Virology 1 & 2 Lecture - Ryan

Question 1

Can viruses generate their own energy?

Answer 1

no, they must use what host cells produce

Question 2

Compare the size of viruses to bacteria?

Answer 2

viruses are much smaller. the smallest bacteria are just barely of a comparable size to the largest viruses

Question 3

What is a viroid?

Answer 3

infectious nucleic acid but has no protein component. Fairly limited to plants.

Question 4

What is a prion?

Answer 4

infectious proteins with no nucleic acids with them

Question 5

What type of RNA is the same sense as the messenger RNA?

Answer 5

+RNA

Question 6

What type of virus can have segmented genomes (chromosome like)?

Answer 6

only RNA viruses. DNA viruses are always one unit, either single or double stranded

Question 7

Which type of polymerases have proof-reading function?

Answer 7

only DNA polymerases. RNA polymerases do not and tend to make a lot of mistakes. This limits the size of RNA viruses

Question 8

What is concerted assembly?

Answer 8

as the nucleic acid is assembled, capsid proteins self-assemble around it at the same time. Common for helical structures

Question 9

What is sequential assembly headful packaging?

Answer 9

capsid structure is assembled independently from genome replication. Common for icosohedrals

Question 10

Why do viruses use repeating subunits?

Answer 10

efficiency so all the products can be encoded by the viruses small genome

Question 11

What are the consequences of virus envelopes?

Answer 11

it is a layer of protection. It changes how it enters and leaves cells.
They make viruses less stable. Always found in liquid environments

Question 12

What are the two ways viruses penetrate cells? Which one is pH dependent?

Answer 12

endocytosis - pH dependent

plasma membrane fusion - pH-independent

Question 13

What does early transcription occur immediately before?

Answer 13

genome replication

Question 14

Where do most DNA viruses replicate?

Answer 14

Nucleus

Question 15

Where do most RNA viruses replicate?

Answer 15

cytoplasm

Question 16

Virus A enters the cells by endocytosis, its naked genomes can be detected in the cytoplasm of infected cells, and virus A causes diarrhea. what can you tell about the structure?

Answer 16

non-enveloped RNA that is likely icosohedral because there are “naked genomes in the cytoplasm” suggesting sequential replication

Question 17

Why do RNA viruses have to make their own RNA polymerase molecules?

Answer 17

Human host cells only have DNA polymerases, not RNA polymerases that would work for replication.

Question 18

What is the key difference in packaging between +RNA and -RNA viruses?

Answer 18

-RNA viruses MUST package an RNA-dependent RNA polymerase with the -RNA otherwise it won’t be able to infect other cells.

Question 19

What type of DNA will retroviruses produce: single or double stranded?

Answer 19

double stranded. This allows them to use host RNA polymerase II for transcribing viral genes

Question 20

Which is more infectious: a virus with a high or low particle-pfu ratio?

Answer 20

lower particle-pfu ratios mean there are more infectious virions per physical particle so lower ratios are more infectious

Question 21

What is complementation? Which type of viruses can this happen in?

Answer 21

sharing of viral proteins.

Happens in high frequency for both RNA and DNA viruses

Question 22

You are provided a test tube mixed with two isolates of RNA virus and you are told the total titer. When you infect cells at an MOI of 0.1, no lysate is obtained. When you infect cells at n MOI of 10, a lysate is obtained. How can this be explained?

Answer 22

Most likely complementation. Could also be recombination but complementation is much more common.

Question 23

What is a syncitium?

Answer 23

multinucleated cell formed from merging of a virally infected cell with a previously non-infected cell

Question 24

What does PKR pathway respond to?

Answer 24

double stranded RNA