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28 Cards in this Set

  • Front
  • Back
-the minimum infectious unit
-a macromolecular complex consisting of protein, glycoprotein, and lipid
-these ensure protection, transmission and replication
Steps of the viral life cycle
1. extracellular (transmission phase)
2. attachment and penetration of target cell
3. production of viral proteins
4. replication of the viral genome
5. assembly and release of infectious viral progeny
-an infectious protein
-malfolded variant of cellular membrane protein
-found in high concentrations in lymph and neural tissue
-"scrapie" prion misfolds the normal prion gene
-protease resistant
Describe a nucleocapsid.

What is this analagous to in the eukaryotic cell?

What two symmetrical forms can the nucleocapsid take on?
-consists of nucleic acids and structural proteins known as capsomeres
-it is analogous to the chromatin of eukaryotic cells
-the nucleocapsid can be icosahedral or helical
Describe an icosahedral nucleocapsid.
-histologically appears spherical with "bumpy" edges
-20 faces
-may or may not be enveloped
Describe a helical nucleocapsid.
-histologically appear as long filaments
-encapsidation of an RNA genome by capsomeres that form a coil
What is significant about a STRUCTURAL viral protein?
it is one that is physically associated with the virion
What is the function of a structural protein? (2)
-protects the genome from chemical/enzymatic degredation
-regulates expression of the genome
What is the clinical relevance of a viral protein? (2)
-detection of these proteins or a host immune response to these proteins may be used in the diagnosis of virus infection. (Must be produced in large quantity)
-morphology can be recognized by EM
What types of nucleic acid genomes are present?
-single stranded RNA (+ or - sense)
-double stranded RNA (++, --, or +-)
-double stranded DNA

+ sense=identical to mRNA
- sense=complimentary to mRNA
What are some characteristics of the nucleic acid genome?
-haploid (*except Retroviruses*)
-encodes few proteins
-much info encoded in a small amount of sequence
-both strands of a ds DNA may be coding
What is the clinical relevance of the type of viral genome?
-can diagnose specific viral infections by dectection of unique nucleic acid sequences by PCR
-predict viral replication strategy which in turn defines viral behavior in a host
-determines susceptibility to specific anti-viral agents
What are some characteristics of the DNA viral genome?
-tendency to establish latent or persistent infections
-may induce growth disturbances of infected cells
What are some characteristics of RNA viral genomes?
-characterized by high plasticity (high degree of genetic drift)
Describe structural proteins mediating viral gene expression and replication.
-enzymes or enzyme cofactors
-transcriptases designed to read novel templates
-transcriptases designed to read conventional templates in atypical locations
Give examples of transcriptases not normally utilized in the cell.
-RNA-dependent RNA polymerase (for RNA viruses
-Reverse transcriptase (DNA from RNA)
exs. hepadnaviruses
Give examples of transcriptases designed to read conventional templates in unconventional locations.
-cytoplasmic DNA dependent DNA/RNA polymerases
-used to read DNA in the cytoplasm
exs. poxviruses replicate in the cytoplasm, although they utilize a DNA genome
What is the importance of virus-encoded NON-STRUCTURAL proteins?
-regulatory proteins
-they alter host cell metabolism
-alter viral polymerase activities
-process unique viral transcripts
What is the clinical significance of structural proteins mediating viral gene expression and replication?
-detection of novel enzymatic activities may be used to detect viral infection
ex. detection of reverse transcriptase for retroviral infection
Describe STRUCTURAL proteins mediating attachment/penetration of target cells.
-they are directly associated with the nucleocapsid
-they are inserted into a viral envelope, a lipid membrane of host-cell origin
What are two structural proteins associated with the viral envelope and what do they do?
1. glycoprotein peplomers=virus-encoded products inserted into the envelop that mediate attachment/penetration
2. matrix protein=line the inner aspect of the envelope, conveying rigidity to it
What is the clinical relevance of structural proteins mediating attachment/penetration of the target cells?
-enveloped viruses are unstable outside of the host
-more difficult to maintain infectivity of enveloped viruses for diagnostic virus isolation
-enveloped viruses can be readily disinfected with detergents
What is the clinical significance of a viral envelope?
-it enhances the potential for a virus to change attachment proteins since they are no longer integrally linked to encapsidation function
How are viruses classified?
1. based upon structure
(type of nucleic acid)
2. groupings based upon routes of transmission
Describe the VIRAL FAMILY classification.
-based upon type of nucleic acid
-ends with suffix -viridae
Describe the VIRAL GENERA classification.
-based upon differences in genome organization
*important for replication strategy*
-ends with the suffix -virus
Describe the VIRAL SPECEIS classification.
-common names given to specific viruses withing a genus that cause a disease or spectrum of diseases
-distinct viral phenotypes or biotypes