http://www.prism.gatech.edu/~gh19/b1510/repcycvi.gifhttp://www.lolpix.com/_pics/Funny_Pictures_340/Funny_Pictures_3403.jpg
(1)Attachment/Adsorption
(2) Penetration -Receptor-Mediated
Endocytosis-Fusion Proteins-Translocation
(3) Uncoating
(4) Transcription of Early mRNA
(5) Translation of Early Proteins
Steps of Viral Replication
(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
Replication (cont.)
Key virulence factors:◦ Neuraminidase-
enables virus to be released from host cell
◦ Hemagluttinin- binds virus to cell to enter and exit
H#N# signifies variations of these proteins
http://publications.nigms.nih.gov/findings/mar06/agbandje-mckenna_files/images/image3.png
Influenza: AKA the Flu
“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.”
-RNA Retrovirus -Transmission:
(1) Anal, Oral, Vaginal Intercourse
(2) In Utero
Human Immunodeficiency Virus (HIV)
Deaths attributed to HIV/AIDS: 1.8 Million (approx. 6.7 Billion worldwide)