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
What are the similarities of animal/bacterial viruses?
- capsids + DNA/RNA genome
- Infection and takeover of host
- assembly and release
What are the differences of animal/bacterial viruses?
- entire virion enters animal cell
- eukaryotic cell contains nucleus + site reproduction
- viroplasms form in some eukaryotic cells to increase virion assembly rate.
What are the outcomes of virulent infections?
- Transformation: normal cell - tumor cell
- Persistent: slow release of virions from host cell (no lysis)
- latent infection: viral DNA exists in host genome as provirus (not active till triggered)
What is a retrovirus?
enveloped virion that contains two ss(t) RNA genome
Role of reverse transcriptase?
synthesize DNA from RNA
Role of ribonuclease activity?
degrades RNA strands to DNA hybrid
Role of DNA polymerase?
makes dsDNA from ssDNA using viral tRNA
Role of integrase?
integrates dsDNA into genome
