Viruses Flashcards
(37 cards)
General characteristics
-obligate intracellular paracites
-acellular
-have either DNA or RNA
have protein coat
-no ribosomes
-no ATP-generation
-no enzymes
-20-1000 nm (only seen with e microscope)
host range
the spectrum of host cells a virus can infect
- most infect specific types of cells in host
- determined by attachment cites and cellular factors
DNA viruses
single or double stranded, linear or circular
RNA viruses
linear, single or double stranded, one molecule or segmented
capsid
protein coat around nucleic acid
- made of capsomeres = 1 protein or multiple dif ones
function: carries NA from cell to cell, protects NA from nucleases, attaches to cell receptors (naked viruses), is antigenic
envelope
surrounds nucleocapsid of some animal viruses
- made of host cell lipids and viral proteins
- lipid bilayer sourounding capsid
- spikes are antigenic and aid in attachment
- can change viral proteins to avoid antibiotics
Types of viral morphology
- helical
- polyhedral
- enveloped
- complex
helical viruses
nucleic acid spirals
-many copies of the same protein wrapped in helical conformation with NA inside
polyhedral viruses
- icosahedral = 20 sides and each side is an equilateral triangle
- adenovirus
- polio
enveloped virus
-dif shapes on the inside, but apperes spherical bc of envelope
complex viruses
- capsid head w/ NA
- sheath
- base plate
- tail fiber
- pin
- e.g. phage or orthopoxvirus
taxonomy
- genus = -virus
- family = -viridae
- order = -ales
- species = common name
- sub species = a number
species = viruses that share some genetic info and ecological niche (host)
Why are viruses typically grown in bacteria in lab
bc it is the cheapest way—> bacteria need living host
-bacteriophages form plaques on lawn –> PFU
3 ways of growing animal virus in lab
- in living animal
- in embryonated eggs
- in cell cultures
growing bacteria in cell cultures
- treat tissue with enzyme that separates cells
- put cells in growth solution
- virally infected cells are detected via deterioration (cytopathic effect
continuous cell lines
normal cells grow in monolayer + adhere to glass
infected ones stack up
viral identification
- cytopathic effect
- serological testing (western blotting = reaction of virus with antibodies)
- Nucleic acids –> PCR
requirements for viral multiplication
must infect host
must override host’s metabolic machinery
one-step growth curve
- eclipse period
- virions released from host cell
- acute period
lytic life cycle
- tail fibers recognize attachment site
- virion squats down
- lysozyme on tail fiber hydrolyzes cell wall
- tail sheath contracts
- tail core goes through cell wall
- DNA is injected
- capsid stays outside
- transcription of viral DNA
- translation of viral mRNA
- no more host DNA or protein synthesis
- assembly of phage particles
- phage lysozyme breaks cell wall + releases virions
lysogenic life cycle
- starts same as lytic, but viral DNA is incorporated into host chromosome
- viral DNA = prophage
- host replicates its own chromosome with prophage
- Phage conversion = host cell exhibits new properties (only if 1 or more phage gene is expressed)
- host cell immune to re-infection by same virus
- can be responsible for specialized transduction
Steps of animal virus multiplication
- attachment
- penetration
- uncoating
- biosynthesis
- maturation
- release
attachment/absorption (animal)
- attach through receptors on host cell’s surface (proteins and glycoproteins on membrane)
- viral particles have spikes or fibers that bind
- naked viruses have attachment sites on nucleocapsid
- enveloped viruses have them on envelope
penetration / uncoating
- enveloped viruses fuse with outer membrane of host
- naked viruses’ capsids degrade on outer membrane
- Both use receptor-mediated-endocytosis
