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28 Cards in this Set
- Front
- Back
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Virus
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-the minimum infectious unit
-a macromolecular complex consisting of protein, glycoprotein, and lipid -these ensure protection, transmission and replication |
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Steps of the viral life cycle
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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 |
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Prion
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-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 |
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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 |
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Describe an icosahedral nucleocapsid.
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-cubical
-histologically appears spherical with "bumpy" edges -20 faces -may or may not be enveloped |
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Describe a helical nucleocapsid.
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-histologically appear as long filaments
-ALL ARE ENVELOPED -ALWAYS CONTAIN RNA GENOMES -encapsidation of an RNA genome by capsomeres that form a coil |
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What is significant about a STRUCTURAL viral protein?
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it is one that is physically associated with the virion
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What is the function of a structural protein? (2)
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-protects the genome from chemical/enzymatic degredation
-regulates expression of the genome |
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What is the clinical relevance of a viral protein? (2)
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-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 |
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What types of nucleic acid genomes are present?
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-single stranded RNA (+ or - sense)
-double stranded RNA (++, --, or +-) -double stranded DNA + sense=identical to mRNA - sense=complimentary to mRNA |
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What are some characteristics of the nucleic acid genome?
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-haploid (*except Retroviruses*)
-encodes few proteins -much info encoded in a small amount of sequence -both strands of a ds DNA may be coding |
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What is the clinical relevance of the type of viral genome?
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-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 |
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What are some characteristics of the DNA viral genome?
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-tendency to establish latent or persistent infections
-may induce growth disturbances of infected cells |
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What are some characteristics of RNA viral genomes?
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-characterized by high plasticity (high degree of genetic drift)
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Describe structural proteins mediating viral gene expression and replication.
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-enzymes or enzyme cofactors
-transcriptases designed to read novel templates -transcriptases designed to read conventional templates in atypical locations |
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Give examples of transcriptases not normally utilized in the cell.
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-RNA-dependent RNA polymerase (for RNA viruses
-Reverse transcriptase (DNA from RNA) exs. hepadnaviruses retroviruses |
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Give examples of transcriptases designed to read conventional templates in unconventional locations.
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-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 |
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What is the importance of virus-encoded NON-STRUCTURAL proteins?
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-regulatory proteins
-they alter host cell metabolism -alter viral polymerase activities -process unique viral transcripts |
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What is the clinical significance of structural proteins mediating viral gene expression and replication?
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-detection of novel enzymatic activities may be used to detect viral infection
ex. detection of reverse transcriptase for retroviral infection |
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Describe STRUCTURAL proteins mediating attachment/penetration of target cells.
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-they are directly associated with the nucleocapsid
-they are inserted into a viral envelope, a lipid membrane of host-cell origin |
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What are two structural proteins associated with the viral envelope and what do they do?
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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 |
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What is the clinical relevance of structural proteins mediating attachment/penetration of the target cells?
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-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 |
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What is the clinical significance of a viral envelope?
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-it enhances the potential for a virus to change attachment proteins since they are no longer integrally linked to encapsidation function
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How are viruses classified?
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1. based upon structure
(type of nucleic acid) 2. groupings based upon routes of transmission |
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Describe the VIRAL FAMILY classification.
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-based upon type of nucleic acid
-ends with suffix -viridae |
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Describe the VIRAL GENERA classification.
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-based upon differences in genome organization
*important for replication strategy* -ends with the suffix -virus |
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Describe the VIRAL SPECEIS classification.
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-common names given to specific viruses withing a genus that cause a disease or spectrum of diseases
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Describe VIRAL TYPES, SUBTYPES, STRAINS AND VARIANTS.
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-distinct viral phenotypes or biotypes
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