OBJ - Basic Virology

Question 1

Virus

Answer 1

• Very small in size
• Obligate parasites - Lack key elements for self-propagation
• Viruses cannot affect ALL cells, need right combo

Proteins (all viruses)
• Capsid/Matrix proteins - Icosahedral or helical based on shape of capsomeres
• Enzymes/Other proteins
- M proteins
- Enzymes (ploymerase, integrase, etc)
- Complex viruses encode for a large array of proteins

Nucleic acids (all viruses) - RNA/DNA
- RNA:
      \+ssRNA (positive single strand)
      -ssRNA
      dsRNA
- DNA:
      dsDNA
      ssDNA

Envelope (only some viruses)
• Lipids - Phospholipid bilayer
• No envelope = “naked” - GI tract viruses (10-15 particles to infect whole cruise ship)

Question 2

Central Dogma in Molecular Biology

Answer 2

make proteins from translating RNA/DNA

Question 3

Virus Classification

Answer 3

How they make mRNA & then proteins

Group 1 = dsDNA -> mRNA
Group 2 = +ssDNA -> dsDNA -> mRNA
Group 3 = dsRNA -> mRNA
Group 4 = +ssRNA -> -ssRNA -> mRNA
Group 5 = -ssRNA -> mRNA
Group 6 = +ssRNA with Reverse Transcription -> dsDNA intermediate -> mRNA
HIV -> make DNA intermediate to make mRNA
Group 7 = dsDNA with Reverse Transcription -> dsDNA intermediate -> mRNA

**ss need to make complementary strands (- -> + or + -> -) to make mRNA

Envelope/Non-Enveloped then by their type of DNS

Question 4

Viral replication cycle

Answer 4

RNA = replicate in Cytoplasm
DNA & Reverse Trasncriptase viruses = replicate in nucleus

1) Attachment - highly specific
i. e. HIV can only enter cells with CD4+
- Must first bind to cell surface

2) Entry
- Direct Penetration - inject Nucleic Acid from capsid
- Membrane fusion -
- Endocytosis - inside vessicles & then released/uncoated

3) Uncoating

4) Synthesis of Proteins & Nucleic Acids
- Viral Protein Synthesis - All viruses transcribe mRNA that is translated to proteins by cells’ machinery
- Viral Genome Synthesis via polymerases/reverse trasncriptases

5) Assembly

6) Release
- Enveloped - migrate to surface of cell & use budding to pinch off & release
- Nonenveloped = cell lysis

Question 5

Retroviruses

Answer 5

RNA retrovirus:
starts with RNA
converts to DNA
to make RNA

DNA retrovirus:
starts with DNA
converts to RNA
to make DNA

Question 6

Cytopathic Effect (CPE)

Answer 6

Morphological changes in cells such as
the ballooning or rounding or lysis or giant cell (syncytium) formation, inclusion bodies, etc.

Inclusion bodies = aggregated proteins located in:
DNA = nucleus
RNA = cytoplasm

Question 7

Latency

Answer 7

• Virus becomes dormant and ceases production of new virus; viral proteins are not made and expressed
• Infected cells hide from the immune system leading to life-long persistence (proteins aren’t made so aren’t expressed on cells/MHC I’s so CTL can’t attack)

Consequence:
Virus can reactivate any time leading to active infection

Question 8

Tropism

Answer 8

The affinity for specific cells -> so system/species specific

Expression of Receptor Determines Tropism

Question 9

Viral protein synthesis

Answer 9

Major enzymes:
1. RNA-dependent RNA polymerase = Replicates RNA from RNA template
Source: all RNA viruses

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