POS - Virology

Question 1

What is a virus?

Answer 1

An obligate intrcellular parasite

Question 2

What does it need?

Answer 2

A host cell

Question 3

What are the details?

Answer 3

Very small - need electron microscope to visualise

Lacks organelles - no nucleus, mitochondria or ribosomes

Question 4

What is the structure of a naked/un enveloped virus?

Answer 4

Capsid surrounding viral nucleic acid and viral enzymes

Question 5

What is the structure of an enveloped virus?

Answer 5

Lipid bilayer with viral envelop protein surrounds the capsid

This surrounds the viral nucleic acid and viral enzymes

Question 6

What is the virus envelope made of?

Answer 6

Host derived lipid bilayer
Virus encoded glycoproteins, which form spikes and protrude from virus surface.

Question 7

How do you classify a virus with its structure?

Answer 7

Genome structure and composition

Structure and symmetry of the capsid

Presence or absence of an envelope

Question 8

How do you split viruses depending on their genome?

Answer 8

DNA - double stranded DNA virus or single stranded DNA virus with some circular.

RNA - double stranded RNA or single stranded RNA. This ssRNA then splits to positive - translated directly to proteins or negative - has to be translated to positive before translated to proteins.

Question 9

Whats an example of ssDNA viruses?

Answer 9

Parvoviridae
Circoviridae

Question 10

Whats an example of dsDNA viruses?

Answer 10

Poxviridae
Herpesviridae
Papillomaviridae
Adenoviridae
Papovaviridae

Question 11

What are DNA viruses?

Answer 11

All monopartite (all viral genes on a single segment)

Mostly ds

Few circular

Little diversity

Question 12

What are RNA viruses?

Answer 12

Mostly ss

All linear

Can have more than one segment

Question 13

What are examples of dsRNA?

Answer 13

Reoviridae
Birnaviridae

Question 14

What are examples of +ve ssRNA?

Answer 14

Coronaviridae
Picornaviridae
Arteriviridae
Flaviviridae

Question 15

What are examples of -ve ssRNA?

Answer 15

Paramyxoviridae or Orthomyxoviridae

Question 16

What enzyme do RNA viruses need to take with them?

Answer 16

RNA polymerase to copy the genome so are dependent

Question 17

Why are RNA polymerases error prone and what are the consequences of this?

Answer 17

No proof reading and this makes the viruses more variable and able to evolve rapidly.

Question 18

Why are RNA viruses segmented?

Answer 18

To allow reassortment to increase diversity

eg. bluetongue and influenza

Question 19

How do RNA viruses reassort?

Answer 19

Mix genes during replication, requiring simultaneous infection of different strains

2 strains of different virus infect and due to reassortment there can be new progeny.

Question 20

What are the three types of capsid structure?

Answer 20

Icosahedral

Helical

Complex

Question 21

What is the icosagedral capsid look like?

Answer 21

Regular, strong and compact

12 vertices, with 20 triangular sides (5,3 and 2 symmetry)

Composed of capsomers

Most without envelop

Question 22

What is a capsomer?

Answer 22

The basic building block of a capsid made of repeating protein units.

Either penton or hexon.

Question 23

What is an example of a non-enveloped icosahedral virus?

Answer 23

Parvoviridae

12 capsomers, 60 copies 3 proteins VP2. Extremely stable

Question 24

What is a helical capsid?

Answer 24

A single capsid protein in a spiral configuration. All are enveloped.

Question 25

What is an example of an enveloped helical capsid virus?

Answer 25

Paramyxoviridae - ssRNA, spherical and much larger e.g. canine distemper Rhabdoviridae - bullet shaped with spike like projections e.g. rabies

Question 26

What is a complex capsid?

Answer 26

Asymmetrical and neither helical or ocosahedral

Question 27

Whats an example of a complex capsid virus?

Answer 27

Pox viruses - large enveloped dsDNA, brick shaped or ovoid virion e.g. orf.

Question 28

What are naked viruses?

Answer 28

Icosahedral capsid e.g. adenovirus

Question 29

What are enveloped viruses?

Answer 29

Few icosahedral e.g. icosahedral All helical are enveloped e.g helical Mammalian complex are enveloped e.g. pox

Question 30

What are characteristics of enveloped viruses?

Answer 30

Pleomorphic ( not regular shape) Has host derived lipid bilayer and embedded viral glycoproteins Contain receptors needed for virus entry

Question 31

How do enveloped viruses aquire an envelope?

Answer 31

As they bud through the host membrane (except poxvirus)

Question 32

How are naked viruses released?

Answer 32

By lysis

Question 33

What are the biological properties of enveloped viruses?

Answer 33

More fragile so more easily destroyed by GIT, detergents, disinfectants and outside environment. Needs to stay wet so not likely spread Cause persistent infections (doesnt kill cell) Needs receptors on the envelop to enter

Question 34

What are the biological properites of unenveloped viruses?

Answer 34

Environmentally stable to temp, drying out, pH, detergents and proteases. Easily spread and can survive drying out. Has to kill cell via lysis

Question 35

What are structural viral proteins?

Answer 35

Capsid proteins Envelope proteins Matrix protein (layer inside envelope and outside capsid) Virion-associated enzyme

Question 36

What are non-structural proteins/

Answer 36

Often enzymes involved in replication cycle Some regulatory proteins, oncoproteins etc.

Question 37

What is the function of virus capsid proteins?

Answer 37

Protect the viral nucleic acid Capsids contain receptors that attach to host cell to allow entry

Question 38

What are the function of virus envelope proteins?

Answer 38

Often glycosylated, embedded proteins. Contain preceptors to attach to a permissive host cell receptor Targes of host immune response Interact with capsid during virus assembly

Question 39

What are the function of viral matrix proteins?

Answer 39

Connects envelope with the virus capsid. Crucial in interaction and assembly Found in paramyxovirus, orthomyxoviruses, herpesvirus and retrovirus

Question 40

What is the function of enzymes that are structural proteins?

Answer 40

RNA viruses carrying own RNA polymerase as a structural protein Seen in all -ve sense RNA viruses

Question 41

What is the function of non structural viral proteins?

Answer 41

Made in virus-infected cell, often enzymes involved in viral replication (proteases, helicases, polymerase and protein primers) Help proteins avoid host immune response Targets T cell epitopes.