Block D Lecture 1: Introduction to Virology

Question 1

How did viruses used to be classified?

Answer 1

By the disease type they cause
(Slide 2)

Question 2

What are the 5 different classes in disease based virial classification?

Answer 2

Enteric viruses
Arboviruses
Respiratory viruses
Hepatitis viruses
Sexually transmitted viruses

(REMEMBER EARTHS WITHOUT THE T - EARHS)
(Slide 2)

Question 3

What are enteric viruses?

Answer 3

E.g polio, rotaviruses, reoviruses and some adenoviruses - cause gastric infections
(Slide 2)

Question 4

Where do enteric viruses replicate?

Answer 4

In the gut
(Slide 2)

Question 5

How are enteric viruses acquired?

Answer 5

By ingestion of faecal-contaminated material
(Slide 2)

Question 6

What are arboviruses?

Answer 6

e.g - flaviruses, bunyavirus and some rhabdoviruses - they infect insects that ingest vertebrate blood and then replicate in the tissue of the insect and become transmitted to the vertebrate host
(Slide 2)

Question 7

What are respiratory viruses?

Answer 7

E.g influenza, rhinoviruses, adenoviruses, usually acquired by inhalation of droplets
(Slide 2)

Question 8

What are hepatitis viruses?

Answer 8

All viruses that cause liver disease
(Slide 2)

Question 9

Where do respiratory viruses replicate?

Answer 9

Usually in the respiratory tract
(Slide 2)

Question 10

What type of viruses are easiest to grow?

Answer 10

Bacterial viruses
(Slide 3)

Question 11

How can animal viruses (and some plant viruses) be cultivated?

Answer 11

In tissue or cell cultures
(Slide 3)

Question 12

Why are plant viruses usually the hardest to grow?

Answer 12

As they often require the growth of a whole plant in order to be studied
(Slide 3)

Question 13

What does a titer refer to?

Answer 13

The number of infectious units per volume of fluid
(Slide 3)

Question 14

What is a plaque assay?

Answer 14

It is analogous to the bacterial colony and is one way to measure virus infectivity
(Slide 3)

Question 15

What does each plaque result from?

Answer 15

Infection by a single virus particle
(Slide 3)

Question 16

What are viruses without membranes called?

Answer 16

Naked viruses
(Slide 7)

Question 17

What does a virion consist of?

Answer 17

A nucleic acid packaged into a protein coat (known as a capsid)
(Slide 8)

Question 18

What is a nucleic acid and protein packaged into a virus particle called?

Answer 18

The nucleocapsid
(Slide 8)

Question 19

What does lysozyme do?

Answer 19

Makes a hole in the cell wall and lyses bacteria
(Slide 9)

Question 20

What are neuraminidases?

Answer 20

Enzymes that cleave glycosidic bonds which allows liberation of viruses from the cell
(Slide 9)

Question 21

How are viruses classified today and what is this classification called?

Answer 21

Baltimore classification - viruses are classified based on how they replicate
(Slide 11)

Question 22

What are the 7 classes of viruses in the Baltimore classification?

Answer 22

I - dsDNA
II - ssDNA (+) sense
III - dsRNA
IV - ssRNA (+) sense RNA
V - ssRNA (-) sense
VI - ssRNA (+) sense with dsDNA intermediate
VII - dsDNA with RNA intermediate
To help remember - 3 with DNA - 4 with RNA + one with dsDNA intermediate
(Slide 11)

Question 23

What is the equivalent of the “lag” phase in a one step growth experiment involving viruses?

Answer 23

Latent period
(Slide 12)

Question 24

What comes after the latent period in a one step growth experiment?

Answer 24

Assembly + Release
(Slide 12)

Question 25

What are the 3 main stages of virial replication?

Answer 25

Initiation Replication Release (Slide 13)

Question 26

What are the 4 substages in the initiation stage of virial replication?

