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Fundamentals I > DNA Viruses > Flashcards

DNA Viruses Flashcards

1
Q

What is the only family of DNA viruses that is not icosahedral?

A

Pox viruses

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2
Q

What is the genomic composition of herpes virus?

A

enveloped dsDNA linear; it circularizes during latency and replication

lytic type

**All herpes viruses establish a latent infection and reactivate under various conditions

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3
Q

what 3 families of DNA viruses have envelopes?

A

Pox, hepadnavirus, and herpesvirus

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4
Q

What is the genomic composition of hepadnaviruses?

A

partial dsDNA: nicked circle formation with positive strand only in regions of overlap

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5
Q

Where do DNA viruses replicate? What is the one exception?

A

In the nucleus; exception - poxvirus

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6
Q

What 3 strategies do DNA viruses use to maximize their genome?

A

Multiple promoters
Alternative splicing
Code from both strands (exception: papilloma codes from only one strand)

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7
Q

What is the hallmark of DNA viruses?

A

Distinct replication phases and reproducible patterns of expression for viral genes and viral DNA syntheses - not chaotic

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8
Q

4 justifications for synchronized replication phases

A

Prepare host environment
Diminish competition of low expression viral genes (regulatory factors) with high expression genes (structural proteins)
Avoid premature cytopathic effects
Help avoid immune detection

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9
Q

What gene are expressed in immediate early expression?

A

Regulatory proteins for replication (transcription factors, transactivators)

  • do not require any new protein synthesis for expression
  • use transcription factors carried in parental virion or host factors
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10
Q

What genes are expressed in early gene expression?

A

Regulatory proteins that actually participate in viral replication (think enzymes: helicase, DNA polymerase etc.)

-targets for antiviral therapy

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11
Q

What genes are expressed in late gene expression? What is notable about this stage?

A

Structural proteins for assemblying mature virions

Both parental and progeny DNA is used as template bc so much protein needs to be made: structural, not enzymatic

Not expressed until after initiation of viral DNA synthesis

Requires a shift: downregulate early gene expression except for DNA synthesis

When cytopathic effects (like inclusion bodies and syncytia) occur

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12
Q

Name the 2 versions of viral DNA synthesis with examples.

A

Host DNA polymerase mediated: replication uses host cell polymerases (Papilloma, Parvo)

Viral polymerase mediated: virus encodes its own polymerases and can inhibit action of host polymerases (Adeno, Herpes, Pox)

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13
Q

What are 2 draw backs to host DNA polymerase-mediated replication?

A

Host cell must be in S phase (dividing cells)
-some viruses encode proteins that induce cell to enter dividing state

Some viral proteins neutralize tumor suppressor factors so cause a transforming infection –> promotes cell proliferation but can also be oncogenic

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14
Q

What is a transforming infection?

A

Infection where cell proliferation is induced by turning off tumor suppressors and up-regulating growth factors, thereby leading to cancer

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15
Q

Name the 4 viral synthesis mechanisms with examples

A

1) Self priming (parvo)
2) Bi-directional (papovavirus)
3) Strand displacement (adenoviruses)
4) Rolling Circle (Herpes Virus)

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16
Q

What do self-priming viruses require?

A

an inverted terminal repetition (ITR) for 3’ OH hairpin formation

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17
Q

What does rolling circle replication require?

A

3’ OH nick and viral primases (RNA primers)

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18
Q

What is significant about inclusion bodies?

A

Site of viral DNA synthesis and virus packaging

19
Q

Describe acute infection

A

Viruses infect, rapidly replicate and are cleared by the host
High yield of virus
Host cell is completely permissive of infection
Usually result in dramatic CPE and cell lysis
Time scale of days
Ex: adenovirus

20
Q

Describe persistent infection

A

Infection is not cleared efficiently by the adaptive immune response –> continuous or intermitten virus production

Virus remains in primary target organ or distal site

Time scale of months - lifetime

21
Q

Describe chronic infection

A

Type of persistent: continuous production of low/moderate levels of virus

Ex: Hep B, HIV

22
Q

Describe Latent Infection

A

Type of persistent: viral genome is maintianed in host with little or no viral gen expression

**No virus produced during latent stage

Ex: herpes

23
Q

Describe slow infection

A

Type of persistent: long incubation period with low/undetectable virus

ex: polyoma JC

24
Q

What is viral reactivation?

