Virus Life Cycle 1

Question 2

What term refers to the interactions between viruses and specific species or tissues before binding occurs?

Answer 2

Recognition

Question 3

What term refers to the entry of a virus particle (virion) into a cell?

Answer 3

Penetration

Question 4

What term refers to the binding of a viral surface molecule to its specific cellular receptor?

Answer 4

Attachment

Question 5

What term refers to the species that a virus preferentially infects?

Answer 5

Host range

Question 6

What term refers to the preferred cell type that a virus infects?

Answer 6

Tissue tropism

Question 7

What term describes a cell that can support virus replication and virion synthesis?

Answer 7

Permissive

Question 8

What term describes a cell that a virus can enter?

Answer 8

Susceptible

Question 9

Describe the attachment and penetration of rotavirus into a host cell.

Answer 9

Attachment: capsid to cell membrane (rotavirus is non-enveloped)
Penetration: endocytosis + endosome lysis

Question 10

Give the host range, recognition tissue, and tissue tropism for rotavirus.

Answer 10

Host range: humans, some mammals and birds
Recognition: GI mucosa
Tropism: enterocytes

Question 11

Describe the attachment and penetration of Epstein-Barr Virus into a host cell.

Answer 11

Attachment: envelope to ECM & cell membrane (EBV is enveloped)
Penetration: fusion of envelope to plasma membrane + uncoating at the nuclear pore

Question 12

Give the host range, recognition tissue, and tissue tropism for Epstein-Barr Virus.

Answer 12

Host range: humans only (Herpesviruses and HIV are humans-only)
Recognition: oral mucosa
Tropism: epithelial cells and B cells

Question 13

A certain naked virion attaches to a membrane receptor and forms a pore in the plasma membrane. Uncoating occurs through the pore, either at the plasma membrane or within an endosome. What virus from lecture is being described?

Answer 13

Poliovirus

Question 14

What cells are susceptible and/or permissive for HIV?

Answer 14

Only human CD4 T cells are susceptible, although all T cells would be permissive if the virus could enter. (Also macrophages can become susceptible and permissive as the virus grows and mutates)

Question 15

What term describe the release of the viral genome into a cell?

Answer 15

Uncoating

Question 16

List 3 common mechanisms for virus uncoating.

Answer 16

1. Uncoating at the plasma membrane
2. Uncoating within endosomes
3. Uncoating at the nuclear membrane

Question 17

What enzymes do RNA viruses, DNA viruses, and Retroviruses use to make mRNA?

Answer 17

RNA viruses use RDRP (RNA-dependent RNA Polymerase); DNA viruses and Retroviruses use host RNA Polymerase II

Question 18

Which strand of RNA is used to make proteins: the (+) or (-) strand? What does the other strand do?

Answer 18

The positive/sense/mRNA strand encodes for proteins. The negative strand can be used to make more (+) strands or packaged into a virion

Question 19

List up to 4 factors that contribute to the high mutation rate of RNA viruses.

Answer 19

High processivity/efficiency of RDRP, low fidelity of RDRP, high recombination rates, high reassortment of gene segments

Question 20

Describe where in a cell RDRP is usually found. How does it move during RNA transcription?

Answer 20

In the cytoplasm, but attached to a cell membrane - it stays stationary while the RNA moves through

Question 21

FIll in the blanks. In a RNA virus, RNA is both ____________ and _____________.

Answer 21

the genetic material; the mRNA / template for protein synthesis

Question 22

What molecules in an RNA virus can make proteins out of the RNA templates?

Answer 22

Host ribosomes

Question 23

Just for clarity’s sake, what exactly does RDRP do anyways? Does it: synthesize (+)RNA from (-)RNA, synthesize (-)RNA from (+)RNA, synthesize mRNA from (+)RNA, and/or synthesize proteins from mRNA?

Answer 23

Only the first 2 choices. RDRP just copies RNA, it doesn’t synthesize proteins (that’s a ribosome’s job). Also mRNA is synthesized from (-)RNA.

Question 24

Name the main RNA virus whose RDRP functions in the nucleus instead of in the cytoplasm. What molecule carries the RDRP into the nucleus?

Answer 24

Influenza; nucleoprotein (NP) carries it

Question 25

If the mutation rate of E. coli RNA polymerase is about 1 error in 10^6 nucleotides, what is the approximate error rate of RDRP?

Answer 25

About 1 in 10^3-10^4

Question 26

In what phase of the viral growth curve are no viruses recoverable because replication and assembly are happening?

Answer 26

Eclipse phase

Question 27

What term describes the number of infectious viral progeny created during a single round of replication?

Answer 27

Burst size

Question 28

In what phase of the viral growth curve are virions made and able to infect other cells?

Answer 28

Maturation and release phase

Question 29

What term, used to describe viruses as a whole, captures the idea that they are not pure populations but mixtures of mutated genomes?

Answer 29

A quasi-species