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Micro Exam 2: Viral Structure and Pathogenesis
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23
Microbiology
Undergraduate 2
10/29/2012

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Term
What is a virus?
Definition
A package of genetic information protected by a protein shell for delivery into a host cell to be expressed and replicated.
Term
What differentiates Viruses from other micro-organisms?
Definition
Nucleic acid - have only DNA or RNA, not both.
Lack a nuclear or external cell wall
Small genomes - produce only a limited number of proteins and have no intracellular systems.
Can only reproduce inside other cells (steal energy and mechanics of the host).
Term
Historically significant viruses
Definition
Polio
Small pox and Measles
Spanish Flu - after WWII killed many many many.
Nowadays - west nile, SARS, avian flue, pandemic influenza viruses.
Term
Viral taxonomy is based on?
Definition
Type and form of nucleic acid
Structure
Organization of genome
Antigenic differences.
Term
Genomic Organizations of viral nucleic acid
Definition
RNA - single, double.
DNA - single double.
Term
Single Stranded RNA - positive vs negative.
Definition
Pos - same direction as mRNA - can go directly to the ribosome and synthesize viral proteins.
Neg - must make a positive copy inside the cell to be translated.
Term
Double stranded RNA - two types.
Definition
Single piece or segmented(each segment codes for a different viral protein - mixing results in swine and avian flu).
Term
Double stranded DNA
Definition
Integrated into the genome.
Ex. Herpes virus.
Term
Capsomere
Definition
Structural subunits containing several proteins, aggregate together to form the viral capsid.
Term
Capsid
Definition
Associates with viral DNA to produce a nucleocapsid.
Term
Arrangements of nucleocapsid
Definition
Cubic - icosahedral(herpes) - 20 sides.
Helical - influenza virus.
Complex
Term
Viral Envelope
Definition
lipid structure, derived from cellular membranes(stolen from host).
Studded with surface projections.
Glycosylated by host systems to make them "sticky".
Term
Papilloma Virus
Definition
Naked Icosahedral DNA virus.
Term
Herpes Virus
Definition
Envelopped Icosahedral DNA virus
Term
Hepatitis
Definition
Enveloped icosahedral DNA virus
Term
Influenza
Definition
Enveloped Helical RNA virus
Term
Picornavirus
Definition
Naked, Icosahedral, RNA virus.
Term
Vertical transmission
Definition
From mother to fetus in utero.
Term
Phases of viral life cycle:
Definition
1. Attachment and internalization
2. Uncoating (cell uncoats it, hoping to destroy it).
3. Replication - Naked nucleic acid will synthesize protein(to become the next virus).
4. Assembly - DNA surrounds itself with capsomere proteins etc..Steals nuclear envelop and glycoproteins.
5. Egression - leave the cell.
Term
Consequences of Virus-Cell Interaction
Definition
Viral proliferation and cell lysis - host cell dies. Ex. Cold sores, Genital Herpes, Chicken pox.
Latent Infection - non-replicating virus. Can become integrated. Ex. HPV, Herpes.
Persistent Infection - ongoing viral replication, few or no symptoms. Ex. Hep C and B, HIV. Tissue injury may be induced by the virus or the immune response to the viral infection.
Oncogenesis - Cellular proliferation. HPV and cervical cancer. Hep B and C can cause liver cancer. EB - lymphoma.
No apparent Disease - Hep G.
Term
Dx of Viral infections
Definition
Clinical features typical to infection.
Lab Dx - histology and cytology, looking for viral antigens in tissue and serum, Antibody testing( IgG, IgM, very high IgG titer), virus isolation, DNA or RNA amplification.
Term
Prions
Definition
Proteinaceous infections particles.
An infectious agent composed of a protein. Does not self replicate, induces existing proteins to take on the rogue form. Highly resistant to heating and irradiation.
Term
Examples of Spongifrom encephalopathies
Definition
Human - Creuztfeldt-Jacob disease.
Animal - BSE(mad cow).
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