Lecture 17

Question 1

What features of viruses make them obligate parasites?

Answer 1

They are unable to produce the energy or proteins necessary for replication

Question 2

Can a viral genome contain both DNA and RNA?

Answer 2

No, it make contain EITHER DNA or RNA but not both

Question 3

What features of virus replication prevents it from being considered living?

Answer 3

Viruses are assembled from components rather than replication through division like bacterial or human cells

Question 4

Can the sterilization process of micro filtration remove viruses?

Answer 4

No as they are filterable agents

Question 5

How can viruses be classified?

Answer 5

Structure (size, morphology and nucleic acid)
Biochemical Characteristic (Structure, mode of replication)
Disease Caused
Mode of transmission
Host cell
Tissue or Organ
Location of first isolation
members of a particular family

Question 6

What is an abrovirus?

Answer 6

A virus which is spread via insects

Question 7

What is a toga virus?

Answer 7

A virus which has a mantle and an envelope

Question 8

What components make up the basic structure?

Answer 8

A capsid coat composed of capsomers

And nucleic acids

Question 9

What are the two forms of morphology that capsids can take?

Answer 9

Helical or Polyhedral

Question 10

What are capsomers?

Answer 10

Proteinaceous subunit

Question 11

What additional features do only some viruses contain?

Answer 11

The lipid envelope

Question 12

What are the spikes seen in viruses when it is observed through an electron microscope and what is their function?

Answer 12

They are protein structures used for host binding and are usually very specific resulting in only a narrow spectrum of hosts

Question 13

What are the properties of a naked capsid virus?

Answer 13

They are environmentally stable to temperature, acid, proteases, detergents and drying
this results in viruses being able to remain stable for a long time making them easily spread between people or from objects

Question 14

What are the properties of viruses which have envelopes?

Answer 14

They are environmentally liable, this results in the viruses having more specific requirements to survive including the need to remain wet, and cannot survive in the GI Tract but uses other bodily fluids to spread

Question 15

What is the advantage of viral envelopes?

Answer 15

The host cell does not need to be killed in order for the virus to replicate

Question 16

What are the requirements of all RNA viruses?

Answer 16

They must contain genes for replication of the RNA and/or conversion of RNA to DNA

Question 17

What are the differences between sense RNA (+) and missense RNA (-)

Answer 17

+RNA is read in the same direction as mRNA as the host cell therefore only a gene is required to produce the protein needed for RNA replication
-RNA is read in the opposite direction to the host mRNA therefore the actual protein required for RNA replication is required by the virus

Question 18

What are bacteriophages?

Answer 18

Complex viruses that only infect bacteria

Question 19

What are the differences between a virus and bacteriophage?

Answer 19

The entire virus enters the cell while a bacteriophage only injects its nucleic acid
This means that viruses have a need for uncoating not seen in bacteriophages
Viruses can lyse out of a cell OR simply bud out as opposed to Bacteriophages which can only lyse the cell to spread

Question 20

What are the similarities between bacteriophages and viruses?

Answer 20

Both bind onto a specific receptor
Both use host machinery to express there own genes
Both are assembeld from compnents produced in the hijacked cells

Question 21

What is the progression of viral infection?

Answer 21

1. Acquisition (entry into body)
2. Initiation of infection (at primary site)
3. Incubation period (virus amplifys and spreads)
4. Replication in target tissue resulting disease occurring
5. Immune responses both limit and contribute to the disease
6. Virus production in tissue, release, contagion
7. Resolution or persistent infection/chronic disease

Question 22

What is a Latent virus infection?

Answer 22

Persistent infection where no clinical symptoms occur as the virus does not replicate, occasionally the virus will become activated and cause symptoms these are limited and controlled by the immune response

Question 23

What are three examples of latent virus infections?

Answer 23

Herpes Virus which is a latent infection in neurons activated by fever, stress or sunlight resulting in the formation of cold sores
Chickenpox Virus resurfaces when the immune system weakens by disease or old age causing shingles
HIV this is a latent infection in T calls and macrophages and will cause AIDs

Question 24

What are oncogenic viruses?

Answer 24

Viruses which can cause cancer by inserting themselves close to a proto-oncogene, when the virus is activated so is the oncogene causing cancer

Question 25

What are three examples of oncogenic viruses?

Answer 25

Epstein-Barr Virus: Burkitts Lymphoma
Human Papillomaviruses: Cervical Cancer
Human Herpesvirus8: Karposi Sarcoma

Question 26

What are viroids and prions?

Answer 26

Viroids are small naked sections of single stranded RNA which infects plants
Prions are small infectious proteins which cause neurological disease

Question 27

What are three examples of prion disease?

Answer 27

Scrapie (Sheep)
Bovine Spongieform encephalopathy (mad cow disease)
Creutzfeld-Jakob disease (CJD, Humans)

Question 28

What are the methods of viral transmission?

Answer 28

Aerosols, food, water, fomites (tissues/clothes), direct contact with secretion (saliva, semen), sexual contact, maternal neo-natal, blood transfusion or organ transplants, zoonoses (animals, insects)

Question 29

How are viruses treated?

Answer 29

With antiviral drugs which are limited to only small range of viruses, with some viruses having resistance
Antibiotic treatments are NOT effective