2. How viruses replicate and change

Question 1

what are the steps in viral replication

Answer 1

attachment
entry
uncoating
viral protein synthesis
replicating the viral genome
assembly
egress from cell-budding

Question 2

what is HIV’s primary receptor and its two secondary receptors

Answer 2

primary: CD4
secondary: CCR5 and CXCR4

Question 3

what does influenza use as its receptor

Answer 3

sialic acid

Question 4

what determines what kind of cell a virus can infect

Answer 4

whether or not a cell has a specific viral receptor

Question 5

what are the two modes of entry for an enveloped virus into a cell

Answer 5

• entry at the cell membrane
• receptor mediated endocytosis

Question 6

does a lower or higher pH of the endosome help the virus enter the cytoplasm

Answer 6

endosome has a low pH which helps the virus

Question 7

define tropism

Answer 7

what kind of cell the virus can infect

Question 8

what are the two modes of entry for a naked virus into a cell

Answer 8

• endocytosis
• viropore in the plasma membrane

Question 9

define uncoating

Answer 9

release of genetic material from the virus

Question 10

what are steps in replication for DNA viruses

Answer 10

Herpesvirus example:
1. DNA into nucleus
2. Host RNA polymerase II transcribes early genes-transcription factors
3. second wave genes - transcription factors and viral DNA polymerase
4. Viral DNA replication
5. late gene production - structural proteins made
6. viral assembly in the nucleus/progeny virus

Question 11

which DNA viruses do not have a viral DNA polymerase

Answer 11

papilloma
polyoma
parvo

Question 12

DNA virus with no DNA pol. uses what to replicate their viral DNA

Answer 12

cellular DNA pol. cell needs to be in the S-phase of the cell cycle for the virus to replicate

Question 13

papilloma and polyoma can cause ______ by inhibiting ________

Answer 13

cause cell-cycle dysregulation by inhibiting pRb and making the cell go into cycle.
this can cause the cell to become cancerous if it does not die

Question 14

parvo cannot cause the cell to enter ______ and must infect cells ______

Answer 14

S-phase
already replicating

Question 15

where does the DNA replication normally occur

Answer 15

nucleus

Question 16

how is poxviruses an exception to DNA viruses

Answer 16

replicate in the cytoplasm, not the nucleus. they have a viral DNA-dependent RNA pol. used to make mRNA

Question 17

how is the hepadnavirus (HBV) an exception to DNA viruses

Answer 17

has a reverse transcriptase. replicated in both the nucleus and cytoplasm

Question 18

+ssRNA is the same as ____

Answer 18

mRNA

Question 19

what is the first thing that +ssRNA viruses do when they enter the cell

Answer 19

use cellular machinery to translate their +ssRNA into a large polyprotein

Question 20

which 4 DNA viruses use their own viral polymerases to make more genetic material

Answer 20

adeno
herpes
pox
hepadna

Question 21

which viruses are the exception to +ssRNA viruses

Answer 21

retroviruses
- makes dsDNA from its +ssRNA with a viral reverse transcriptase
- this dsDNA gets integrated into the nucleus and is there for the life of the cell
- cell then makes mRNA

Question 22

what do all +ssRNA viruses contain

Answer 22

a viral protease
- they need to celave this polyprotein to make individual viral proteins

Question 23

what do all +ssRNA viruses need to make

Answer 23

a viral RNA-dependent RNA polymerase
- need to make more RNA from their own RNA
- cell does not have any RNA-dependent RNA pol. so need to make one

Question 24

what are good targets for +ssRNA viruses

Answer 24

viral protease and viral polymerase

Question 25

what happens once a retrovirus makes a DNA copy of their genetic material

Answer 25

they integrate the copy into the host cell chromosome. that viral DNA copy is in the cel for the life of the cell

Question 26

-ssRNA viruses are all _____ and ______

Answer 26

helical and enveloped

Question 27

what is the first thing that -ssRNA viruses do when they enter the cell and how do they do it

Answer 27

make mRNA from their -ssRNA.
- they do this using a viral pol. that they carry into the cell with them in their virion

Question 28

do -ssRNA viruses need a viral protease

Answer 28

no they do not need a viral protease because they make mRNA for each viral protein

Question 29

-ssRNA do require a _______ _______

Answer 29

viral pol. that they bring into the cell in their virion

Question 30

hepatitis D virus is a ______ virus that must ________

Answer 30

defective
co-infect a cell with HBV to replicate

Question 31

what is required for gene reassortment and which viruses have this requirement

Answer 31

segmented genome
BOAR virus
- bunya
- orthomyxo
- arena
- reo

Question 32

define gene reassortment

Answer 32

when two strains of the same segmented virus infect the same cell. the resulting viruses have segments from both infecting strains resulting in a very different virus from the parental strains

Question 33

what is responsible for the majority of influenza pandemics

Answer 33

gene reassortment

Question 34

does antigenic drift or shift lead to small changes

Answer 34

antigenic drift

Question 35

which organisms have the highest rate of mutation

Answer 35

higher eukaryotes < prokaryotes < DNA viruses < RNA viruses

Question 36

define viral quasi-species

Answer 36

if you have a chronic infection, which allows the virus to replicate many times, you could have lots of different viruses in the body at any one time (HIV and HCV) or put another way, many quasi-species of the virus