Chapter 6

Chapter 6 - Chapter 6- Virus Structure and Function General...

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Unformatted text preview: Chapter 6- Virus Structure and Function General Properties of Viruses (virions) • Obligate intracellular parasite made of nucleic acid surrounded by a protein coat. (basic structure, some have extra stuff) • Only replicate inside host • No nucleus, organelles, cytoplasm • Viral genomes contain • information for taking over host cell • information for making viral proteins • Capsid, genome replication proteins Virus Structure—Capsids • Capsid- protein coat surrounding the nucleic acid • Capsid proteins are arranged to give virion symmetry Icosahedral capsids • Roughly spherical • 20 equilateral triangles or faces that come together to make a rough round shape • Many animal viruses look like this Filamentous capsids • Long tube of protein , with genome inside (instead of icosahedral capsid) • Tube made up of 100’s of identical protein subunits • Tube length reflects size of viral genome Complex capsids • Mixture of icosahedral & filamentous shapes • Many bacteriaphage (viruses that infect bacteria) Asymmetrical (irregular) shapes • Tend to be larger viruses • Poxviruses (like smallpox) Virus Structure—Envelopes • Envelope- lipid bilayer around capsid of some viruses • Allows fusion to host cell or organelle membrane (in order to infect cell. Fuses to either cytoplasmic membrane or organelle membrane) • Only occurs if host cell not covered by cell wall • Bacteriophages are NON-enveloped because they infect something with a cell wall. Plant viruses wouldn’t have one either) • Envelope lipids come from host (they take it from the host as they leave) • Not encoded by a viral genome • But, proteins embedded in envelope may be encoded by virus • Coats viral capsid as virus leaves cell or organelle (with cm as it leaves the cell) Virus Structure—Genome • DNA or RNA • Single-stranded (ss) or double-stranded (ds) (remember ours is double stranded) • Linear or circular • Includes genes encoding viral proteins • capsid • envelope proteins if virus is enveloped • Any polymerase not found in host cell Bacteriophage Life Cycles (a lot of these things are specific to bacteriophage and do not apply to animal viruses) 1. Attachment to host cell receptor proteins • Bacterial cell receptors normally used for bacterial purposes (not something that’s there for the virus to attach to)...
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This note was uploaded on 05/07/2011 for the course BIOL 2153 taught by Professor Larkin during the Spring '03 term at LSU.

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Chapter 6 - Chapter 6- Virus Structure and Function General...

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