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Viruses

Amanda Vang Evolution, Ecology, and Diversity Englisch 30 Karten

Structural classes: Icosahedral capsids

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  1. 1Size of viruses10^-7 to 10^-8
  2. 2Virus Characteristics1. Small, infectious
    2. Obligate intracellular parasites: depend on host cells to replicate
    3. Exist on borderline of definition of life
    4. No ribosomes
    5. Parasites of translation
  3. 3Virion1. Virus particle
    2. Consists of nucleic acid genome surrounded by coat proteins call capsids that may be enveloped in host-derived lipid bilayer
  4. 4Viral Genome1. Consist of either RNA or DNA
    2. May be single, double, or partially double-stranded
    3. May be circular, linear, or segmented
  5. 5Viruses: Unifying Principles1. All viruses package their genomes inside the capsid that mediates transmission of the viral genome from one host to next
    2. Viral genome contains information for initiating infectious cycle within susceptible, permissive cell
    3. Infectious, cycle includes attachment and entry of particle, decoding of genome information, translation of viral mRNA by host ribosome, genome replication, and assembly and release of particles containing the genome
  6. 6What viruses need to survive/replicate?1. Find and get into host: must get genome to replication site
    2. Make viral proteins: must make mRNA
    3. Make viral genome: used host cell's machinery in cooperation with viral particles
    4. Form progeny virions: genome and capsid must be transported thru cell to assembly site
    5. Spread within + between hosts: propagate into new cells for survival
    6. Overcome host defense
  7. 7Viral diseasesConsequences of the way each virus deals with trying to survive and replicate
  8. 8Challenges to Tracing Evolution of Viruses1. No proofreading activity in RNA polymerases (lots of mutations)
    2. High rate of replication
    3. Genomes are segmented
    4. Intense selective pressure (immune response)
    5. Viruses invade diverse species
    6. Unable to make phylogenetic tree
  9. 9Diversity and Evolution1. No genetic equivalent to ribosomal-RNA or universal proteins in bact, euk, or arch
    2. Virus-specific proteins only found in viral groups
    3. Protein phylogenies have only been useful to tentatively establish classification for selected virus groups
  10. 10Origin of Viruses: Progressive Hypothesis1. Come from mobile genetic elements (transposans)
    2. Fragments of DNA gained ability to leave their original cells and enter others
    3. Explains retroviruses
    4. Evolution of capsid proteins influenced infection of undamaged cells
  11. 11Origin: Regressive Hypothesis1. Viruses are remnants of more complex cellular organisms
    2. mimivirus: contains relatively large amount of putative genes associated with translation - may be remnants of previously completed translation system
  12. 12Origin: Virus-First Hypothesis1. Existed before cellular life
    Self-replicating units in ancient virosphere may have gained ability to form membranes and cell walls
    3. Led to evolution of three domains of life
    4. Viruses then continued to evolve with evolving hosts
  13. 13Discussion: Are viruses alive?What defines life?
    1. Homeostasis
    2. Energy metabolism
    3. Response to stimuli
    4. Reproduce
    5. Growth via cellular division (instead of replication via self-assembly)
    Viruses do nothing unless they enter a host cell
  14. 14How are viruses named?1. Disease they cause
    2. Type of disease they cause
    3. geographic location
    4. discoverers
    5. how they were thought to be contracted
    6. Combinations above
  15. 15Baltimore Classification System1. Based on genetic contents and replication strategies
    2. Seven categories
  16. 16dsDNA viruses1. Use host's DNA/RNA polymerase
    2. Viral proteins translated w/ host machinery
    3. Capsids form around newly replicated viral DNA molecules & released from cell
    4. Dependence on host cell replication limits target to growing cells
    5. some encode for own DNA polymerases to ensure replication in dormant cells
    6. Others produce protein that induces resting cell to active cell
    7. presence of virus and viral growth-promoting protein can cause unceasing growth and cell division
    Ex: HPV in cervix
  17. 17ssDNA viruses1. Genomes can't be used to make viral proteins - needs to make double stranded first
    2. Must convert ssDNA to dsDNA using host cell DNA polymerase
    3. (+)ssRNA is made by host cell RNA polymerase
    4. transcripts are translated to make viral proteins
    5. replicated viral DNA is coverted back into ssDNA genome
