Transcript Viruses
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/_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)