Viruses 2

Question 1

importance of viruses of prokaryotes

Answer 1

they can be used to kill bacteria - bacteriophages

Question 2

genome of viruses of prokaryotes

Answer 2

majority are double stranded

Question 3

how do we detect viruses

Answer 3

biochemical (enzymatic assays and PCR and NA hybridization), serological (IF, IP, IB, ELISA, RIA), electron microscopy

Question 4

do you detect viruses and virions the same way

Answer 4

no

Question 5

how do you estimate how well virion are doing

Answer 5

if it makes 1% of what it is supposed to make - quantity over quality

Question 6

what are plaque assays based on

Answer 6

based on CPEs (growth lacking where they grow)

used in bacterial cells to demonstrate viable phage numbers, used to detect total virions in mammalian cells, viral particles must be viable

point here is that it is only used to detect virions which are viable viruses

Question 7

how are viruses used as tools?

Answer 7

• Molecular and cellular biology
– Manipulate systems to investigate function of cells
• Genetics
– Have contributed to understanding of DNA replication, transcription, translation, transport
• Gene therapy
• Immunology
– Understanding our immune system

Question 8

do viruses have protein synthesis machinery and division by binary fission

Answer 8

no – they use host’s machinery system

Question 9

where does protein synthesis for virus occur

Answer 9

in the cytoplasm of the host cell

Question 10

what are virioids and where are they usually found

Answer 10

infectious, subviral particles

found in plant diseases

Question 11

type of genome in viroids

Answer 11

small circular single stranded DNA

Question 12

do viroids encode protein

Answer 12

no but they replicate autonomously

Question 13

what are pseudovirons

Answer 13

they contain non viral DNA but are infectious and do not replicate

Question 14

what are defective virus/satellites

Answer 14

they are viral kind of viruses that cannot encode capsid protein so they depend on helper viruses for their propagation(replicating), ssRNA, and DNA

Question 15

example of a defective virus

Answer 15

Hep D

Question 16

what does Hep D (delta agent) use as its helper

Answer 16

Hep B

Question 17

why is Hep D considered “viroid-like”

Answer 17

because it does code for its own protein

Question 18

are prions viruses

Answer 18

no

Question 19

properties of prions

Answer 19

proteinaceous and infectious but no NA

Question 20

where do virophages grow

Answer 20

only in a strain of the mimivirus within the infected amoeba – that can infect us

Question 21

what is the first virophage discovered and describe it

Answer 21

sputnik: an 18 Kb circular double-stranded DNA, icosahedral virus

Question 22

what do virus need to do to propagate (to replicate)

Answer 22

– Infect an appropriate host cell
– Use the host cell to generate more of itself
– Get out of the host cell to do it all over again

Question 23

what are the phases of viral life cycle

Answer 23

• Eclipse phase - infectious virus cannot be seen or recovered from infected cells
• Maturation (there is a lot of it)
• Latent phase - progeny virus accumulates intracellularly but it hasn’t been released yet - ends when free virus is released

Question 24

when does latent period end

Answer 24

when it becomes extracellular aka when the free virus is released

Question 25

what are the five main stages of virus life

Answer 25

1) attachment (adsorption)
2) penetration (injection)
3) protein and nucleic acid synthesis
4) assembly and packaging
5) virion release

Question 26

in the influenza virus, where does transcription and replication occur

Answer 26

nucleus

Question 27

how does influenza virus get its envelope

Answer 27

by budding out of the cell after its assembly

Question 28

what type of mechanism occurs in adsorption/attachment stage of virus life cycle

Answer 28

specific and non specific

Question 29

what is the difference between susceptibility and permissibility

Answer 29

susceptibility - does the cell have the receptor required for the VAP (viral attachment protein) to attach so that the virus can get into the cell

permissibility - does the cell have the machinery needed for the virus to be able to replicate

Question 30

what determine susceptibility and what are these structures made of

Answer 30

receptors - made of protein, carb, or lipid

Question 31

what determines host range

Answer 31

interaction

Question 32

is there just one way for a virus to enter the cell

Answer 32

no there are multiple portals of entry

Question 33

how do enveloped viruses penetrate into the cell

Answer 33

• Endocytosis -> 􏰀fusion with cellular vacuoles
• Fusion of viral membrane with cellular plasma membrane (fusion mediated by specific viral protein)
• Other mechanisms

Question 34

how do non enveloped viruses penetrate into the cell

Answer 34

• adsorptive endocytosis

* other ill-defined pathways

Question 35

what does it mean for the virus to uncoat once it enters the cell

Answer 35

releases viral genome for functional expression

Question 36

is a cell susceptible and/or permissible once it gets to the protein and nucleic acid synthesis

Answer 36

• cell is susceptible because virus was able to get into it

- if cell has the ability to make protein and nucleic acid for the virus then it is permissible

Question 37

what happens in the protein and nucleic acid synthesis stage of viral life cycle

Answer 37

the virus uncoats so it takes off its capsid to expose the nucleic acid so that it can replicate and then enters the eclipse phase

Question 38

can the infectious particle be recovered once the virus has entered the protein and nucleic acid synthesis phase

Answer 38

no

Question 39

what happens in the assembly and packaging step of viral life cycle

Answer 39

new viral particles are assembled with the preformed viral particles (in cytoplasm or nucleus)

then in enveloped viruses: viral proteins associate w/ cellular membranes, aggregate in patches –> organize –> 􏰀bud from cell

Question 40

can maturation occur after initial assembly

Answer 40

yes – they can even occur after virion are released

Question 41

when does capsid assembly and encapsidation occur

Answer 41

late steps of replication cycle

Question 42

what are way in which viruses can be released

Answer 42

budding, cell lysis, poke cells in cell membrane

Question 43

difference between structural and non structural

Answer 43

structural - all proteins in mature virus particle

non structural - viral proteins in cell but not packaged

Question 44

how can one cultivate virus seeing that they cannot be grown on an agar plate

Answer 44

– susceptible organisms
– cell culture (10 and transformed cells)
– embryonated chicken eggs
– organotypic raft cultures (growing skin in an incubator)