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Microbiology & Immunology > Viruses > Flashcards

Viruses Flashcards

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Biology 101 flashcards
1
Q

What is unique about viral replication compared to other pathogens?

A
  • Obligate Parasites: cannot replicate on their own, lack the machinery to repliate genome
  • Must infecy host to replicate
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2
Q

What are the key structural components of the viruses?

A
  • proteins
  • envelope
  • nucleic acids
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3
Q

Describe the types and characteristics of viral proteins.

A
  • Found in all viruses
  • Capsids
    • structural proteins
    • Icosahedra, Helical
  • Enzymes
  • M proteins
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4
Q

Describe the components of the enveloped vs. non-enveloped viruses.

A
  • enveloped
    • found only in some viruses
    • composed of lipids
    • makes virus susceptible to detergents
  • non-enveloped
    • glycoprotein layer
    • very hearty, resistant
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5
Q

What are the classifications of DNA viruses?

A
  • Enveloped
    • dsDNA (linear)
    • dsDNA (circular)
  • Non-enveloped
    • dsDNA (circular)
    • ssDNA (linear)
    • dsDNA (linear)
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6
Q

What are the classifications of RNA viruses?

A
  • Enveloped
    • retrovirus (+ssRNA —> DNA intermediate)
    • -ssRNA
    • +ssRNA
  • Non-enveloped
    • +ssRNA
    • dsRNA
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7
Q

What are the 7 virus types according to Baltimore Classification?

A
  1. Group I: dsDNA
  2. Group II: +ssDNA
  3. Group III: dsRNA
  4. Group IV: +ssRNA
  5. Group V: -ssRNA
  6. Group VI: +ssRNA (reverse transcription)
  7. Group VII: dsRNA (reverse transcription)
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8
Q

What are the goals of viral replication?

A
  1. make viral proteins
  2. duplicate viral genome
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9
Q

Where do RNA viruses generally replicate? Where do DNA viruses generally replicate?

A

RNA: cytoplasm

DNA: nucleus

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10
Q

Describe the major viral replication enzymes, their roles, and their sources.

A
  1. RNA-dependent RNA polymerase
    • ​​replicates RNA from RNA template
    • source: all RNA virses
  2. RNA-dependent DNA polymerase
    • ​reverse transcriptase, reverse transcribes RNA to DNA
    • source: virus
  3. DNA-dependent RNA polymerase
    • ​​transcribes RNA from DNA template
    • source: host
  4. DNA polymerase
    • ​​replicates DNA from DNA
    • source: host/virus
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11
Q

What are the steps in the viral replication cycle?

A
  1. attachment & entry into host cell
  2. viron uncoating
  3. transcription of viral mRNA
  4. translation of viral mRNA (viral protein production)
  5. replication of viral genome
  6. assembly of virons (viral proteins encapsulate viral genes)
  7. virons released from host cell via budding or lysis
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12
Q

What do all viruses transcribe before protein translation?

A

mRNA (+ssRNA)

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13
Q

What is the general process of viral protein synthesis?

A

**General Process: **Viral DNA/RNA –> mRNA –> proteins

Exception: Viral RNA retrovirus –> DNA –> mRNA –> proteins

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14
Q

+ssRNA replication

A
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15
Q

-ssRNA replication

A
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16
Q

dsRNA replication

A
17
Q

RNA retrovirus replication

A
18
Q

dsDNA retrovirus replication

A
19
Q

ssDNA replication

A
20
Q

dsDNA replication

A
21
Q

What is cytopathic effect (CPE)?

A

morphological changes that occur in cells during many viral infection: ballooning, rounding, lysis, giant cell (syncitium), or inclusion body formation

22
Q

What is Viral Latency?

A
  • virus becomes dormant and ceases production of new virus to hide from immune system
  • virus can reactivate at any time, life-long persistence
  • ex. herpes simplex virus
23
Q

What is viral tropism?

