Introduction to viruses

Question 1

What is a virion?

Answer 1

Complete virus particle as it exists outside the cell (e.g. with any protein coat and envelope it may possess)

Question 2

What are the main structural components of a virion?

Answer 2

Nucleocapsid

Envelope (not always present)

Question 3

What is a nucleocapsid?

Answer 3

The genome and capsid

Genome = genetic material
- may be ss or ds, RNA or DNA, and linear or circular

Capsid = protein coat for genome

• made up of capsomeres (individual protein molecules)
• may be helical, icosahedral or complex in geometry

Question 4

What is an envelope?

Answer 4

A lipid bilayer - formed from membrane of host cell

Protein and glycoprotein spikes - stick out through envelope

Question 5

What may the protein and glycoprotein spikes assist?

Answer 5

May aid attachment/uptake/uncoating of the virus

Question 6

What form can RNA be translated into a protein?

Answer 6

+ve stranded RNA can be translated directly into a protein by a ribosome

-ve stranded RNA must be transcribed to +ve stranded RNA first

Question 7

What type of viruses are there?

Answer 7

DNA viruses

• ss evnveloped
• ds enverloped
• ds naked

RNA viruses:

• ss -ve enveloped
• ss +ve enveloped
• ss +ve naked
• ds naked

Question 8

Give example of a family of virus with ss enveloped DNA.

Answer 8

Parvoviridae family
e.g. Parvoviridae B19
- causes slapped cheek syndrome (erythema infectiosum)
> rash in kids, may produce temporary arthritis
> dangerous in pregnancy/sick cell

Question 9

What type of virus is the Orthomyxoviridae family and give example(s)?

Answer 9

Single stranded -ve enveloped RNA

- Influenza virus

Question 10

What type of virus is the Paramyxoviridae family and give example(s)?

Answer 10

Single stranded -ve enveloped RNA

• Respiratory synctial virus
• Parainfluenza virus
• Measles
• Mumps

Question 11

What type of virus is the Rhabdoviridae family and give example(s)?

Answer 11

Single stranded -ve enveloped RNA

- Rabies virus

Question 12

What type of virus is the Hepadnaviridae family and give example(s)?

Answer 12

Double stranded enveloped DNA

- Hep B

Question 13

What type of virus is the Herpesviridae family and give example(s)?

Answer 13

Double stranded enveloped DNA

• herpes simplex
• varicella zoster
• CMV
• EBV

Question 14

What type of virus is the Poxviridae family and give example(s)?

Answer 14

Double stranded DNA enveloped

• Molluscum contagiosum
• Variola/Vacinnia (smallpox/cowpox)

Double stranded DNA naked

• Adenovirus
• Papillomavirus

Question 15

What type of virus is the Calciviridae family and give example(s)?

Answer 15

Single stranded +ve naked RNA

- Norovirus

Question 16

What type of virus is the Picornviridae family and give example(s)?

Answer 16

Single stranded +ve naked RNA

• Poliovirus
• Rhinovirus
• Coxsachie virus (hand foot and mouth, gastroenteritis)

Question 17

What type of virus is the Astroviridae family and give example(s)?

Answer 17

Single stranded +ve naked RNA

- astrovirus (causes gastroenteritis)

Question 18

What type of virus is the Flaviridae family and give example(s)?

Answer 18

Single stranded +ve enveloped RNA

- yellow fever

Question 19

What type of virus is the Retroviridae family and give example(s)?

Answer 19

Single stranded +ve enveloped RNA

- HIV

Question 20

What type of virus is the Togaviridae family and give example(s)?

Answer 20

Single stranded +ve enveloped RNA

- Rubella virus

Question 21

What type of virus is the Reoviridae family and give example(s)?

Answer 21

Double stranded naked RNA

- rotavirus (gastroenteritis in kids)

Question 22

What are the six key stages to the viral replication cycle?

Answer 22

Attachment
Penetration
Uncoating
Genome replication and protein production
Assembly
Release

Question 23

How can viruses attach to cells?

Answer 23

2 possible ways:

1) Attachment structures on virion surface (e.g. glycoproteins in spikes)
2) Host receptor molecules (i.e. mimic hormones and fit into host cell receptors)

Question 24

What are the three mechanisms of penetration?

Answer 24

Receptor mediated endocytosis

Membrane fusion

Viral Translocation

Question 25

What occurs during the uncoating stage?

Answer 25

Dissasembly of virus to point where genetic material can be accessed
- involves envelope uncoating and capsid disassembly

Question 26

What are the function of RNA polymerases?

Answer 26

Transcribe DNA into mRNA

Question 27

What are the function of DNA polymerases?

Answer 27

Replicate, i.e. make dsDNA from dsDNA

Question 28

Name four aspects concerned with DNA in capsid replication or protein production.

Answer 28

Early protein production (may be enxymes, proteins to divert host machinery)

Viral DNA production (enabled by early proteins)

Late protein production (necessary for capsid assembly)

Nucleocapsid assembly (from vDNA and capsomeres)

Question 29

How do vRNA make copies of themselves?

Answer 29

They may:

• carry ready made RNA polymerase to copy vRNA
• carry ready made RNA transcriptase to make DNA from vRNA
• contain a gene to produce a vRNA polymerase (only occur in +ve ss or ds RNA viruses)

Question 30

What problem does vRNA have in making copies of themselves?

Answer 30

Unable to make copies of themselves by using host machinery due to mRNA not being copied

Question 31

What is the vRNA to protein ratio for translocation?

Answer 31

One molecule of vRNA may only translate into one protein

Question 32

What occurs during the assembly stage of viral replication?

Answer 32

Nucleocapsid assembled in cytoplasm

Question 33

What occurs during the release stage of viral replication?

Answer 33

Naked viruses:
- can only be released by cell lysis

Enveloped viruses:

• enveloped proteins embed themselves in cell membrane and nucleocapsid associates with membrane
• membrane evaginates forming a vesicle around nucleocapsid which becomes envelope