Viruses http://www.bing.com/images/sear ch?q=virus&view=detail&id=5AD6
2840C81847683B7591AEC1F651E
75C9E986E&first=1

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/_j-
GXGQi_LBM/Sq5j9-
GjgkI/AAAAAAAAACI/aUOfmBDZdr0/s3
20/RIP+Tomb+Stone.jpg
http://travelerfolio.com/tf2/photos/201
0/03/funny-frankenstein-monster.jpg
http://affordablehousinginstitute.org/bl 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=X-
8MP7g8XOE&featur e=related http://www.nicerweb.com/bio1151
/Locked/media/ch19/19_03-
ViralStructure-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/repcycvi.gif

Lytic vs. Lysogenic Cycle http://diverge.hunter.cuny.edu/~weigang/Images/13-
12_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)