Exam #1: Medical Virology Flashcards Preview

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Flashcards in Exam #1: Medical Virology Deck (43):
1

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

2

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

3

What is the matrix or tegument of a virus?

Space between the capsid & envelope

4

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

5

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

6

How are viruses classified?

- Genome (which tells how the virus replicates)
- Class of disease caused

7

What family of viruses contains ssDNA?

Paroviridae

8

What families of viruses contains dsDNA?

Papovaviridae
Adenoviridae
Herpesviridae
Poxviridae
Hepadnaviridae

9

What is the family of dsRNA viruses?

Revoviridae

10

What are the families of -ssRNA viruses?

Orthomyxoviridae
Paramyxoviridea
Rhabdoviridae
Bunyaviridae
Arenaviridae
Filvoiridae

11

What are the families of +ssRNA viruses?

Togaviridae
Flavaviridae
Coronaviridae
Retroviridae
Picornaviridae
Caliviridae
Hepeviridae

12

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

13

What are the three major forms of capsids?

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

14

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

15

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

16

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)

17

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

18

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

19

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

20

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

21

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

22

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

- +ssRNA viruses encode a RdRp
- -ssRNA viruses encode & carry RdRp

23

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

24

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

25

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

26

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

27

How do viruses get into the body?

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

28

How do viruses cause cellular injury?

Cytopathic effect

29

What is the cytopathic effect?

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

30

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

31

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

Plaque assay

32

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

33

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

34

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

35

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

36

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

37

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

38

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

39

What is a nucleocapsid?

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

40

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

41

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

Poxvirus

42

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

43

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

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