Virus Entry to Host Cell

Question 1

Describe the steps to a very basic and all encompassing replication strategy.

Answer 1

Enter host cell
Replicate genome
Make mRNA
Make proteins
Assemble virions
Escape from host

Question 2

What determines cell tropism?

Answer 2

Receptors which make a cell susceptible to virus entry and replication.

Question 3

What is the mechanism name of membrane fusion and fission?

Answer 3

Hairpin

Question 4

How do virions enter the cell?

Answer 4

Either by endocytosis or cell fusion.

Question 5

Which viruses use pore formation?

Answer 5

Non-enveloped viruses

Question 6

What are the steps to viral entry

Answer 6

Weak binding
Strong and specific binding to receptor
Enhanced binding
Nucleocapsid enters cytoplasm

Question 7

How can cells prevent viral entry?

Answer 7

Antibodies: via immune response or IVIG therapy
Dendrimers: nanobiotech or novel therapeutics

Question 8

Describe early viral genes/proteins.

Answer 8

Enable genome replication
Expressed at low levels
Often effect RNA or DNA synthesis machinery
Often effect cell cycle progression

Question 9

Describe late viral genes/proteins.

Answer 9

Can be made using newly replicated genomes
Abundant expression
Used to package genomes and assemble virions

Question 10

What are the outcomes of viral replication?

Answer 10

Acute, chronic, latent, or transformational infections

Question 11

What are the patterns of viral infection?

Answer 11

Acute, chronic, latent, or slow.

Question 12

What is a characteristic of the domain archaea that bacteria and eukarya do not have?

Answer 12

They are not, so far as we know, infected by viruses.

Question 13

Describe RNA dependant RNA polymerases

Answer 13

Reads RNA, makes RNA
Encoded by viruses only
No proof reading
1 mistake: 10^3-10^5 nt

Question 14

Describe DNA dependent RNA polymerase

Answer 14

Reads DNA, makes RNA
Encoded by viruses and hosts
Some proof reading
1 mistake: 10^4-10^5 nt

Question 15

Describe RNA dependent DNA polymerase

Answer 15

Reads RNA, makes DNA
Encoded only by retroviruses
No proof-reading
1 mistake: 10^4 nt

Question 16

Describe DNA dependent DNA polymerase

Answer 16

Reads DNA makes DNA
Encoded by viruses and hosts
Proof reading
1 mistake: 10^7-10^9 nt

Question 17

Name the mechanisms for virus genome variation.

Answer 17

Mutation, recombination, rearrangement, reassortment

Question 18

Describe viral mutation.

Answer 18

Point mutations
Accuracy of polymerases
Hot spots
Creates antigenic drift

Question 19

Describe viral recombination

Answer 19

Can occur during dual infections
HGT
Generation of new virus strains
Has recombination rate (e.g. HIV RR 2.8)

Question 20

Describe viral rearrangement

Answer 20

Gene reordering and/or duplication

Question 21

Describe viral reassortment

Answer 21

Occurs in viruses with fragmented genomes
Analagous to sexual repro
Exchange of pieces to create new strain
Creates antigenic shift

Question 22

What is the cause of viral antigenic drift?

Answer 22

Mutations

Question 23

What is the cause of viral antigenic shift?

Answer 23

Reassortment

Question 24

What is a viral quasi-species?

Answer 24

Group of non-identical but interactive sequence which compete in a highly mutagenic environment with selective pressure

Question 25

Describe with examples how one flu can cause multiple epidemics.

Answer 25

Escape mutants = Spanish, Russian flus with H1N1.

Question 26

Name some criteria used to classify viruses

Answer 26

Nucleic acid
Symmetry of capsid
Enveloped or not
Genome architecture
Baltimore class