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

Lytic vs. Lysogenic Cycle

http://diverge.hunter.cuny.edu/~weigang/Images/13-12_lysogeniccycle_1.jpg

+ vs – Stranded Viruses

(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.)

* Link

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

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.”

-RNA Retrovirus -Transmission:

(1) Anal, Oral, Vaginal Intercourse

(2) In Utero

Human Immunodeficiency Virus (HIV)

http://www.wellcome.ac.uk/Education-resources/Teaching-and-education/Animations/Viral-diseases/index.htm

Deaths attributed to HIV/AIDS: 1.8 Million (approx. 6.7 Billion worldwide)

Thanks!