Lecture 10 Virology Flashcards by Stephen McCartney

What is a virion?

an individual virus

-non living, acellular, and metabolically inert

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How do viruses differ from plasmids?

Plasmids have extracellular and intracellular forms

-viruses only have intracellular form

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What composes virus structure?

Genome

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

Capsid
-protein shell protects genome

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What kind of structure do viral capsids have?

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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What are complex viruses?

virus with several parts with different symmetry

-eg. helical tail and icosahedral head = bacteriophage

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What is the difference between naked and enveloped viruses?

naked = genome+capsid

Enveloped = contain an additional membrane

surrounds nucleocapsid
common in animal viruses

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Why would some virions contain enzymes?

For functions not provided by host cells

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

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What forms of life can viruses infect?

Prokaryotes

bacteriophage
archaeal viruses

Eukaryotes

Other viruses
-virophages

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What is a sputnik virophage?

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

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What role do viruses play in global ecology?

Viral shunt

Phagocytosed by macrophages
cause cell lysis
food chain

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How do we study viruses in the lab?

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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What are the steps of viral replication?

Attachment
Penetration
Synthesis
Assembly
Release (lysis)

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What is the viral replication step attachment?

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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What is the viral replication step Penetration?

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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What is the viral replication step Synthesis?

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

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What is the baltimore classification scheme?

Synthesis classification depends on type of viral genome

DNA or RNA
Double stranded or single stranded

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

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

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

Part of the synthesis step to replicate viral genome

RNA-dependent RNA Polymerase

RNA Replicase
RNA to RNA

Reverse Transcriptase
-RNA to DNA

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

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

What is the viral replication step Assembly?

Nucleocapsids Formed By Self-‐Assembly

What is the viral replication step Release?

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

What is the bacteriophage lambda?

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

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

Prophage
-virus genome in the host chromosome

Lysogen
-bacterial cell with viral genome

What is the ecological significance of lysogenic pathway?

New genetic properties

immunity to related viruses

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

Naked viruses = bacteriophages Enveloped viruses = animals

What are the key differences of animal viruses from bacterophages?

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

What are the types of animal viruses?

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

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

Attachment Penetration Synthesis If it gets to Assembly or Release then its too late

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

NEARLY Impossible to Prevent - Viruses Attached to Surface Receptors of Host Cells - Same Receptors Needed for Normal Cell Functioning

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

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

What are restriction endonucleases?

Only in Prokaryotes Recognize and Digest Foreign DNA Cut DNA at Specific Nucleotide Sites

What is CRISPR?

Prokaryote anti viral mechanism - Clustered Regularly Interspaced Short Palindromic Repeats (Viral Sequence “Archive”) - only in prokaryotes

What is RNAi?

RNA interference - identifies dsRNA which is only in viruses - cuts dsRNA into pieces - uses pieces to target/destroy viral mRNA

What are subviral entities? What are the types?

Infectious agents that resemble viruses Defective viruses Viroids Prions

What are defective viruses?

Subviral entity that Cannot Infect Host Cells Alone - Rely on Helper Viruses - Helper Viruses Can be the Same Type of Virus or Completely Unrelated

What are satellite viruses?

type of defective virus that is not a fully functional virus | -rely completely on unrelated helper viruses

What are Viroids?

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

What are prions?

subviral entity with infectious protein molecules - unlike viruses they have no DNA/RNA - misfolded proteins - found in animals

What are the types of prions?

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

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

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

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Lecture 10 Virology Flashcards

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