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BIO 425: Microbiology > Lecture 10 Virology > Flashcards

Lecture 10 Virology Flashcards

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1
Q

What is a virion?

A

an individual virus

-non living, acellular, and metabolically inert

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2
Q

How do viruses differ from plasmids?

A

Plasmids have extracellular and intracellular forms

-viruses only have intracellular form

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3
Q

What composes virus structure?

A

Genome

  • RNA or DNA
  • Very small genome b/c it relies on host DNA

Capsid
-protein shell protects genome

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4
Q

What kind of structure do viral capsids have?

A

Composed of protein molecules in repetitive pattern

  • single or multiple protein types = capsomere
  • the protein arrangement determines shape

Icosahedral symmetry = spherical virus
Helical symmetry = rod shaped virus

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5
Q

What are complex viruses?

A

virus with several parts with different symmetry

-eg. helical tail and icosahedral head = bacteriophage

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6
Q

What is the difference between naked and enveloped viruses?

A

naked = genome+capsid

Enveloped = contain an additional membrane

  • surrounds nucleocapsid
  • common in animal viruses
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7
Q

Why would some virions contain enzymes?

A

For functions not provided by host cells

  • lysozymes for invasion of host cell
  • viral replication of RNA = reverse transcriptase
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8
Q

What forms of life can viruses infect?

A

Prokaryotes

  • bacteriophage
  • archaeal viruses

Eukaryotes

Other viruses
-virophages

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9
Q

What is a sputnik virophage?

A

virus that infects other viruses in order to get into host cell

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10
Q

What role do viruses play in global ecology?

A

Viral shunt

  • Phagocytosed by macrophages
  • cause cell lysis
  • food chain
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11
Q

How do we study viruses in the lab?

A

Plaque assay
-used to quantify viruses

the plate completely covered with bacterial colony

  • the number of holes that form = number of viruses
  • the virus lyses bacterial cells forming ‘plaques’
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12
Q

What are the steps of viral replication?

A
  1. Attachment
  2. Penetration
  3. Synthesis
  4. Assembly
  5. Release (lysis)
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13
Q

What is the viral replication step attachment?

A

Proteins on virion capsid bind surface receptors on host cell

If the host doesn’t have right receptors then virion can’t bind = specificity

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14
Q

What is the viral replication step Penetration?

A 
Bacterial Viruses (Bacteriophage)
·∙
Tail Fibers
-­‐ (a) Attaches to Outer Membrane
-­‐ (b) Retracts
·∙
Tail Core
-­‐ (c) Contacts Cell Wall
-­‐ (c) Releases Lysozyme
·∙
Viral DNA
-­‐ (c) Enters Cell through Cell Wall Hole
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15
Q

What is the viral replication step Synthesis?

A

Two Steps:
·∙
1) Replicate the Viral Genome
2) Synthesize Proteins

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16
Q

What is the baltimore classification scheme?

A

Synthesis classification depends on type of viral genome

  • DNA or RNA
  • Double stranded or single stranded
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17
Q

How does synthesis differ for DNA viruses, RNA viruses, RNA retroviruses?

A

DNA Viruses

  • dsDNA to mRNA to Protein
  • ssDNA to dsDNA to mRNA to Protein

RNA Viruses

  • ssRNA (+) = mRNA to Protein
  • ssRNA (–) to mRNA to Protein

RNA Retroviruses
-ssRNA (+) to dsDNA to mRNA to Protein

18
Q

What is RNA-dependent RNA Polymerase and what is Reverse transcriptase?

A

Part of the synthesis step to replicate viral genome

RNA-dependent RNA Polymerase

  • RNA Replicase
  • RNA to RNA

Reverse Transcriptase
-RNA to DNA

19
Q

What types of proteins do viruses synthesize in the synthesis step of viral replication?

A 
·∙Early Proteins
– Aid Replication of Viral Genomes
·∙
Late Proteins
– Aid Construction of Viral Capsid
20
Q

What is the viral replication step Assembly?

A

Nucleocapsids Formed By Self-­‐Assembly

21
Q

What is the viral replication step Release?

