17 - Virology

Question 1

Viruses are the smallest _______________

Answer 1

self-replicating organisms

Question 2

They have no ___________, they are obligated to invade cells and hijack the cellular machinery

Answer 2

independent metabolism

Question 3

Viruses can consist solely of a small segment of ________________ encased in a simple _____________

Answer 3

nucleic acid

protein shell

Question 4

T or F: There is an ongoing debate if viruses constitute life or not

Answer 4

T

Question 5

Positive-sense viral RNA is similar to _____ and can immediately be _______ by the host cell

Answer 5

mRNA

translated

Question 6

T or F: Purified RNA of a positive-sense virus can directly cause infection, although, it may be less infectious than the whole virus particle

Answer 6

T

Question 7

Negative-sense viral RNA is complementary to the _______ and thus must be converted to ____________ by a RNA ___________ before translation.
Purified RNA is not infectious by itself

Answer 7

mRNA
positive-sense RNA
polymerase

Question 8

Viruses containing ambisense single-stranded RNA genomes are grouped under ________________________
Ambisense means that the virus resembles a __________ sense RNA virus, however they can also translate genes from the _______ strand

Answer 8

negative sense single-stranded RNA viruses

negative

positive

Question 9

Give the characteristics (3) of enveloped viruses:

Answer 9

• have lipid-bilayer membranes
• impermeable barrier between their genomes and the outside environment
• ex: HIV, influenza

Question 10

Give the characteristics (3) of non-enveloped viruses:

Answer 10

• no membranes
• no barrier, therefore require a tightly packed protein shell to exclude nucleases or other sources of genetic damage
• ex: poliovirus / papillomavirus

Question 11

The virus binds to the surface of receptive host cells and entry is initiated by: (3)

Answer 11

• inducing conformational changes in the virus that lead to association with other receptors, membrane fusion, and penetration
• transmit signals through the membrane prepares the cell for invasion
• induction of the endocytic pathway

Question 12

T or F: viruses can only infect cells to which they can bind

Answer 12

T

Question 13

The virus triggers the penetration process and enters the __________

Answer 13

cytosol

Question 14

DNA viruses are transported to the nucleus for genome __________ or __________

Answer 14

uncoating or replication

Question 15

T or F: Several viruses have developed mechanisms to allow them to deliver their DNA to the nucleus?

Answer 15

T

Question 16

RNA viruses may be translated in the_______

Answer 16

cytosol

Question 17

Viruses rely on functions provided by their _______

Answer 17

host cells

Question 18

Almost all viruses encode and express unique ________ including ________

Answer 18

proteins

enzymes

Question 19

RNA viruses must replicate their genomes one of 2 unique ways:

Answer 19

1) RNA-dependent-RNA synthesis (RNA replication)

2) RNA-dependent-DNA synthesis (reverse transcription) followed by DNA replication and transcription (ex: retroviruses)

Question 20

All viruses must eventually express their genes as _______________ early in infection to make essential viral ___________

Answer 20

functional mRNA

proteins

Question 21

mRNA is always defined as _____________ and its complement is negative-sense

Answer 21

positive sense RNA

Question 22

Each type of virus will have different strategies to make mRNA dependent upon their starting ___________

Answer 22

genetic material

Question 23

Each of the viral replication pathways will require different enzymes : if it is an enzyme that the host encodes the virus will use the ___________ enzyme. If it is an enzyme that is not included in the host biology the virus must _______________

Answer 23

host encoded

encode its own enzyme

Question 24

What is the issue with the polymerases that catalyze RNA replication and reverse transcription?

Answer 24

-They have minimal proofreading activities

Question 25

Name the 4 important foodborne viruses:

Answer 25

1- Poliovirus 2- Hepatitis A virus 3- Norovirus 4- Rotaviruses

Question 26

RNA-dependent RNA polymerases (RdRp’s) and reverse transcriptases have an error rate that is _____ orders of magnitude higher than DNA-dependent DNA polymerases

Answer 26

three

Question 27

RNA viruses evolve at a much faster rate than their ____

Answer 27

host | *this means that the viruses sometimes can escape from host produced neutralizing antibody

Question 28

____________ are transported to a point in the host cell where they can be assembled into a viral particle

Answer 28

Macromolecules

Question 29

Most viruses rely on the ____________ for biosynthesis of their macromolecules as well as for intracellular sorting and delivery of macromolecules to the site of virion assembly

Answer 29

eukaryotic cell

Question 30

Because the same sorting mechanisms that the cell uses for it’s own molecules is used the viral macromolecules must also possess similar ___________

Answer 30

targeting signals

Question 31

Explain the main steps in virus assembly:

Answer 31

- proteins must be transported to the plasma membrane must travel through the secretory pathway of the cell - they associate with the endoplasmic reticulum and are translocated across via a proteinaceous pore - these proteins can then be transported to the golgi complex and onto to the plasma membrane unless they contain AA motifs that localize them to another location

Question 32

Intracellular transport occurs in ______________

Answer 32

coated vesicles

Question 33

Non-enveloped viruses can assemble in the ________ or the ___________

Answer 33

cytoplasm | nucleus

Question 34

For non-enveloped viruses structural proteins must be retained at the _________________ where assembly occurs

Answer 34

subcellular domain

Question 35

Enveloped viruses must acquire a ______________ from a host cell membrane during assembly

Answer 35

lipid bilayer

Question 36

Explain the virus assembly for a non-enveloped virus:

Answer 36

1- macromolecules assemble into empty capsids 2- viral DNA is inserted into the structure via a packaging sequence at one end of the genome 3- precursor core proteins are also packaged into the empty capsid along with DNA 4- proteolytic cleavage of the precursor proteins by proteinase yields the mature (infectious) virion

Question 37

What are the 3 pathways of enveloped virus assembly ?

Answer 37

1- proteins are transported to plasma membrane and assembly of the capsid and envelopment occurs simultaneously 2- capsid assembly occurs in the cytoplasm and then the virus buds from the plasma membrane and gets its envelope 3- capsid assembly occurs in the cytoplasm and gets its envelope from the ER and is exported via exocytosis

Question 38

Glycoproteins are transported to the preferred lipid bilayer of whichever virus is involved: (2)

Answer 38

- plasma membrane | - endoplasmic reticulum

Question 39

Viral capsid develops elsewhere in the cell, nucleic acids are packaged in the capsid and transported, in ______________, to the area where the envelop will be acquired

Answer 39

endosomal vesicles

Question 40

In the case of the ER the enveloped virion is transported to the plasma membrane via the ______________

Answer 40

transport vesicle

Question 41

T or F: enteric viruses are an important cause of foodborne illness in Canada and other countries

Answer 41

T

Question 42

Foodborne enteric viruses are hard to ___________ and hard to recover from contaminated foods (most are not __________)

Answer 42

detect | culturable

Question 43

What happens to foodborne enteric viruses in food systems?

Answer 43

they do not multiply in food systems, some die off rapidly during food storage and preservation

Question 44

Are foodborne enteric viruses excreted in high numbers in human feces?

Answer 44

yes

Question 45

What can kill enteric viruses:

Answer 45

- pasteurization - heat - irradiation

Question 46

T or F: foodborne enteric viruses can multiply outside the human body

Answer 46

F, they require human cells to multiply