Viral Infectious Cycle Flashcards
what is a virion?
fully infectious viral agent (obligate intracellular)
What is the steps of viral infectious cycle?
- attachment to host cell receptor
- endocytosis to enter host cell
- lose external packaging shell of protection
- expose viral nucleic acid
- find host ribosomal machinery to make more of virion that entered
- release virions made to infect other cells by exocytosis
what are the host machinergy used by virus?
- energy (mito)
- transport vehicles
- protein translation machinery
What is a susceptible cell?
host cell that has a function receptor for virus entry
What is a permissive cell?
host cells that allows viral replication and doesn’t kill virus
for a viral infection, the host must be…
susceptible AND permissive
can every virus infect every cell? ex?
no (ex. covid respiratory cells are susceptible and permissive)
What is a resistant cell?
no receptor for viral entry
Why are fertilized chicken eggs used in lab? What is an example of its use?
- composed of many cell types that are ideal hosts for virus bc a lot of SUSCEPTIBLE AND PERMISSIVE cells
- can be used to replicate influenza virus to make flu vaccine by attenuating and injecting influenza
What are some examples of Lab hosts utilized to study infectious cycle?
- fertilized chicken eggs
- viral replication in cell culture
- whole animal hosts (non-human primates and mice)
process of making cell culture?
take human cells and grow them in growth medium at liquid food for cells
use light microscopy to see what virus does to human cells
What are ways to tell what viruses are doing to cells?
- cytopathic effects
- measure infectivity
What are Cytopathic effects?
the different changes that a virus induces inside a cell
how could you determine a viral infection under a light microscope?
dark spots + no nuclei + no cells adhering to each other (necrotic, dying cells)
Specific examples of CPEs include:
- Cell lysis: burst cells
- Syncytia: fusion of adjacent plasma cell membranes = multinucleated array of cells
- Transformation: cells are no longer flat but divide uncontrollably = round cell pile
what are the two forms of measurements for virology?
- physical measurements
- infectivity measurements
how can you Measure infectivity?
Plaque Assay with double agar method
how does a plaque assay work?
- Agar plate dyed with crystal violet with many susceptible and permissive cells (bacteria)
- you can see dark areas on plate where infection has occurred = plaques
- In these areas, bacteria are replicating virus
why do we use serial dilution or double agar method?
if bacteriophage left with bacteria on agar plate, one large plaque will form bc virus will take over
serial dilution gives single plaques
second round of agar gel (before virions leave host bacteria stops virions from leaving so you can see a single round of infection)
how can you determine degree of infectivity with plaque assay?
Count # of plaques to establish plaque forming units (pfu) /ml
what is the concept of particle to PFU ratio? how is it interpreted?
number of virus particles / number of infectious virus particles
lower ratio = more infectious
ex. 200 viral particles / 1 infectious virus particle = very high ratio = less infectious
why aren’t all viruses infectious?
host immune response
what is a Transformation assay? How is it measured?
- measure of infectivity
- certain viruses don’t form plaques but do form foci piles of infected cells
- count foci and get** foci forming units/mL**
What is an example of a virus that forms foci?
Rous Sarcoma Virus forms foci
do all viruses form plaques/foci?
no! need other measurement form - PHYSICIAL
What is a Hemaglutination assay?
Hemaglutin is a viral protein that helps viruses enter and attach to susceptible cells
- when hemaglutin interact and bind to RBC = visual cue = crystal lattice that coats tube
purpose of physical measurements?
yes or no is virus present
what is the viral enzymatic activity physical measurement? example?
measure activity of something virus has but not in host (ex. retrovirus has reverse transcriptase)
what is the immunostaining physical measurement?
tag antibodies to fluorescence, antibodies recognize viral protein = viral protein labeled = determine virus presence
what is the immunoblotting physical measurement?
extract cell contents and use electrophoresis
use labelled antibodies to detect viral protein as bands
what is the sequencing physical measurement?
amplfy sample of genome sequence to know what the genome is (identify if human or viral)
what is the** fluorescent protein** physical measurement?
- fluorescent proitens (not antibodies)
- engineer viral genomes to introduce sequences that express green fluorescent protein so that everytime a viral protein is expressed, we can see it