Answer 26

Recognition Attachment Penetration Uncoating (Slide 13)

Question 27

What are the 4 sub-stages of replication stage of virial replication?

Answer 27

Transcription Protein synthesis Genome replication Assembly (Slide 13)

Question 28

What are the 3 different mechanisms of release in virial replication?

Answer 28

Lysis and release (naked viruses) Exocytosis Budding and release (for non-naked viruses only) (Slides 13 and 23)

Question 29

What are the early and late phases of virial replication?

Answer 29

Early phase covers initiation stage of virial replication Late phase covers replication and release stages (Slide 13)

Question 30

What are the 3 possible things which a virial attachment protein could be?

Answer 30

The capsid, a protein which extends from the capsid, or glycoproteins of enveloped viruses (Slide 14)

Question 31

What are the steps of pore-mediated penetration (also known as viropexis)?

Answer 31

1. Attachment 2. Pore mediated penetration 3. Viral genome gets inserted into plasmid (Slide 16)

Question 32

What kind of viruses can undergo pore-mediated penetration (viropexis) ?

Answer 32

Naked viruses (Slide 16)

Question 33

What occurs in virial endocytosis?

Answer 33

The virus attaches to the host cell and can then enter it via endocytosis (Slide 17)

Question 34

What 2 virus types can undergo virial endocytosis?

Answer 34

Naked and enveloped (Slide 17)

Question 35

What occurs in membrane fusion involving viruses?

Answer 35

The virus fuses membrane with the cell to insert its genome (Slide 17)

Question 36

What is the difference between DNA and RNA dependent DNA polyremase?

Answer 36

DNA dependent - copies DNA and makes DNA RNA dependent - copies RNA and makes DNA (reverse transcriptase) - always results in DNA being formed (Slide 18)

Question 37

Where does transcription of the genes of DNA viruses occur?

Answer 37

In the nucleus (excluding poxviruses) (Slide 19)

Question 38

Why are DNA virus's virial regulatory regions similar to that of the hosts?

Answer 38

By mimicking host regulatory sequences, DNA viruses can hijack the host cell's transcriptional machinery to regulate the expression of viral genes and facilitate viral replication (Slide 19)

Question 39

What is the difference between DNA and RNA dependent RNA polyremase?

Answer 39

RNA dependent - copies RNA and makes RNA (RNA viral replication) DNA dependent - copies DNA and makes RNA (transcription) - always results in RNA being formed (Slide 18)

Question 40

What is a smaller virus more dependant on?

Answer 40

It's host (Slide 19)

Question 41

What do many DNA viruses promote?

Answer 41

Cell growth (Slide 19)

Question 42

What kind of mRNA is transcribed first in DNA viruses?

Answer 42

mRNA for non-structural proteins -(early phase proteins)

Question 43

What initiates transcription of late phase genes in DNA virial replication?

Answer 43

Genome replication (Slide 19)

Question 44

Where is DNA replication initiated?

Answer 44

The origin (Replication origins) (Slide 19)

Question 45

What must be virus encoded (made by the virus) for use in RNA virus replication?

Answer 45

Polymerase enzymes (Slide 20)

Question 46

Where does replication of RNA viruses occur?

Answer 46

In the cytoplasm (excluding influenza) (Slide 20)

Question 47

What are RNA viruses more prone to?

Answer 47

Mutation (Slide 20)

Question 48

What kind of mRNA are eukaryotic ribosomes unable to translate?

Answer 48

Polycistronic mRNA (Slide 21)

Question 49

What is polycistronic mRNA?

Answer 49

mRNA which contains coding sequences of multiple proteins (Slide 21)

Question 50

What are the 2 main morphologies of viruses?

Answer 50

Helical and icosahedral viruses (Slide 22)

Question 51

What occurs in virial exocytosis?

Answer 51

The new virions are transported to the cell membrane and either their envelopes, or just their membranes fuse with the host membrane to allow release from the cell (Slide 23)