A 
Depends on Viral Life Cycle
·∙
Lytic (Virulent) Mode
-­‐ Host cells lysed and killed
·∙
Lysogenic (Temperate) Mode
-­‐ Host cells remain intact
22
Q

What is the bacteriophage lambda?

A

Two pathways of viral replication in bacteria

Lytic Pathway

  • Viral Replication
  • Cell Lysis = Virions Released

Lysogenic Pathway

  • Viral DNA to Host DNA
  • Replicates with Host Cell

When jump from lysogenic to lytic pathway called induction

23
Q

In the lysogenic pathway, what is a prophage and what is a lysogen?

A

Prophage
-virus genome in the host chromosome

Lysogen
-bacterial cell with viral genome

24
Q

What is the ecological significance of lysogenic pathway?

A

New genetic properties

immunity to related viruses

25
Q

What kinds of viruses infect bacteria and what kind infect animals?

A

Naked viruses = bacteriophages

Enveloped viruses = animals

26
Q

What are the key differences of animal viruses from bacterophages?

A 
Entire Virion Enters the Host Cell
·∙
Virion Must Enter the Nucleus
·∙
Virion Can Exit without Cell Lysis (“Budding”)
27
Q

What are the types of animal viruses?

A

Virulent Infections

  • Viral Replication
  • Cell Lysis = All Virions Released

Persistent Infections

  • Viral Replication
  • No Cell Lysis = Some Virions Bud

Latent Infections

  • No Viral Replication
  • No Cell Lysis = No Virions Released
28
Q

What steps of viral replication are targeted in ANTI-VIRAL mechanisms?

A

Attachment
Penetration
Synthesis

If it gets to Assembly or Release then its too late

29
Q

What are the mechanisms of anti-viral defense for attachment?

A

NEARLY Impossible to Prevent

  • Viruses Attached to Surface Receptors of Host Cells
  • Same Receptors Needed for Normal Cell Functioning
30
Q

What are the mechanisms of anti-viral defense for synthesis?

A 
Target and Destroy Viral Genome
-Restriction Endonucleases 
-RNA-­‐Based Defense Systems
·∙
CRISPR (prokaryotes)
-Interference RNA (eukaryotes)
31
Q

What are restriction endonucleases?

A

Only in Prokaryotes

Recognize and Digest Foreign DNA

Cut DNA at Specific Nucleotide Sites

32
Q

What is CRISPR?

A

Prokaryote anti viral mechanism

  • ­Clustered Regularly Interspaced Short Palindromic Repeats (Viral Sequence “Archive”)
  • only in prokaryotes
33
Q

What is RNAi?

A

RNA interference

  • identifies dsRNA which is only in viruses
  • cuts dsRNA into pieces
  • uses pieces to target/destroy viral mRNA
34
Q

What are subviral entities? What are the types?

A

Infectious agents that resemble viruses

Defective viruses
Viroids
Prions

35
Q

What are defective viruses?

A

Subviral entity that Cannot Infect Host Cells Alone

  • Rely on Helper Viruses
  • Helper Viruses Can be the Same Type of Virus or Completely Unrelated
36
Q

What are satellite viruses?

A

type of defective virus that is not a fully functional virus

-rely completely on unrelated helper viruses

37
Q

What are Viroids?

A

Subviral entity with Infectious RNA molecules

  • have no capsid
  • found only in plants
  • high degree of secondary structure
  • enter host through wounds
  • have no protein encoding genes
38
Q

What are prions?

A

subviral entity with infectious protein molecules

  • unlike viruses they have no DNA/RNA
  • misfolded proteins
  • found in animals
39
Q

What are the types of prions?

A

Native Prion Proteins (PrPC)
-Present in Neurons of Healthy Animals

Misfolded Prion Proteins (PrPSC)

  • Present in Diseased Animals
  • Same Amino Acid Sequence as PrPC,
  • Different Structural Conformation
40
Q

What are the effects of misfolded protein conformations caused by prions?

A

Resistant to Proteases (degradation)
·∙
Becomes Insoluble (aggregates in neurons)
·∙
Induces Misfolding of Native Proteins (“replication”)

BIO 425: Microbiology (22 decks)

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