Lecture 6 Flashcards
What are 3 qualities of living cells that viruses posses?
1) replicate
2) mutate
3) recombine
Why are viruses not cells?
1) depend on cells to reproduce
2) don’t contain ribosomes so they can’t make proteins independently
What are viruses that infect bacteria called?
phages
What are the 2 viral life cycles?
lytic or lysogenic
How does the lysogenic cycle work?
host cell doesn’t die and the virus or phage is transmitted to daughter cells
Why cycle contributes to genetic diversity to the host?
lysogenic, adds new traits/DNA
How do viruses differ? (4)
1) size
2) shape
3) genetic makeup (ssDNA, dsDNA, ssRNA, dsRNA)
4) shell structure (enveloped vs non-enveloped)
What is the basic structure of a virus?
nucleic acids within a protein shell capsid
What is the capsid made of? shapes? special quality?
capsomers
shapes: icosahedron or helical
can self assemble
Structure of capsid assembly?
capsomers are asymmetric,
3 in each face and 20 faces per virion for icosahedral
What is the capsid surrounded by in enveloped viruses? where do they get these components?
lipid-carbohydrate-protein envelope
lipid and carbohydrates = host membranes
proteins = virus
What is the purpose of spikes?
attachment to host cells
How do pages insert their nucleic acids?
tail fiber and base plate attache to host by binding to LPS and outer membrane porins. Inner tubes is released and the tip proteins degrade peptidoglycan and then it can insert nucleic acids
Can viruses be classified by 16S rRNA?
nope, they don’t have it
How can viruses be grouped?
host, nucleic acid composition, and envelope structure
what are poxviruses labeled as?
complex bc the intricacy of their envelope
What are the 5 steps of the viral life cycle?
1) attachment
2) entry
3) uncoating
4) viral gene expression and replication
5) assembly and release
What is adsorption? why does it require (2)?
when virus stick, requires specific ionic and pH conditions
What is tethering?
viral surface ligands can bind specifically and tightly to receptors on host cell
What is trophism?
affinity for attachment to a specific tissue
How do viruses enter?
enveloped = fuse with host cell membrane or endocytosis
non-enveloped = directly penetrate cell membrane or endocytosis
What is uncoating?
once virus is in host cell it loses their capsid
When do phages uncoat?
while entering the host cell
What is replication?
making more DNA from DNA
What is transcription?
making RNA from DNA
What is translation?
making protein from mRNA
How do viruses defy the central dogma?
replicating RNA and making DNA —-reverse transcription
What type of sense mRNA do all viruses make?
+sense mRNA
How do DNA viruses generate mRNA?
ddDNA: genomes transcribed by host RNA polymerase
ssDNA: host DNA polymerase produces missing strand
How do RNA viruses generate mRNA? what enzyme does it require?
+strand of dsRNA and some +strand ssRNA directly translate, requires RNA replicase
What do -strand RNA viruses have to carry?
preformed RNA replicase to make +RNA
How do retroviruses work?
integrate into the host genome (lysogeny)
How does HIV work?
prepackaged reverse transcriptase converts viral =RNA to DNA
How does dsDNA integrate?
integrase which is carried within the virion
How can viruses be release?
exocytosis = no cellular damage
lysis = cell bursts
How can you measure viral growth in the lab?
plaque assay
How does a plaque assay work?
1) mix culture of sensitive bacteria with phage
2) plate mixture on agar plate
3) after few hrs clear spots will appear
4) clearings (plaques) show where bacteria lysed by phage
5) count number of plaques (pfu) to find initial number of virions