A

specificity of a virus for a specific host tissue; determined by interaction between host cell receptors and viral glycoproteins

24
Q

How does viral genome size determine pathogenesis?

A
  • size of genome determines how many proteins it can make to take over the host cell
  • small viral genome: less flexible in cell targeting; may not have division machinery, must rely on host cell’s machinery
    • parovirus B19
  • large viral genome: more flexible in cell targeting, carry genes for replication machinery
25
Q

Cytopathic Effects: enveloped vs. naked

A
  • non-enveloped naked: more virulent, cause cell lysis and killilng
  • eveloped: less virulent, can bud off of cell
    • synctia formation
    • hemogglutination
26
Q

Define Syncytia formation.

A
  • viral protein spikes get expressed on host cell membrane when enveloped virus buds of; causes host cells to fuse with each other & create a giant cell
  • occurs when viruses enter via pH-independent membrane fusion
27
Q

Define hemagglutination formation.

A
  • viral docking proteins get expressed on surface of host RBC; multiple RBCs cannot fuse like syncytia but then can cross-link and stay aggregated
  • occurs when viruses enter via pH-dependent membrane fusion
28
Q

What is antigenic shift?

A
  • form of viral diversity
  • occurs as a result of segmented and rearrangeable genome which means the docking proteins it uses can change quite rapidly
  • ex. influenza- can infect multiple organisms, changes frequently
29
Q

What is antigenic drift?

A
  • form of viral diversity
  • occurs as a result of mutations introduced by RNA-dependent RNA polymerase during replication (lacks proofreading mechanism, introduces errors)
30
Q

Why must -ssRNA use their own RNA-dependent RNA Polymerase to synthesize its +ssRNA for use in translation?

A

**host doesn’t make RNA-dependent RNA Polymerase

31
Q

What are the 3 different routes of viral infection/dissemination?

A
  1. accute infection
  2. chronic infection
  3. latent infection
32
Q

What occurs in an acute viral infection (use example)?

A
  • EXAMPLE: Poliovirus (enterovirus)
  1. virus enters the cell
  2. travels and replicates at primary sites (LNs)
  3. dimmeniates causing viremia
  4. infects at secondary replication sites (nervous system)
  5. spreads to other hosts (i.e. fecal-oral)
33
Q

What occurs in an chronic viral infection (use example)?

A
  • EXAMPLE: HIV
  1. acute infection
  2. chronic lymphadenopathy
  3. sub-clinical immune dysfunction
  4. skin, mucous membrane immune defects
    • CD4 T cell decline
  5. systemic innume deficiency
    • Anti-HIV antibodies decrease, viral load increases
34
Q

What occurs in a latent viral infection (use example)?

A
  • EXAMPLE: HSV
  1. viruses can remain dormant and undetected in cell as episome or provirus
    • episome: circular DNA containing viral genome
    • provirus: viral genome integrates into host chromosome
  2. herpes: latent form resides in neurons as episome; reactivated by stress
35
Q

How are viral PAMPs recognized by host immune system?

A
  • PRRs on host cells detect PAMPs
  • ex. dsRNA detected by TLR3, TLR 7/8, RIG-I
36
Q

How does innate immune system respond to viruses?

A
  • infected cells release IFN that activate macs and NKs
37
Q

How does adaptive immune system respond to viruses?

A
  • CTLs target cells w/ MHC-I + virgal antigen
38
Q

What are the host immunopathologies associated with viral infection? Examples?

A
  • IFN: fever, muscle ache, flu symptoms (i.e. influenza)
  • CTL: can destroy normal tissue (i.e. liver in HPV)
  • CD4+: delayed-type hypersensitivity can cause rashes (i.e. measles & mumps)
  • Abs: immune complex hypersensitivity, complement activation, tissue damage (i.e. HBV)
  • Chronic inflammation: if viral infection cannot be contained

Microbiology & Immunology (7 decks)

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