Exam #1: Medical Virology Flashcards by Jonathan Kallevang

Describe the general characteristics of viruses.

Acellular
Obligate parasite i.e. do NOT carry out own metabolism & lack organelles/ ribosomes
20-300 nm in size–same size are smallest bacteria

How well did you know this?

Not at all

Perfectly

What are the different types of virions? Which is generally more vulnerable to the environment?

Capsid (protein coat as exterior)

- Enveloped (lipid coat exterior, outside of capsid) & more vulnerable

How well did you know this?

Not at all

Perfectly

What is the matrix or tegument of a virus?

Space between the capsid & envelope

How well did you know this?

Not at all

Perfectly

What are the different types of genomes that viruses may contain?

Segmented or continuous
DNA or RNA
Double stranded (ds) or Single stranded (ss)
Positive or negative sense

How well did you know this?

Not at all

Perfectly

What is the difference between positive & negative sense?

Positive= in correction orientation for translation i.e. like an mRNA molecule
Negative= opposite orientation needed to be a direct template for translation i.e complementary to mRNA

How well did you know this?

Not at all

Perfectly

How are viruses classified?

Genome (which tells how the virus replicates)

- Class of disease caused

How well did you know this?

Not at all

Perfectly

What family of viruses contains ssDNA?

Paroviridae

How well did you know this?

Not at all

Perfectly

What families of viruses contains dsDNA?

Papovaviridae
Adenoviridae
Herpesviridae
Poxviridae 		
Hepadnaviridae

How well did you know this?

Not at all

Perfectly

What is the family of dsRNA viruses?

Revoviridae

How well did you know this?

Not at all

Perfectly

What are the families of -ssRNA viruses?

Orthomyxoviridae 
 Paramyxoviridea 
 Rhabdoviridae 
 Bunyaviridae 
 Arenaviridae 
 Filvoiridae

How well did you know this?

Not at all

Perfectly

What are the families of +ssRNA viruses?

Togaviridae
Flavaviridae
Coronaviridae
Retroviridae
Picornaviridae
Caliviridae
Hepeviridae

How well did you know this?

Not at all

Perfectly

What are the properties of RNA viruses?

RNA is more labile (liable to change/easily altered) & transient than DNA
Replicate quickly
Cells cannot replicate RNA; thus, RNA viruses must encode an RNA-dependent-RNA polymerase
Prone to mutation b/c polymerase does NOT have proofreading mechanisms

Clinical impact= RNA viruses are more adaptable to environment & more easily evade the immune system

How well did you know this?

Not at all

Perfectly

What are the three major forms of capsids?

Helical- slinky
Icosahedral- 20 sided dye
Complex- less ordered than icosahedral & in large viruses

How well did you know this?

Not at all

Perfectly

What is a Naked Capisd?

Virus does not have an envelope & uses the capsid as its outermost shell
Spread by lysis–> must kill cell to spread

How well did you know this?

Not at all

Perfectly

What are the clinical implications of having a naked capsid?

Environmentally stable
Spread easily
Dry out & retain infectivity
Survive in adverse conditions
Resistant to detergents & poor sewage treatment

How well did you know this?

Not at all

Perfectly

What is an enveloped virus & what are the characteristics of enveloped viruses?

Enveloped virus= has lipid layer outside of capsid

Environmentally labile
Modify cell membrane during replication
Released by lysis or budding (not killing cell for release)

How well did you know this?

Not at all

Perfectly

What are the clinical implications of enveloped viruses?

Must remain wet
Cannot survive in GI tract
Spread in large droplets
Do NOT need to kill cell to spread

How well did you know this?

Not at all

Perfectly

What are the six major steps of the viral lifecycle?

1) Attachment
2) Entry– getting past the cell membrane
3) mRNA production
4) Protein & genome synthesis
5) Virion assembly
6) Egress

Describe the process of attachment & entry of a virus into a host cell.

Attachment= Molecules on the exterior of the cell bind to the surface of the host cell (via receptors)
Entry= direct fusion or via high-jacking the receptor-mediated endocytosis pathway

How do dsDNA, ssDNA, dsRNA, +ssRNA, & -ssRNA differ in how they translate mRNA?

