1 Virus Classification, Structure, Replication

Question 1

How is a virus different from a bacterium? From a toxin

Answer 1

A virus can’t replicate on it’s own, but it can replicate (unlike toxins)

Question 2

Theories of Virus Origin:

Answer 2

Cellular Origin- evolved from cells

Autopoietic Origin- once autopoietic, became dependent on cells for replication

Question 3

RNA/DNA in a core that is protected by a protein coat. (Virus particle structure)

Answer 3

Nucleocapsid

Question 4

A nucleocapsid is comprised of repeating subunits called _____

Answer 4

Capsomeres

Question 5

Virus-modified cellular membranes acquired upon exit from host.

Answer 5

Envelopes

Question 6

Exposure to lipid solvents in the lab (alcohol, ether, acetone, Freon) render _____ viruses noninfectious

Answer 6

Enveloped

Question 7

Pros/Cons to large virus genome?

Answer 7

Pros- More effective genes/tools

Cons- High chance of error, detection

Question 8

What do most DNA viruses need that RNA viruses do not?

What do RNA viruses need that DNA viruses do not?

Answer 8

DNA polymerase, Nucleus access

Need an RNA dependent RNA polymerase

Question 9

____ is a major factor in virus eradication

Answer 9

Host range

Question 10

_____ is a major determinant of virus tropism (host range)

Answer 10

Attachment

Question 11

Binding of a virus receptor to a cellular receptor.

Answer 11

Attachment

Question 12

Virus entry pathways:

Answer 12

Receptor mediated endocytosis

Direct penetration of plasma membrane

Non-enveloped viruses not well understood (pores, membrane disruption)

Question 13

Influenza entry happens by:

Answer 13

HA protein- attachment and membrane fusion

Question 14

Production of mRNA (messenger RNA) templates for protein synthesis. DNA viruses usually rely on cellular RNA polymerase. The genome of (+)ssRNA viruses can serve as mRNA.

Answer 14

Transcription

Question 15

Production of proteins

Answer 15

Translation

Question 16

Viral protein production can be regulated at the ____ level or the ____ level

Answer 16

Transcript (mRNA)

Translation

Question 17

Genome Replication:

1. Define (+)ssRNA
2. Define (-)ssRNA

Answer 17

1. This genome serves as template for translation; polymerase makes (-)ssRNA copy as template for new genomes
2. Virus practical must include viral polymerase which makes mRNA for translation; this genome replaces through (+)ssRNA intermediate

Question 18

Packaging of new genomes into functional particles.

Answer 18

Assembly

Question 19

Types of Virus Release:

Answer 19

1. Lysis- best known for bacteriophage; viral molecules rupture cellular membrane
2. Weak Lysis- depends on membrane breakdown after cell death
3. Budding (enveloped only)- enveloped viruses use cell membrane as outer coat of virus particle

Question 20

Pros/Cons of Lytic vs Non-lytic infections

Answer 20

Lytic- Dump contents out of cell, has chance to infect other cells before immune system can respond

Non-Lytic- can stay undetected longer

Question 21

How does understanding a virus replication process help to design antivirals?

Answer 21

Find things unique to virus that target it without causing illness to host

Question 22

List the Virus Replication Kinetics curve phases (useful to asses mutations, cell entry, process design):

Answer 22

1. Eclipse- attachment and uptake
2. Exponential growth- replication/assembly
3. Plateau- cell death

Question 23

Cell rounding, syncytia formation, and inclusion bodies would be observations of this infection assay:

Answer 23

Cytopathic Effect (CPE)

Question 24

Infect cells, expose virus antigen, stain with labeled antibody, count areas that flouresce would be observations of this infection assay:

Answer 24

Flourescent Focus Assay

Question 25

Cell monolayer, inoculate with dilute virus, infected cells die leaving a clear area would be observations of this infection assay:

Answer 25

Plaque Assay

Question 26

ID50, IU 50, TCID 50; Systems: tissue culture, eggs, animals; inoculate with different dilutions of virus; calculate concentration based on number infected– these would be observations of this infection assay:

Answer 26

Infectious Dose

Question 27

Direct image of virus particles, calibrate with latex bead standard would be observations of this particle assay:

Answer 27

Electron Microscopy

Question 28

Viruses that bind RBCs, mix constant number of RBCs with various virus dilutions, if virus concentration is sufficient then a matrix of RBCs and virus is formed, matrix does not allow RBCs to pellet–would be observations of this particle assay:

Answer 28

Hemagglutinin Assay

Question 29

DNA primer specific to virus, amplify the gene, very sensitive– would be observations of this genome assay:

Answer 29

Polymerase Chain Reaction

Question 30

Isolate DNA/RNA, separate by electrophoresis, use labeled DNA probe to detect–would be observations of this genome assay:

Answer 30

Southern (DNA) and Northern (RNA) Blots

Question 31

Antibody binding to virus can block infection, virus concentration determined by amount of antibody needed–would be observations of this serological assay:

Answer 31

Virus Neutralization

Question 32

Antibody recognition of virus, amplification by enzyme linked to antibody–would be observations of this serological assay:

Answer 32

ELISA (Enzyme Link Immunosorbant Assay)

Question 33

Separate proteins by electrophroresis, probe proteins using an antibody–would be observations of this serological assay:

Answer 33

Western (Protein) Blot

Question 34

Human viruses have diameters of ____

Answer 34

30-300 nm

Question 35

Viruses are classified by:

Answer 35

1. Genome
2. Virus particle
3. Structure
4. Replication Strategy