MICB Lecture 4

Cards (46)

  • Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the strain that causes the disease covid 19.
  • What are viruses
    obligate, intracellular parasites
  • Features of viruses
    protein + nucleic acid, small (nm)
  • What virus and how many genes
    Parvovirus - 3 genes
  • What virus and how many genes
    Mimivirus - 900 genes
  • virion
    complete virus particle
  • capsid
    protein coat around genome
  • nucleocapsid
    nucleic acid + capsid and either DNA or RNA
  • protomer
    protein subunit of capsid
  • Simplest virions consist of only a nucleocapsid
  • envelope virus: virions covered by a lipid membrane, those lacking a membrane are called naked viruses
  • viruses lack ribosomes for protein synthesis, a mechanism for generating ATP and a cytoplasm
  • naked virus: construct capsid from many copies of one protein and a few minor proteins
  • enveloped virus: require both nucleocapsid proteins and additional proteins to anchor the membrane
  • spikes: on enveloped virus, made from the virus, involved in attachment to host cell surface
  • Morphological type
    Helical: hollow tubes with protein walls, ex: tobacco mosaic virus
  • Influenza virus
    RNA is segmented and capsids are helical
  • Morphological type
    Icosahedral: efficient way to enclose space
    • 20 triangular faces w/ ring shaped units of 5 or 6 protomers
  • What symmetry and associated features
    Binal
    • icosahedral head (genetic info injected there, genome inside) and helical sheath
    • bacteriophages infect bacterial (and archaeal) cells
    • often results in cell lysis
    • CRISPR/Cas: bacterial defense mechanism to prevent phage attack
    A) T-4 bacteriophage
  • What symmetry
    Complex:
    poxviruses
    • virions among the largest of the animal viruses
    • ovoid, brick shape
  • Viral envelopes
    the capsid of some viruses is enclosed in an envelope (comes from host cell membrane)
    A) Envelope
    B) tegument
    C) capsid
  • Name virus and proteins within it
    Hemagglutinin spike: binds host sialic acid
    Neuraminidase spike: cleaves host lipids/proteins to release virus
    envelope: lipid bilayer
    RNA replicase: use RNA template to make RNA
    Influenze subtype H5N2: H=hemagglutinin and N=neuraminidase
    A) influenza virus
    B) hemagglutinin spike
    C) Envelope
    D) rna replicase
    E) segmented RNA genome
    F) H5N2- subtype
    G) neuraminidase spike
  • Genome
    all genetic material in an organism
  • Viral genomes can be
    DNA or RNA
    ss or ds
    linear or circular
    genome encodes the viral proteins
  • How to classify viruses
    over 2000 viruses have been described and placed with these key defining properties
    1. nucleic acid type
    2. capsid symmetry
    3. presence/absence of envelope
  • Five features of Coronavirus
    Nucleic acid: RNA
    Symmetry/capsid: helical
    naked or enveloped: enveloped
    Genome architecture: +ss
    Baltimore class: IV
  • How to cultivate bacteriophages
    bacteria and archaea cells
  • how to cultivate animal viruses
    suitable animals, embryonated eggs
    animal viruses are grown in cell culture on monolayers of animal cells
  • plaques
    results from lysis by virus, localized area of cellular destruction
  • how to cultivate tissue (cell) cultures
    cell monolayers
    • plaques
    • plaque assays (virion numbers expressed as plaque forming units)
  • Viral multiplication/infectious cycle
    attach to cell host - proteins initiate
    2. entry and uncoating
    3. synthesis of viral proteins and nucleic acids
    4. assembly of capsids
    5. release of virions
  • Animal virus attachment
    viral surface proteins mediate attachment to host receptors - carbohydrates, proteins and lipids
    ex: influenza hemagglutinin, HIV gp (glycoprotein)120, SARS-CoV-2 ACE2 receptor
  • ACE2 receptor
    cleaves hormone angiotensin, regulates blood pressure
  • Animal virus entry
    virus genome or entire nucleocapsid enter cytoplasm, once inside some shed their capsid proteins (uncoating)
  • Two types of entry
    Fusion: involves viral envelope glycoproteins or phospholipids that interact with proteins in the plasma membrane of host cell
    Endocytosis: enter ells by one of the endocytic pathways (including clathrin-dependent endocytosis and macropinocytosis), resulting endocytic vesicle contains virion and fuses with endosome
    A) Fusion
    B) endocytosis
  • once viral infection of a host cell has occurred
    viral genome is replicated
    viral mRNA made (via transcription) used to make viral proteins (for translation)
  • Central Dogma of information flow
    Replication: utilize DNA polymerase
    Transcription: DNA template to make RNA
    Translation: RNA template to make sequence of amino acids, then folded into protein
    DNA -> RNA -> protein
    A) replication
    B) transcription
    C) translation
  • RNA viruses typically replicate in
    cytoplasm, use viral RNA replicase to make RNA
  • Four types of RNA viruses
    dsRNA
    +ssRNA
    -ssRNA
    retroviruses
  • +ssRNA
    genomes act directly as mRNA
    upon entry and uncoating, host ribosomes translate viral +RNA into protein
    ex: polio, zika