Virology: Chapter 2

Question 1

Explain the process of adsorption and attachment

Answer 1

Adsorption = initial contact
so the virus bumps into the host cell via random collisions, doesn’t need energy

Attachment = specific binding
protein on the surface binds to the virus receptor

Question 2

Host range

Answer 2

Are what cells the virus can infect
cells = that have receptors!
determined by
- receptor in the cells
- intracellular factors needed to replicate

Question 3

Narrow Host Range

Answer 3

Very specific
HIV: CD4 protein which are specific immune cells

Question 4

Wide Host Range

Answer 4

Very broad
Measles: CD60 protein which are found most human cells

Question 5

Susceptible

Answer 5

cell has the receptor = virus can bind and enter their genome

Question 6

Permissible

Answer 6

cell has the correct machinery for the viral genome to replicate and produce progeny virus

Question 7

How can we prevent viruses from attaching to the cells

Answer 7

Vaccines
- induce the production of neutralizing antibodies that bind to the anti-receptors so the virus can’t bind

Block Host Cell Receptor
- use antibodies to block virus receptor
e.g SARS COV 19 = ACE-2 receptors

Question 8

What is the disadvantage of blocking ACE-2 receptors?

Answer 8

that receptor is important for cell functions like regulating blood pressure, so if you block it (so covid cannot bind), there will be side effects

Question 9

Is Genome Entry energy dependent?

Answer 9

Yes. it uses energy

Question 10

What are the 4 ways a genome can enter a host cell?

Answer 10

1. Endocytosis + Uncoating
2. Endocytosis + Pore Formation
3. Endocytosis + Membrane Fusion (ENVELOPE only)
4. Direct Membrane Fusion (ENVELOPE only)

Question 11

Endocytosis + Uncoating

Answer 11

virus binds, form endosome, endosome take virus into the cell, capsid breaks, genome enters cytoplasm

Question 12

Endocytosis + Pore Formation

Answer 12

virus binds, endosome takes virus into the cell. virus forms a pore in endosome membrane, genome pass through pore

Question 13

Endocytosis + Membrane Fusion (ENVELOPED ONLY)

Answer 13

virus binds, endosome takes it into the cells, virus ENVELOPE fuses with endosome membrane, genome released

Question 14

Direct Membrane Fusion (ENVELOPED ONLY)

Answer 14

virus binds and directly fuses with the host cell’s plasma membrane, genome enters

Question 15

Genome Replication and Expression has 2 functions, which are

Answer 15

• genome used as a template to make more genome copies, more progeny virus
• genome used to make viral mRNA to make viral protein

Question 16

What are some limitations that a host cell presents to a virus with regards to its replication (2)

Answer 16

• not the right virus receptor = can’t attach
• not the right enzymes / host factors = virus can’t replicate

Question 17

Can a cell be susceptible but not permissive? Can a cell be resistant to a viral infection, yet be permissive to viral infection?

Answer 17

YES

Question 18

Do viruses make their own amino acids and nucleotides during replication?

Answer 18

NO, its NOT independent

Question 19

Do viruses use their host cell’s ribosomes?

Answer 19

YES

Question 20

What does host cell RNA Pol. do?

Answer 20

read DNA template from 3’ to 5’, and synthesize from 5’ to 3’

Question 21

Ribosome translate (+) mRNA from

Answer 21

5’ to 3’

Question 22

All virus genomes are surrounded by proteins called…

Answer 22

capsids

Question 23

function of the capsid

Answer 23

PROTECT AND DELIVER
protect the genome from:
- nucleases in environment
- damaging agents
- mechanical force

deliver virus genome to the location of replication and expression in the host cell

Question 24

why does the capsid must be stable enough yet unstable enough

Answer 24

stable enough to protect, unstable enough to be broken down so genome can be released

Question 25

What type of interactions exist between proteins and subunits of the capsid

Answer 25

protein-protein interactions that cause conformational change to the capsid so genome can be released

Question 26

What might cause capsid to change from a stable to unstable structure

Answer 26

cut, pH, heat

Question 27

Explain the relation between DNA virus and the cell cycle replication in regards to permissiveness

Answer 27

if cell cycle is in G1, the DNA is still growing, so the host cell is not permissive if cell cycle is in S, the DNA is synthesized, so the host cell is permissive

Question 28

Explain why RBC are never permissive

Answer 28

because they lack a nucleus, so they cannot make amino acids, virus can't replicate

Question 29

Explain why mouse cells are permissive, but NOT susceptible to Polio, making them NOT resistant

Answer 29

because you can inject polio (RNA virus) to the cytoplasm and the virus can replicate, but the mouse cell doesn't have the right receptors for the virus to bind and enter naturally

Question 30

Why do naked viruses survive longer in the environment? and are more virulent?

Answer 30

Because they just have a protein capsid, and they cause cell lysis (so host cell die)

Question 31

Why are enveloped viruses more fragile and sensitive, and less virulent?

Answer 31

Because they're lipid bilayer is fragile and sensitive to pH and heat, so they break easily, making the virus less stable, and less virulent and they don't always cause cell lysis, they sometimes bud.

Question 32

Why some viruses package their own replicative enzymes in their capsid?

Answer 32

Because some viruses replicate in the cytoplasm so they cannot access the host cells DNA/RNA Polymerase because they're in the nucleus

Question 33

Why do RNA viruses use RDRP (like they encode they're own enzyme no matter the location)

Answer 33

because host cell RNA Pol doesn't read RNA template, they read DNA template

Question 34

RNA and DNA virus can replicate in...

Answer 34

cytoplasm or nucleus

Question 35

if DNA virus replicates in the nucleus, then they use DNA / RNA Pol of the

Answer 35

host cell

Question 36

if DNA virus replicate in the cytoplasm, then the virus genome use DNA / RNA pol of the..

Answer 36

virus itself (code by itself) so the capsid contains pre-made pol

Question 37

RNA viruses encode what enzyme

Answer 37

RDRP

Question 38

RNA viruses only have pre-made RNA pol IN THEIR CAPSID only if...

Answer 38

RNA is (-) stranded

Question 39

If the RNA (+) strand (RNA virus) then

Answer 39

the virus will make RNA pol AFTER infecting the cell, not pre-made

Question 40

Retrovirus pathway of genome replication and expression

Answer 40

RNA --> ss RNA --> ds DNA ---> ss RNA

Question 41

what enzyme retrovirus uses to transcribe ssRNA to dsDNA

Answer 41

RT

Question 42

Advantages of a retrovirus

Answer 42

use cell's RNA Pol and integrate into the cell genome making it hella dangerous

Question 43

if viral mRNA doesn't have a 5'cap, it uses

Answer 43

a secondary structure

Question 44

viral mRNA can be monocistronic and polycistronic, why are polycistronic viral mRNA's not good at translation

Answer 44

because the ribosomes would read one gene and then stop

Question 45

so what's the strategy to overcome this

Answer 45

translate entire mRNA into polyprotein and then cut it up into individual proteins (capsid, rdrp, etc)

Question 46

(+) double stranded nucleic acid

Answer 46

same sequence as mRNA

Question 47

(-) double stranded nucleic acid

Answer 47

template for making (+) strand

Question 48

the (+) and (-) ds are...

Answer 48

complementary

Question 49

For ss RNA viruses (+) strand RNA...

Answer 49

has the coding sequence and can be translated directly by host ribosomes it still must be transcribed to synthesize mRNA (+) --> (-) ---> (+)

Question 50

For ss RNA viruses (-) strand RNA...

Answer 50

can't be directly translated, must be transcribed to make a complementary (+) strand that acts as mRNA