chapter 5 - viruses Flashcards
What is a virus
genetic element that can only multiply in a host cell
What are viral components of a naked particle
nucleic acids and capsid
What are viral components of a enveloped virus
glycoprotein, nucleocapsids and envelope
What are the two modes of infection?
virulent: gets into cell, makes copies, then bursts
lysogenic: gets in cell, stays in genome and comes out when it wants
What is a virion?
extracellular form of a virus, facilitates transmission
What is a capsomere
protein molecules arranged around nucleic acid making capsule capsids
What are the two basic virus symmetry?
helical: rod shaped, length determines by nucleic acid, width is the size of capsomere.
Icosahedral: spherical, requires few capsomere
What does structural integrity mean
provides structure and shape
What does the complex viral structure intel?
- head (contains DNA)
- collar
- tail
- tail fibers
What are the enzymes inside virions and what are their roles?
- lysozymes: makes hole in the bacteria to allow entry of nucleic acid
- neuraminidase: destroys glycoproteins/lipids and allows liberation of viruses.
What are the two types of nucleic acid polymerases?
- RNA replicase: RNA-dependent RNA polymerase
- Reverse transcriptase: RNA-dependent DNA polymerase in retrovirus
What are enveloped viruses?
nucleocapsid surrounded by lipoprotein membrane, use outer surface proteins to attach/insert.
What is a plaque assay?
clear zones of cell lysis that developed on lawns of host cells where successful viral infections occur
What is a titer?
number of infectious virions per volume of liquid
What are the three steps of culturing viruses?
- cell-phage mixture is poured onto a solidified nutrient agar plate.
- mixture is left to solidify
- incubation allows bacterial growth and phage reproduction
What is plating efficiency?
estimates of viral titer by plaque assay
What are the 5 steps of the replication cycle of prokaryotic viruses?
- Attachment: absorption of virus
- Penetration: entry/injection of viral nucleic acid
- Synthesis: of viral nucleic acid + proteins by host cell as redirected virus
- Assembly: of capsids + packaging of viral genomes into new virions
- Release: of new virions from host.
What is the eclipse phase?
genome replicated + proteins synthesized
What is the maturation phase?
packaging nucleic acids in capsids (proteins being made)
What is the latent period?
eclipse + maturation phase
What does burst size mean?
number of virions released
During virions synthesis, what proteins are needed?
- Early proteins: enzymes needed for DNA replication + proteins that modify host enzyme
- Middle + late proteins: head + tail proteins and enzymes required to liberate mature phages
What are the 3 stages of packaging virions?
- Prohead gets assembled
- Motor assembles
- Genome gets pumped into prohead using ATP
What are the two pathways in temperate bacteriophages?
- Lytic Pathway
- after attachement/injection, lytic events are initated
- phage synthesized and virions assemble
-lysis of host cell, release of new virion - Lysogenic Pathway
- after attachment/injection, viral DNA is integrated into host DNA
-cell becomes lysogenized
- viral DNA replicated with host DNA
- prophage is created
