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Virus (Virion Particle)

Virus (Virion Particle). The Capsid is the protein shell surrounding the virus nucleic-acid genome A Nucleocapsid is that combination of protein capsid and nucleic-acid genome Capsids consist of multiple subunits of one or more types of protein Capsomere(s) = capsid protein subunits

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Virus (Virion Particle)

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  1. Virus (Virion Particle)

  2. The Capsid is the protein shell surrounding the virus nucleic-acid genome • A Nucleocapsid is that combination of protein capsid and nucleic-acid genome • Capsids consist of multiple subunits of one or more types of protein • Capsomere(s) = capsid protein subunits • For viruses with complex morphologies the capsid may consist of many (10s of) different types of capsomer proteins, with additional proteins involved simply in capsid morphogenesis • Capsids are responsible for nucleic-acid protection and penetration into cells Capsid (Nucleocapsid)

  3. In addition to the capsid, many animal viruses additionally posses Envelopes • An Envelope is a lipid bilayer that surrounds the nucleocapsid • For enveloped viruses the envelope is also (in addition to the capsid) involved in nucleic-acid protection and penetration • Without an envelope an otherwise enveloped virus is not mature nor infectious • Enveloped proteins often have Glycoproteins (Spikes) projecting from their envelopes that are involved in virus infection • For Non-Enveloped viruses the capsid is solely responsible for nucleic-acid protection and penetration Virus Envelopes (Spikes)

  4. Viruses are classified: • According to their Genome Type • Their Virion Morphology (as determined by electron microscopy) • Their strategies of replication • Their Serology (serotype), which is their reaction with specific antiserum • (Increasingly) in terms of the sequence of their genomes • International Committee on Taxonomy of Viruses (ICTV) Virus Classification

  5. Single Stranded DNA Double Stranded Double Stranded Negative RNA Single Stranded Positive ssRNA  dsDNA  ssRNA (the retroviruses) http://www.virology.net/Big_Virology/BVFamilyGenome.html Viral Genomes One way to distinguish different types of viruses (e.g., influenza virus from HIV) is in terms of the characteristics of their nucleic-acid genomes Nucleic-Acid Virus Genome

  6. Adsorption (attachment) • Penetration (nucleic-acid release) • Synthesis (of RNA and proteins, as well as DNA if DNA genome) • Maturation (assembly of virion) • Release (lysis or chronic release, e.g., budding, with the latter coinciding with release for various enveloped viruses) Steps of Virus Replication Caveat: It is important to realize that variation among viruses is between virus strains/species; any one kind of virus cannot replicate in multiple ways, have more than one virion morphology, or vary in genome type, etc.

  7. Lytic Phage Infection Cycle

  8. Temperate Phage Infection Cycle

  9. Naked Animal Virus Infection Lysis!

  10. Enveloped Virus Infection Budding, Not Lysis!

  11. HIV Infection Cycle Budding, Not Lysis!

  12. Viral products produced, host genome fragmented ~1 phage/10,000 will pick up chromosomal DNA... Transduction

  13. heteroduplex Competent cell: capable of picking up DNA Transformation Transformation: DNA picked up directly from the medium and recombined into the genome

  14. Plasmids

  15. Conjugation

  16. Resistance Plasmids

  17. Bacterial Genotype  Phenotype • Bacterial response to environmental change • Control of gene expression • Lac operon (response to presence of lactose) • Trp operon (response to presence of tryptophan) • Catabolite Repressor Protein (response to presence of glucose)

  18. Lac Operon without Lactose Enzymes required for Lactose Digestion are synthesized (to any great extent) only when Lactose is present in the environment

  19. Lac Operon with Lactose

  20. Negative Control Protein-DNA binding Inhibits Transcription Also Inducible Operon since lactose binding  transcription

  21. Trp Operon without Trp

  22. Trp Operon with Trp

  23. Feedback Inhibition

  24. Negative Control Protein-DNA binding Inhibits Transcription Also Corepressed Operon since Trp binding  transcription

  25. Positive Control Protein-DNA binding Enhances Transcription

  26. cAMP Receptor Protein

  27. Link to Next Presentation

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