Viruses

Question 1

What is unique about viral replication compared to other pathogens?

Answer 1

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

Question 2

What are the key structural components of the viruses?

Answer 2

• proteins
• envelope
• nucleic acids

Question 3

Describe the types and characteristics of viral proteins.

Answer 3

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

Question 4

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

Answer 4

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

Question 5

What are the classifications of DNA viruses?

Answer 5

• Enveloped
  
  • dsDNA (linear)
  • dsDNA (circular)
• Non-enveloped
  
  • dsDNA (circular)
  • ssDNA (linear)
  • dsDNA (linear)

Question 6

What are the classifications of RNA viruses?

Answer 6

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

Question 7

What are the 7 virus types according to Baltimore Classification?

Answer 7

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)

Question 8

What are the goals of viral replication?

Answer 8

1. make viral proteins
2. duplicate viral genome

Question 9

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

Answer 9

RNA: cytoplasm

DNA: nucleus

Question 10

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

Answer 10

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

Question 11

What are the steps in the viral replication cycle?

Answer 11

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

Question 12

What do all viruses transcribe before protein translation?

Answer 12

mRNA (+ssRNA)

Question 13

What is the general process of viral protein synthesis?

Answer 13

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

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

Question 14

+ssRNA replication

Answer 14

Question 15

-ssRNA replication

Answer 15

Question 16

dsRNA replication

Answer 16

Question 17

RNA retrovirus replication

Answer 17

Question 18

dsDNA retrovirus replication

Answer 18

Question 19

ssDNA replication

Answer 19

Question 20

dsDNA replication

Answer 20

Question 21

What is cytopathic effect (CPE)?

Answer 21

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

Question 22

What is Viral Latency?

Answer 22

• 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

Question 23

What is viral tropism?

Answer 23

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

Question 24

How does viral genome size determine pathogenesis?

Answer 24

• 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

Question 25

Cytopathic Effects: enveloped vs. naked

Answer 25

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

Question 26

Define Syncytia formation.

Answer 26

* 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

Question 27

Define hemagglutination formation.

Answer 27

* 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

Question 28

What is antigenic shift?

Answer 28

* 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

Question 29

What is antigenic drift?

Answer 29

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

Question 30

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

Answer 30

\*\*host doesn't make RNA-dependent RNA Polymerase

Question 31

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

Answer 31

1. accute infection 2. chronic infection 3. latent infection

Question 32

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

Answer 32

* 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)

Question 33

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

Answer 33

* 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

Question 34

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

Answer 34

* 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

Question 35

How are viral PAMPs recognized by host immune system?

Answer 35

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

Question 36

How does innate immune system respond to viruses?

Answer 36

* infected cells release IFN that activate macs and NKs

Question 37

How does adaptive immune system respond to viruses?

Answer 37

* CTLs target cells w/ MHC-I + virgal antigen

Question 38

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

Answer 38

* 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