Lecture 73/73: Intro & Viral Replication Flashcards
what are the 4 structural forms that a virus can take?
1) Protein Icosohedron (the naked capsid) – nucleoprotein enclosed only by icosohedron – eg poliovirus
2) Protein Icosohedron enclosed by lipid protein envelope — eg herpesvirus
3) Helical Nucleocapsid coil enclosed by lipid protein envelope – eg Influenza virus
4) “Complex” – eg pox viruses
Properties of the naked virus
Environementally Stable
Released from cell via lysis
Can survive in the gut
Antibody may be sufficient immuno-protection
Properties of the Enveloped Virus
- components
- Properties
- consequences of properties
- Immunity
Components:
- membrane lipids from host cell
- embedded viral proteins and glycoproteins
Properies -
Labile; easily disrupted by acid, detergenct, drying and heating
Released by budding
Consequences;
Must stay wet; cannot survive the GI tract; spread in secretions, droplets
Immunity – need both antibody and cell mediated immune response
what are the 4 Viral Classification Schemes
ICTV – International committee on taxonomy of virus
Linnean System
Baltimore System
Disease Based
Describe the Baltimore scheme
based on how mRNA is made from genome –
dsDNA ssDNA -- dsRNA -- reoviruese Positive sense ssRNA negative sense ssRNA ssRNA RT viruses -- retrovirus dsDNA RT -- hepadnaviruses
Describe the Linnean System
suffixes
Order --- virales Family --- viridae Subfamily --- virnae Genus- -- virus Species --- eg measles virus
What are the steps of Viral Replication
Attachment and Recognition Penetration (fusion and entry) Uncoating Viral Protein Synthesis Viral Genome Replication Assembly (Budding) Release
Describe Attachment and Recognition
Passive kinetic process
Virus Attachemnt Protein binds to Cellular Receptor
Major determinant of tropism
Enveloped virsues – VAPs are envelop proteins (or spike proteins)
Non enveloped viruses – VAPs on the capsid,
Describe Penetration
- what are the three different patterns of entry
Energy Dependent Process; cell must be metabolically active for this to occur
Entry Patterns
Enveloped:
1) Fusion at the PM –
2) Fusion with Internalized Endosome –
Non Enveloped
1) Endocytosis – intracellular pH drop – entry into cytoplasm
Viral Protein Synthesis
- what proteins are made early? which are made late ?
§ Regulatory proteins – made early
□ Enzymes: polymerases, integrase, protease,
§ Structural Proteins – made late
□ Capsid, matrix, envelope
Viral Genome Replication
- where does this occur? what type of viruses ?
In the cytoplasm – most but not all RNA viruses
+poxvirus (DNA virus)
In the Nucleus – all DNA viruses except for Pox
some RNA viruses
Assembly
§ Occurs via Self Assembly
§ Begins with nucleocapsid assembly
□ If budding – this process will not be complete until budding occurs
□ If lysis (such as naked icosahedrals) – become fully assembled in the clel cytoplasm where they await their release
Release
General term for how fully formed virions escape the cell
Budding
Lysis – loss of cell membrane integrity
what is the reason for viral genomes high mutation rate?what are the consequences of a high mutation rate?
RNA-dependent RNA polymerases (unlike cellular DNA and RNA polymerases) tend to lack proofreading capability.
Mutation rate: 1 per 10,000 Nucleotides
Medical Consequences: viral serotypes for which cross-reactive immunity is minimal drug-resistant viral mutants evolve rapidly jump species.
What are the outcomse of the viral infection at the cellular level
Lytic: Use of cells resources to have high progeny May prevent the cell from dying Cell eventually exhauseted and dies -Abortive Virus enters the cell At any stage of Virus cycle interrupted; no new virions
- persistence Cell stays alive (likely from viral preventing it from committing suicide) Continues to make more virus Makes virus but at low rate Such as HepC - latent Genome present in the nuclues But no protein synthesis Something triggers a reactivation -- lytic - Transformed Cells immortalized Oncogenic viruses