A

When latent virus is induced to begin lytic replication

25
Q

What is the infection course of herpes simplex virus?

A

1) infection of epithelial cells and release of progeny
2) Infection of sensory ganglion
3) Gene expression repressed; genome maintained in nucleus of neuron
4) Reactivation of latent viral genome by stress –> production of new virus
5) Spread back to mucosal surface and re-infect epithelial cells

**sometimes herpes spreads to CNS: lethal

26
Q

Describe abortive infection

A

Virus infects cells, may express some genes but fails to produce progeny virus

CPE and transformation of host cell can still occur

NOT the same as asymptomatic infection

27
Q

2 basic stages from normal cell to malignant cancer

A

1) Immortalization: can be achieved by viral transformation

2) Additional changes that make immortal cells malignant

28
Q

Describe basic features of Parvovirus family and give examples

A

Linear ssDNA; naked
-insufficient DNA so requires helper virus or rapidly dividing cells

Ex: Dependovirus most co-infect with adenovirus - doesn’t cause disease (useful mode of drug admin?)

Parvo B19 requires dividing cells; causes erythema infectiosum, aplastic anemia and fetal loss

29
Q

Describe basic features of Papovavirus family and give examples

A

circular dsDNA, naked, icosahedral

Can persist in integrated (polyoma) or episomal form (papilloma)
Release by lysis
Only human hosts
Papilloma restricted to differentiatign cels
Multiple splicing events and promoters

EX: HPV: causes cervical cancer and warts; most common STD in US (20M)

30
Q

What 3 types of HPV cause cervical cancer?

A

16, 18, 31

31
Q

What types of HPV are prevented by the vaccine?

A

6, 11, 16, and 18

32
Q

Describe the 4 stages of papilloma infection

A

1) Abrasion allows virus to infect basal epithelial cells (skin precursor)
2) Amplification of episomal DNA
3) Maintenance replication in differentiating cells
4) Productive viral replication ONLY in differentiated cells

33
Q

3 examples of polyoma viruses and their associated diseases

A

MCV: merkel cell sarcoma

BK: renal disease and hemorrhagic cysts

JCV: progressive multifocal leukoencephalopathy

34
Q

Describe basic features of Adenovirus family and give examples

A

linear dsDNA; naked

transmitted via respiratory or ocular droplets
Causes respiratory disease, conjunctivitis, hemorrhagic cysts
Can be used as viral vecto for gene therapy

35
Q

HSV 1& 2 (HCV 1&2)

A

Cold sores, genital herpes and encephalitis

36
Q

HHV3

A

Varicella Zoster - chicken pox, shingles

37
Q

HHV 4

A

Epstein barr - mono, nasopharyngeal carcinoma, Burkitt’s lymphoma

38
Q

HHV5

A

CMV - birthd defects, retinitis, reactivation in immunosuppressed individuals

39
Q

HHV6

A

Roseola infantum - high fever and rash

40
Q

HHV8

A

Kaposi’s sarcoma associated
Body cavity based lymphoma (primary effusion lymphoma)
Multicentric Castleman’s disease

41
Q

What makes acyclovir safe for treatment of HSV 1 and 2 and HHV3?

A

It’s a prodrug that requires metabolism by viral thymidine kinase to be active

Acts as guanine nucleotide analog that terminates DNA synthesis due to lack of 3’OH

42
Q

Describe basic features of Hepadnaviruses including examples

A

Mixed ss and ds DNA; enveloped

Complex replication cycle includes reverse transcriptase step (retroid)
Tropism restricted to liver cells
Blood-blood or sexual transmission
occupation risk of health care workers
incubates for ~90 days
Can be cleared or persistent infection –> cirrhosis, primary hepatocellular carcinoma
effective vaccine available

43
Q

Describe basic features of the pox virus

A

Largest genome of any human virus
Enveloped, linear dsDNA
Replicates in the cytoplasm: encodes everythign it needs

Ex: variola and vaccinia

Fundamentals I (4 decks)

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