    6. virion packaged for export
    Ex: canine, feline parvo viruses
  18. 18dsRNA viruses1. genome has 10 distincts dsRNAs
    2. Virions carry an RNA polymerase that transcribes the dsRNA (+)ssRNA
    3. transcripts serve as mRNA that is translated into viral proteins or act as template for (-) strand synthesis; can be converted back into dsRNA genome for packaging
    4. Reoviruses (respiratory, enteric, orphan)
    Ex: rotavirus
  19. 19ss(+) RNA viruses1. genome functionality identical to mRNA molecules; host cell doesn't have mechanism to replicate RNA
    2. Direct access to host ribosomes; translation of virion RNA as mRNA
    3. Synthesis of (-)sense RNA on (+)sense template by RNA-dependent RNA Polymerase (no H bonds are formed between complementary strands)
    4. Synthesis of (+)sense RNA and mRNA using (-)sense RNA
    5. Translation of (+)sense and mRNA, synnthesis of structural protein
    6. Assembly of structural protein and (+)sense RNA and maturation of virions
  20. 20ss(-)RNA viruses (largest group)1. contains viral RNA-dependent RNA polymerase aong with (-)ssRNA genome w/in nucleocapsid
    2. once inside cell, viral polymerase begins to work on (-)ssRNA making 2 kinds of (+) stranded viral RNA
    3. some (+)stranded RNA is made as short viral mRNAs that are translated into viral proteins
    4. Some made as full length RNA that's replicated to make (-)ssNA genome that's needed for progeny virions
    5. Nucleocapsid assembly and maturation, budding of nucleocapsid thru host membrane containing viral envelope proteins
    6. Must be positive strand to make proteins
  21. 21RNA reverse transcribing viruses1. virion RNA is used as template to make DNA copy of viral genome
    2. Copying RNA to DNA is foreign for host cell and must be carried out by viral enzyme that's packaged in virion (reverse transcriptase)
    3. once viral dsDNA synthesized, transported into nucleus where it's inserted and covalently linked to host chromosomal DNA (integrase)
    4. integrated virus (provirus) can now be transcribed by host cell into (+)RNA that is transported to cytoplasm and used either as mRNA in viral potein synthesis or as genome for new progeny viruses
    5. No proofreading so lots of mutations
    Ex: HIV
  22. 22DNA reverse transcribing viruses1. Replication takes place in cytoplasm + nucleus of host cells
    2. viral DNA forms supercoiled mini-chromosomes structures upon entering host nucleus
    3. viral DNA transcribed to RNA that enters cytoplasm where it as two roles: template for viral protein synthesis or undergo reverse transcription by viral encoded reerse transcriptase to make dsDNA
    4. DNA can then reenter nucleus for amplification
    5. these viruses aren't considered true dsDNA viruses since use RNA intermediate
    6. do not require integration of viral genome into host's; their genome does not encode enzymatic protein integrase
  23. 23Virus ClassificationOrder: -virales
    Family: -viridae
    Subfamily: -virinae
    Genus: -virus
    Species
    Order based on inference that each virus family contains viruses that have mostly likely evolved from common ancestor
  24. 24Structural classes: Icosahedral capsidsStructural classes: Icosahedral capsids
  25. 25Structural Classes: Helical Symmetryidentical protein units called protomers self-assemble in helical arrayStructural Classes: Helical Symmetry
  26. 26Structural classes: non enveloped + envelopedStructural classes: non enveloped + enveloped
  27. 27Bacteriophage1. Bacteria is host
    2. Subcellular structure without metabolic machinery
    3. dsDNA, ssDNA, RNA
    4. Virulent phage vs. template phage
  28. 28Good viruses1. Viruses that have long association with host so relationship has become essential for survival of host
    2. Viruses attenuate diseases caused by other viruses or other pathogens
    3. Viruses that are useful to their hosts b/c they kill competitors
    4. Viruses that help their hosts adapt to extreme environmental
  29. 29Types of virus-host mutualismHerpesviruses: suppresses HIV in humans, protects against bacterial infection in mice
    Polydnavirus: wasps lay eggs in larva which have immune system to destroy eggs, but wasp genes carry virions that suppresses response
  30. 30Viruses as natural weapons1. Bacteria carry viral genome integrated into their own genome
    2. host immune to lytic forms of the virus
    3. Can attack other bacteria once excised from genome and reproduced

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Evolution, Ecology, and Diversity (Exam 2) Karteikarten am Viruses, erstellt von Amanda Vang am 02/11/2017.
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