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Summary of the last lecture. Virus classification schemes: Classical Recent: ICVT Baltimore Virus Structure: Virion DNA or RNA, virus replication enzymes Capsid, or nucleocapsid Icosahedral and helical Envelope(lipids and carbohydrates from cells) Glycoproteins (Gp, G): spikes

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summary of the last lecture
Summary of the last lecture
  • Virus classification schemes:
    • Classical
    • Recent: ICVT
    • Baltimore
  • Virus Structure: Virion
    • DNA or RNA, virus replication enzymes
    • Capsid, or nucleocapsid
      • Icosahedral and helical
    • Envelope(lipids and carbohydrates from cells)
    • Glycoproteins (Gp, G): spikes
    • Matrix protein
    • Assessory proteins
  • Virus assembly
    • Spontaneous
    • Protein-protein, protein nucleic acid and protein-lipid interaction (hydrophobic and electrostatic)
slide3

Mechanism of packaging genome

  • Direct contact of genome with nucleocapsid or capsid

proteins: small viruses such as poliovirus contain

specific proteins that interact with RNA.

  • Specialized viral encoded nucleic acid binding proteins:

these proteins, called ribonucleoproteins, nucleoproteins

or core proteins, contain a nucleic acid binding motif in

the sequence, or recognize a specific packaging signal

sequence in RNA or DNA. These proteins are highly basic

which react with negatively charged nucleic acids.

  • Packaging by cellular proteins: unique to papovaviruses, so

the small viral genome doesn’t need to devote its limited

genome to packaging.

cell culture
Cell culture
  • Medium for cell growth
    • -- water, salts, minerals
    • -- amino acids
    • -- glucose
    • -- serum
    • -- antibiotics (penicillin and streptomycin)
    • -- special growth factors (for some cell types)
  • Cell culture
    • -- primary cell culture: prepared freshly from tissue
    • -- cell lines (immortalized cell culture):directly derived from tumor or primary cells transformed with tumor virus or chemical mutagen
cell culture cont
Cell culture (cont’)
  • CO2 incubator: temperature 37oC, humidified, co2
  • Long term storage: at liquid nitrogen (-140oC). Cells should be frozen quickly in -80oC freezer and thaw rapidly at 37oC waterbath
cell types
Cell types

Fibroblast-like cells (BHK)

Epithelial-like cells

(Lung carcinoma)

cytopathic effects cpe
Cytopathic effects (CPE)

uninfected

0.01PFU of virus/cell infected

0.1PFU of virus/cell infected

10 PFU of virus/cell infected

cpe cont
CPE(cont’)

Intranuclear inclusion body(LM)

Syncytium

Intranuclear inclusion body(EM)

virus cell interaction
Virus-cell interaction
  • Attachment (reversible)

-- virus attachment proteins (capsids, or glycoproteins)

-- receptors or co-receptors (cell surface molecules)

-- virus tropism ( spectrum of cells that virus can infect)

  • 2. Entry (penetration cross the plasma membrane, irreversible)
    • -- Receptor mediated endocytosis (the most common)
    • -- Cell membrane fusion (usually enveloped virus)
    • -- Translocation: very rare
  • 3. Uncoating( release of nucleic acid from its protein coat)
    • -- uncoating at the plasma membrane (Paramyxovirus)
    • -- uncoating triggered by change in pH (Influenza)
    • -- uncoating in the cytoplama
virus cell interaction cont
Virus-cell interaction (cont’)
  • 4. Replication and protein synthesis
    • -- In general, early proteins ( viral enzymes, regulatory
    • proteins) are synthesized first, followed by virus
    • genome replication and late proteins (structural
    • proteins) synthesis
  • 5. Assembly and release
    • -- Non-enveloped virus become mature inside the cell
    • and are released by cell lysis
    • -- enveloped viruses mature by budding from the plasma
    • membrane of host cells
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