Microbio Week 9 - How Viruses Replicate and Change (Exam 3)

Question 1

Are viruses good targets for antivirals?

Answer 1

NO

Question 2

What do viruses use for replication?

Answer 2

Host cellular products

Question 3

Name the steps of replication

Answer 3

1. Attachment
2. Tropism
3. Entry

Question 4

How does a virus attach?

Answer 4

Bind to cellular receptors on host cell

Question 5

If a cell does not have the viral receptor, the virus cannot do what?

Answer 5

Infect the cell

Question 6

What helps determine what cells the virus can infect (aka the tropism of the virus)?

Answer 6

The viral receptor

Question 7

T/F: There are other determinants of tropism other than receptors. For example, some viruses can enter certain cells, but if the cells are missing a cellular factor required for viral replication, the virus will not be able to replicate

Answer 7

True

Question 8

What determines not only what cell type the virus infects but also the species of animal it can infect?

Answer 8

Tropism

Question 9

What type of transmission is tropism important in?

Answer 9

Zoonotic

Question 10

Entry at the cell membrane is mainly used for what type of viruses?

Answer 10

Enveloped

Question 11

Some enveloped viruses can fuse the lipid bilayer of the virus with what?

Answer 11

The cell membrane

Question 12

Both enveloped and naked viruses can be ___________

Answer 12

endocytosed

Question 13

What helps the virus enter the cytoplasm from the endosome?

Answer 13

Lower pH of the endosome

Question 14

Where does most DNA virus replication occur?

Answer 14

Nucleus

Question 15

Where does DNA virus replication occur for poxvirus? (exception)

Answer 15

Cytoplasm

Question 16

Where does DNA virus replication occur for HBV? (exception)

Answer 16

Nucleus + cytoplasm

Question 17

What are the 3 DNA viruses that do NOT make their own viral DNA polymerase?

Answer 17

Papillomavirus
Polyomavirus
Parvovirus

Question 18

What do Papillomavirus, Polyomavirus, and Parvovirus use to replicate their viral DNA?

Answer 18

Cellular DNA polymerase

Question 19

What phase of the cell cycle must the cells be in for Papillomavirus, Polyomavirus, and Parvovirus to replicate their viral DNA?

Answer 19

S-phase

Question 20

Papillomavirus and polyomavirus can cause cell-cycle ____________ by inhibiting pRb and making the cell go into cycle.

However, if the virus causes cell cycle dysregulation but does not kill the cell, there is a chance for the cell to become ______________

Answer 20

dysregulation; cancerous

Question 21

Which virus (papilloma, polyoma, or parvo) cannot cause the cell to enter the S-phase and must infect cells already replicating?

Answer 21

Parvovirus

Question 22

What do poxviruses have to make mRNA?

Answer 22

DNA-dependent RNA polymerase

Question 23

What does HBV have?

Answer 23

Reverse transcriptase

Question 24

mRNA is the same as what?

Answer 24

+ssRNA

Question 25

When +ssRNA viruses enter the cell, what can they do right away?

Answer 25

Make protein

Question 26

the first thing +ssRNA viruses do when they enter the cell is use the cellular machinery to translate their +ssRNA into a large polyprotein. What is the exception?

Answer 26

Retroviruses

Question 27

+ssRNA must cleave the large polyprotein they make into what individual viral __________. This means all +ssRNA viruses have what?

Answer 27

proteins; viral protease

Question 28

T/F: All RNA viruses must make a viral RNA-dependent RNA polymerase

Answer 28

True!

Question 29

What 2 things do all +ssRNA viruses have that are excellent targets for antiviral drugs?

Answer 29

Viral protease + polymerase

Question 30

Retroviruses are +ssRNA viruses with how many copies of the same genetic material?

Answer 30

2

Question 31

Which virus is diploid?

Answer 31

Retrovirus

Question 32

Why are retroviruses unique?

Answer 32

Make a DNA copy of themselves using reverse transcriptase as part of their replication cycle

Question 33

T/F: The reverse transcriptase used by retroviruses is carried into the cell; it is in the virion

Answer 33

True

Question 34

Once retroviruses make a DNA copy of their genetic material, they integrate that copy into the host cell chromosome. How long is that viral DNA copy in the cell?

Answer 34

For the life of the cell

Question 35

Retroviruses use the cellular RNA polymerase to make viral ________ from the integrated viral DNA. This mRNA travels to the ___________, where it is made into _____________

Answer 35

mRNA; cytoplasm; protein

Question 36

In HIV (a retrovirus), when does the viral protease cleave the viral proteins?

Answer 36

After budding of the virion

Question 37

What helps mature viral particles from retroviruses?

Answer 37

Protease

Question 38

What is the first thing -ssRNA viruses do when they enter the cell?

Answer 38

Make mRNA from their -ssRNA

Question 39

How do -ssRNA viruses make mRNA from their -ssRNA?

Answer 39

Use a viral polymerase that goes into the cell with them in their virion

Question 40

Do -ssRNA viruses need a protease?

Answer 40

NO - they make mRNA for each viral protein

Question 41

Which virus is a "defective" virus that must co-infect a cell with HBV in order to replicate?

Answer 41

Hep D virus

Question 42

What is this describing? 2 viruses of the same type infect the same cell. They might switch parts of their genome by recombination, which can result in several proteins being replaced at a time between the strains, resulting in a large change

Answer 42

Gene recombination

Question 43

What is needed for gene reassortment?

Answer 43

Segmented genome

Question 44

Which family of viruses have segmented genomes?

Answer 44

BOAR viruses (bunya, orthomyxo, arena, reo)

Question 45

What is it called when two strains of the same segmented virus infect the same cell?

Answer 45

Reassortment

Question 46

What is this describing? The resulting viruses have segments from both infecting stains, resulting in a very different virus from the parental strains

Answer 46

Reassortment

Question 47

What is responsible for the majority of influenza pandemics?

Answer 47

Reassortment

Question 48

2 examples of antigenic shift (large changes)

Answer 48

Recombination Reassortment

Question 49

Example of antigenic drift (small changes)

Answer 49

Mutation

Question 50

Different polymerases have different _________; they have different error rates and ability to correct mistakes

Answer 50

fidelity

Question 51

Rank the following from lowest to highest mutation rate: DNA viruses RNA viruses Higher eukaryotes Prokaryotes

Answer 51

Higher eukaryotes < Prokaryotes

Question 52

T/F: A base inserted by mistake will not be corrected by RNA viruses, leading to a higher mutation rate

Answer 52

True

Question 53

Most RNA viruses cannot do what?

Answer 53

Proofread

Question 54

T/F: It is possible in chronic infections, when antiviral therapy is started, a virus carrying a mutation resistant to the antiviral is already present. This can be true for HIV and HCV, which is why combination therapy is so necessary

Answer 54

True

Question 55

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 _______________ of the virus

Answer 55

quasi-species

Question 56

What helps viruses change rapidly with changing environmental conditions?

Answer 56

Making single nucleotide changes every 1-100 viruses produced