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Unformatted text preview: Lecture 6: Virus Structure P2: Function of viral particles include: protecting the genome, having genetic economy so capsid made from one protein, and being able to deliver from cell to cell Methods to Study Virus Structure Pages 6-7, Book 86-89-Transmission electron microscopy: thin section needed, really bad for details-Cyro-EM: freezing of virus particles allows 3D structure, avoids water crystal formation; pretty good resolution- X-Ray Crys: the best resolution since u can actually see the molecular interactions between particles, but need high concentration of highly purified particle Enveloped Viruses (Page 4, book 114)-has a lipid bilayer that is acquired through budding from host membranes- envelope has multiple viral glycoproteins, which were localized to the cell membrane first before budding- nucleocapsid: nucleic acid, protein shell, envelope 1) VSV (Page 5)- G protein is synthesized an enters secretory pathway where it goes to plasma membrane- Virus proteins will interact with cytoplasmic side of G protein to help, these internal domains essential for virus assembly 2) Influenza Naked Viruses (Page 5)- protein capsid assembled in cytoplasm or nucleus- capsid: protein shell and nucleic acid 1) Poliovirus: naked icosahedron- has VP1, VP2 and VP3, to make a capsid- assembly coupled with genome replication (a +RNA virus) 2) Adenovirus: naked icosahedron , has fibers with knobs for attachment Capsid Structures (Pages 8- Subunit= single polypeptide Protomer/Asymmetric unit: a building block of capsid, 1+ subunits Two main structures: 1) Helical (Pages 9-10)- helical animal viruses are always enveloped- helix formed from single subunit and can be as long as possible- EXAMPLE: TMV- page 10: disc to dishwasher conformation as the RNA is threaded through 2) Icosahedral (Pages 10-13)- has 20 equilateral triangles with various axis of symmetry- each triangle has 3 subunits, so need 20*3= 120 subunits to make basic capsule- Triangulation Number : Page 12 T = (# subunits) / 60 T = (# protomers) / 3- for larger capsids, becomes difficult and quasi-equivalence happens Page 14-15: Interactions b/t protein subunits: are all NONCOVALENT (h-bonding, salt bridges, hydrophobic and van der waals interactions) 3) T4: syringe mechanism, assembly is very complicated 4) Reovirus and Rotavirus: a couple of protein shells Lecture 7: Virus Binding and Entry Things in the host cell surface: Pages 3 and 4 1) Attachment Factors : they are not required, make initial contact, are non-specific and concentrated, binding is reversible and does not change conformation, 2) Receptors and co-receptors...
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- Fall '07