DsDNA= use cellular machinery to produce mRNA
ssDNA= use cellular DNA repair enzymes to produce dsDNA, then use RNA polymerase
+ssRNA=
○ Retrovirus use viral reverse transcriptase to make dsDNA
○ Others= use virus as mRNA
-ssRNA= need enzyme, viral RNA-dependent-RNA polyermase (RdRp) to make +mRNA
dsRNA also use RdRp

How do DNA viruses combat the fact that cellular DNA replication machinery is not available at all times?

dsDNA= often contain potent transcriptional activators that act as “turbo boosters”
encode own DNA replication machinery e.g. Herpes
encode proteins that push the cell into S-phase

How do + & -ssRNA viruses combat not having RdRp?

+ssRNA viruses encode a RdRp

- -ssRNA viruses encode & carry RdRp

What is the general pathway to viral assembly & egress?

1) Individual viral proteins form into capsid subunits
2) Subunits combine to form complete capsid
3) Viral genome and other essential virion components are selectively packaged into capsids
4) Exit

How does the egress of lytic viruses differ from non-lytic viruses?

Lytic= rupture the plasma membrane of infected cells & spill out, killing the host cell in the process
Non-lytic= egress without lysing

What are the mechanisms that pressure viruses to change & become more effective antigens?

- Point mutation - Recombination (DNA viruses only) ○ HSV - Reassortment (segmented) e.g. Influenza has 8 segments & after replication there can be a shuffling of segments-->dramatic changes in antigenicity

What is the difference between acute, chronic, & latent infection types?

Acute= virus killed off by immune system after infection & symptoms resolve - Common cold Chronic= infection followed by incomplete immune response (though asymptomatic, patients can infect other & are considered carriers) - Hepatitis Latent= starts similarly to acute & virus killed; however, virus goes dormant & is then reactivated - Herpes

How do viruses get into the body?

- Oral - Conjunctiva - Skin - Transplacental - Droplet - Direct inoculation (insect bite, trauma, injection) - Sexual transmission

How do viruses cause cellular injury?

Cytopathic effect

What is the cytopathic effect?

Structural changes in the host cells that are caused by viral invasion

What is a plaque assay?

Plaque assay= diagnostic technique using cytopathic effect - Infection leads to a "patch" or clearing or plaque - Note, 1 plaque= 1 virus-- quantification - ONLY way to determine INFECTIOUS virus

What is the only way to determine if a virus is infectious?

Plaque assay

What does a Plaque assay detect? What are the advantages & disadvantages of the technique?

``` Detects= Infectious virus Advantages= demonstrates active viral infection Disadvantages= restricted to viruses that replicate in culture & produce cytopathic effect ```

What does electron microscopy detect? What are the advantages & disadvantages of the technique?

``` Detects= Virion particles Advantages= Helpful in identification of emerging viruses Disadvantages= expensive & challenging ```

What does an ELISA assay detect? What are the advantages & disadvantages of the technique?

``` Detects= Viral proteins & glyocproteins Advantages= sensitive & quick Disadvantages= requires a specific antibody ```

What does PCR detect? What are the advantages & disadvantages of the technique?

``` Detects= DNA genomes Advantages= highly sensitive Disadvantages= DNA sequence information must be available ```

What does RT-PCR detect? What are the advantages & disadvantages of the technique?

``` Detects= RNA genomes Advantages= Highly sensitive Disadvantages= RNA sequence information must be available ```

What does a Western Blot detect? What are the advantages & disadvantages of the technique?

``` Detects= Anti-viral antibodies Advantages= sensitive & quick Disadvantages= - Time required for immune response - Difficult to differentiate present from past infections ```

What is a virion & what are the components of a virion?

Virion= a complete virus particle that consists of: 1) Nuclei acid genome 2) Capsid or protein coat

What is a nucleocapsid?

Capsid that lies interior to the lipid layer of an enveloped virus

In an enveloped virus, where does the lipid membrane come from?

Lipid membrane is derived from host membrane structures that are then modified by the virus

What is the only virus that is able to synthesize its own envelope?

Poxvirus

What is the difference between direct fusion & high-jacking the receptor mediated endocytosis pathway for entry?

Direct Fusion= - Enveloped virus ONLY - Viral proteins promote fusion with host cell membrane & capsid is released directly into cytoplasm - Fusion proteins remain embedded in membrane & can cause subsequent fusion reaction with neighboring cells High-jacking= - Enveloped or capsid virus - Using the receptor-mediated endocytosis pathway, plasma membrane around entire virion - If enveloped, viral & plasma membrane fuse prior to release of capsid into the cytoplasm

What are the steps of viral pathogenesis?

1) Host invasion 2) Primary viral replication 3) Spread 4) Cell injury 5) Host immune response 6) Viral clearance or establishment of chronic or latent infection