lecture 2- viral replication

Question 1

what is a virion?

Answer 1

extracellular or intracellular infectious form of a virus

Question 2

what are the 6 basic steps of viral infection/replicaiton

Answer 2

1. viral attachment
2. endocytosis
3. uncoating
4. replication
5. assembly
6. egress

Question 3

eclipse period

Answer 3

the period between the entry of the virus genetic material into the host, causing infection and the appearance of new mature virus in a host cell

Question 4

latent period

Answer 4

before virus is released

Question 5

tissue tropism depends on … (2)

Answer 5

• susceptibility (suitable receptors on host)
• permissivity (host cellular machinery must be able to support viral replication and release)

Question 6

how do enveloped viruses enter a cell

Answer 6

virus attaches to host plasma membrane at receptor sites with glycoproteins then envelope is lost during endocytosis (uncoated) and only nucleus and capsid enters the cell

Question 7

how do naked viruses enter a cell (2 mechanisms)

Answer 7

whole virus enters in a vesicle made from host plasma membrane (ex: adenoviruses)

OR

only genome enters via pore-mediated penetration (ex: picornaviruses)

Question 8

which of the following steps is used by all viruses?

translation
transcription
RNA rep
DNA rep
reverse transcription

Answer 8

translation

Question 9

why doesnt pox virus replicate in the nucleus, despite being a DNA virus?

Answer 9

poxvirus has its own transcriptase and thus does not need to replicate in nucleus

Question 10

where do most DNA viruses replicate? why?

Answer 10

most replicate in host nucleus because they need cellular polymerase and RNA polymerase 2

Question 11

where do most RNA viruses replicate? why?

Answer 11

most RNA viruses replicate in host cytoplasm because

a) +vs sense viruses can act as mRNA

and

b) -ve sense viruses carry RNA dependent RNA polymerase

Question 12

what are the exceptions to RNA viruses replicating in cytoplasm?

Answer 12

retroviruses replicate in nucleus and cytoplasm

influenza replicates in nucleus

hepadnavirus replicates in nucleus and cytoplasm

Question 13

replication strat of dsDNA

Answer 13

host cell Pol (except pox)

Question 14

replication strat of ssDNA

Answer 14

host cell Pol –> dsDNA intermediate

Question 15

replication strat of dsRNA

Answer 15

do not depend on host Pol–> carry viral RNA pol

Question 16

replication strat of +ve ssRNA

Answer 16

directly access host ribosome

Question 17

replication strat of -ve ssRNA

Answer 17

carry viral pol (RdRp) –> +ve ssRNA intermediate

Question 18

replication strat of ssRNA (retro)

Answer 18

DNA intermediate –> integration into host genome (carry reverse transcriptase and integrase)

Question 19

true or false: herpesvirus is very highly regulated

Answer 19

true

Question 20

what differentiates the replication style of herpesvirus

Answer 20

• very highly regulated
• alpha, beta and gamma regulatory proteins (cascade, starting with alpha)
• DNA virus –> replication occurs in nucleus

Question 21

what differentiates the replication style of flavivirus?

Answer 21

• RNA viral rep (replication occurs in cytoplasm)
• less regulated
• +ve sense RNA
• creation of polyproteins
  -envelopment by plasma membrane

Question 22

what 2 enzymes are needed for retrovirus replication

Answer 22

reverse transcriptase and intergrase

Question 23

what role does intergrase have in retrovirus replication

Answer 23

integrates viral genome into host genome in host nucleus

Question 24

lysis of the host cell more commonly occurs with a) enveloped or b) naked viruses?

Answer 24

b) naked viruses

usually accumulate in nucleus or cytoplasm and release by lysis of host cells, vs enveloped which bud off of plasma membrane

Question 25

examples of enveloped viruses

Answer 25

herpes, pox

Question 26

examples of naked viruses

Answer 26

adeno, picorno, reo, calici

Question 27

what viruses replicate in both the nucleus and the cytoplasm?

Answer 27

hepadnavirus and retroviruses

Question 28

when replication occurs in the cytoplasm, what is this called?

Answer 28

reverse transcription

Question 29

are enveloped viruses infectious before their envelope is acquired?

Answer 29

no

Question 30

where can enveloped viruses be released/budded off from

Answer 30

mucosal surface
endoplasmic reticulum
cytoplasm
golgi
nucleus
basal surface

Question 31

can viruses replicate in water?

Answer 31

not without a living host

Question 32

what is special about poxvirus in regards to viral replication

Answer 32

despite being a DNA virus, it replicates in the cytoplasm

Question 33

what is special about influenza in regards to viral replication

Answer 33

despite being a RNA virus, it replicates in the nucleus