Viral Infectious Cycle

Question 1

what is a virion?

Answer 1

fully infectious viral agent (obligate intracellular)

Question 2

What is the steps of viral infectious cycle?

Answer 2

1. attachment to host cell receptor
2. endocytosis to enter host cell
3. lose external packaging shell of protection
4. expose viral nucleic acid
5. find host ribosomal machinery to make more of virion that entered
6. release virions made to infect other cells by exocytosis

Question 3

what are the host machinergy used by virus?

Answer 3

1. energy (mito)
2. transport vehicles
3. protein translation machinery

Question 4

What is a susceptible cell?

Answer 4

host cell that has a function receptor for virus entry

Question 5

What is a permissive cell?

Answer 5

host cells that allows viral replication and doesn’t kill virus

Question 6

for a viral infection, the host must be…

Answer 6

susceptible AND permissive

Question 7

can every virus infect every cell? ex?

Answer 7

no (ex. covid respiratory cells are susceptible and permissive)

Question 8

What is a resistant cell?

Answer 8

no receptor for viral entry

Question 9

Why are fertilized chicken eggs used in lab? What is an example of its use?

Answer 9

• 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

Question 10

What are some examples of Lab hosts utilized to study infectious cycle?

Answer 10

1. fertilized chicken eggs
2. viral replication in cell culture
3. whole animal hosts (non-human primates and mice)

Question 11

process of making cell culture?

Answer 11

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

Question 12

What are ways to tell what viruses are doing to cells?

Answer 12

1. cytopathic effects
2. measure infectivity

Question 13

What are Cytopathic effects?

Answer 13

the different changes that a virus induces inside a cell

Question 14

how could you determine a viral infection under a light microscope?

Answer 14

dark spots + no nuclei + no cells adhering to each other (necrotic, dying cells)

Question 15

Specific examples of CPEs include:

Answer 15

• 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

Question 16

what are the two forms of measurements for virology?

Answer 16

1. physical measurements
2. infectivity measurements

Question 17

how can you Measure infectivity?

Answer 17

Plaque Assay with double agar method

Question 18

how does a plaque assay work?

Answer 18

• 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

Question 19

why do we use serial dilution or double agar method?

Answer 19

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)

Question 20

how can you determine degree of infectivity with plaque assay?

Answer 20

Count # of plaques to establish plaque forming units (pfu) /ml

Question 21

what is the concept of particle to PFU ratio? how is it interpreted?

Answer 21

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

Question 22

why aren’t all viruses infectious?

Answer 22

host immune response

Question 23

what is a Transformation assay? How is it measured?

Answer 23

• 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**

Question 24

What is an example of a virus that forms foci?

Answer 24

Rous Sarcoma Virus forms foci

Question 25

do all viruses form plaques/foci?

Answer 25

no! need other measurement form - PHYSICIAL

Question 26

What is a Hemaglutination assay?

Answer 26

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

Question 27

purpose of physical measurements?

Answer 27

yes or no is virus present

Question 28

what is the viral enzymatic activity physical measurement? example?

Answer 28

measure activity of something virus has but not in host (ex. retrovirus has reverse transcriptase)

Question 29

what is the immunostaining physical measurement?

Answer 29

tag antibodies to fluorescence, antibodies recognize viral protein = viral protein labeled = determine virus presence

Question 30

what is the immunoblotting physical measurement?

Answer 30

extract cell contents and use electrophoresis

use labelled antibodies to detect viral protein as bands

Question 31

what is the sequencing physical measurement?

Answer 31

amplfy sample of genome sequence to know what the genome is (identify if human or viral)

Question 32

what is the** fluorescent protein** physical measurement?

Answer 32

• 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