Lec 62: Basic Virology

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

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