Flashcards in Lecture 10 Virology Deck (40)
What is a virion?
an individual virus
-non living, acellular, and metabolically inert
How do viruses differ from plasmids?
Plasmids have extracellular and intracellular forms
-viruses only have intracellular form
What composes virus structure?
-RNA or DNA
-Very small genome b/c it relies on host DNA
-protein shell protects genome
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
What are complex viruses?
virus with several parts with different symmetry
-eg. helical tail and icosahedral head = bacteriophage
What is the difference between naked and enveloped viruses?
naked = genome+capsid
Enveloped = contain an additional membrane
-common in animal viruses
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
What forms of life can viruses infect?
What is a sputnik virophage?
virus that infects other viruses in order to get into host cell
What role do viruses play in global ecology?
-Phagocytosed by macrophages
-cause cell lysis
How do we study viruses in the lab?
-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'
What are the steps of viral replication?
5. Release (lysis)
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
What is the viral replication step Penetration?
Bacterial Viruses (Bacteriophage)
-‐ (a) Attaches to Outer Membrane
-‐ (b) Retracts
-‐ (c) Contacts Cell Wall
-‐ (c) Releases Lysozyme
-‐ (c) Enters Cell through Cell Wall Hole
What is the viral replication step Synthesis?
1) Replicate the Viral Genome
2) Synthesize Proteins
What is the baltimore classification scheme?
Synthesis classification depends on type of viral genome
-DNA or RNA
-Double stranded or single stranded
How does synthesis differ for DNA viruses, RNA viruses, RNA retroviruses?
-dsDNA to mRNA to Protein
-ssDNA to dsDNA to mRNA to Protein
-ssRNA (+) = mRNA to Protein
-ssRNA (–) to mRNA to Protein
-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 to RNA
-RNA to DNA
What types of proteins do viruses synthesize in the synthesis step of viral replication?
– Aid Replication of Viral Genomes
– 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
-Cell Lysis = Virions Released
-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?
-virus genome in the host chromosome
-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?
-Cell Lysis = All Virions Released
-No Cell Lysis = Some Virions Bud
-No Viral Replication
-No Cell Lysis = No Virions Released
What steps of viral replication are targeted in ANTI-VIRAL mechanisms?
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