MODULE 1

Question 1

What two characteristics of viruses differ from bacteria such that tobacco mosaic virus was identified as non-bacterial?

Answer 1

Transmitted through a bacteria-proof filter, can’t be cultivated as a pure substance (require host)

Question 2

What is multiplicity of infection and how do high and low MOI viruses escape the cell?

Answer 2

Multiplicity of infection: ratio of virus to host cell
At a low MOI, viruses multiply inside the host and lyse from within.
At a high MOI, viruses weaken the wall as they enter and lyse from without

Question 3

What are the three phases of the one-step growth curve?

Answer 3

Eclipse phase: virus attaches and uncoats
Maturation phase: infectious progeny is assembled within the host
Latent phase: time between innoculation and release of first infectious virus

Question 4

What experiment showed that nucleic acid is the carrier of viral heredity

Answer 4

Hershey-Chase experiment

Question 5

What experiment showed that RNA is the genetic material of plants?

Answer 5

Fraenkel-Conrat experiment

Question 6

What are the steps of the viral multiplication cycle?

Answer 6

1. Attachment: proteins reversibly bind to receptors via week electrostatic interactions
2. Penetration: virus gains entry to the cell
3. Un-coating: loss of many/all viral proteins
4. Biosynthesis: replication, transcription and translation of viral DNA
5. Assembly: newly synthesized viral proteins and nucleic acid form new viruses
6. Release: progeny viruses leave the host cell

Question 7

Why is there a limited number of designs for viral structure?

Answer 7

1. For efficiency: no complex shapes for rapid assembly

2. For stability: exist in tumultuous environment, require a structure that is highly adaptable/generalized

Question 8

Capsomere

Answer 8

protein subunit that makes up the capsid

Question 9

Helically arranged around helical nucleic acid

Answer 9

Filamentous viruses

Question 10

Cubic symmetry viruses

Answer 10

isometric viruses

Question 11

How many subunits does an icosahedron have?

Answer 11

60

Question 12

What is the envelope made of?

Answer 12

lipid bilayer (ether-sensitive)

Question 13

What are the two types of envelope proteins?

Answer 13

1. Matrix proteins: link internal nucleocapsid to envelope
2. Glycoproteins: transmembrane proteins (external glycoproteins are major antigens; transport channel proteins modify internal environment by moderating passage in and out of cell)

Question 14

What are the possible envelope/capsid combinations?

Answer 14

1. isometric core - isometric envelope
2. helical core - spherical envelope
3. helical core - non-spherical envelope

Question 15

What were the previous 4 ways we could classify viruses?

Answer 15

1. Classification by host
2. Classification by morphology
3. Classification by disease
4. Classification by nucleic acid

Question 16

How can we determine strandedness of viruses?

Answer 16

1. measure UV absorption before and after denaturing and see if the sample is more dense than prior to denaturing
2. measure proportion of purines to pyrimidines

Question 17

Explain the classes of the Baltimore scheme

Answer 17

Class 1: dsDNA
Class 2: ssDNA
Class 3: dsRNA
Class 4: +ssRNA
Class 5: -ssRNA
Class 6: retrovirus ssRNA, DNA intermediate
Class 7: reversivirus dsDNA, ssRNA intermediate

Question 18

What is the difference between a satellite virus and a satellite nucleic acid?

Answer 18

Neither encode replication enzymes, they both require co-infection with a helper virus.
Satellite viruses encode structural proteins.
Satellite nucleic acid encode no proteins or only nonstructural proteins.

Question 19

What is a viroid?

Answer 19

Smallest self-replicating pathogen
Circular ssRNA in plants
Do not have protein (capsid)

Question 20

Why are RNA viruses have more genetic diversity?

Answer 20

No proof-reading mechanism

Question 21

What are quasispecies?

Answer 21

High mutation rates in small DNA and RNA viruses allow for a large number of variant genomes within a species

Question 22

What are the two methods of recombination?

Answer 22

1. Polymerase jumps from one template strand to another

2. Cleavage between two genomes that are then combined

Question 23

Explain the difference between antigenic drift and antigenic shift.

Answer 23

Both are methods of genetic reassortment.
Antigenic shift: a sudden shift in genetic properties by reassortment of segments
Antigenic drift: slow accumulation of mutations

Question 24

What do we call the shift from animal to human host?

Answer 24

Zoonosis

Question 25

What phenomenon do we call it when the virus can never evolve faster than the host?

Answer 25

Red queen hypothesis

Question 26

What does a plaque represent on a plaque assay?

Answer 26

One plaque is a released virus, however it may not represent the entire viral population because it does not account for viruses that haven’t been released from the host yet.

Question 27

How can we detect viruses?

Answer 27

1. Detection by antibody (ELISA)

2. Detection by nucleic acid (PCR)

Question 28

How can we test antibodies?

Answer 28

1. Neutralization assay

2. Antibody capture ELISA

Question 29

What is systems level virology?

Answer 29

When we sequence all the nucleic acid in a large sample and look for novel sequences to detect unknown viruses.