Lecture 17 Flashcards
What features of viruses make them obligate parasites?
They are unable to produce the energy or proteins necessary for replication
Can a viral genome contain both DNA and RNA?
No, it make contain EITHER DNA or RNA but not both
What features of virus replication prevents it from being considered living?
Viruses are assembled from components rather than replication through division like bacterial or human cells
Can the sterilization process of micro filtration remove viruses?
No as they are filterable agents
How can viruses be classified?
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
What is an abrovirus?
A virus which is spread via insects
What is a toga virus?
A virus which has a mantle and an envelope
What components make up the basic structure?
A capsid coat composed of capsomers
And nucleic acids
What are the two forms of morphology that capsids can take?
Helical or Polyhedral
What are capsomers?
Proteinaceous subunit
What additional features do only some viruses contain?
The lipid envelope
What are the spikes seen in viruses when it is observed through an electron microscope and what is their function?
They are protein structures used for host binding and are usually very specific resulting in only a narrow spectrum of hosts
What are the properties of a naked capsid virus?
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
What are the properties of viruses which have envelopes?
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
What is the advantage of viral envelopes?
The host cell does not need to be killed in order for the virus to replicate
What are the requirements of all RNA viruses?
They must contain genes for replication of the RNA and/or conversion of RNA to DNA
What are the differences between sense RNA (+) and missense RNA (-)
+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
What are bacteriophages?
Complex viruses that only infect bacteria
What are the differences between a virus and bacteriophage?
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
What are the similarities between bacteriophages and viruses?
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
What is the progression of viral infection?
- Acquisition (entry into body)
- Initiation of infection (at primary site)
- Incubation period (virus amplifys and spreads)
- Replication in target tissue resulting disease occurring
- Immune responses both limit and contribute to the disease
- Virus production in tissue, release, contagion
- Resolution or persistent infection/chronic disease
What is a Latent virus infection?
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
What are three examples of latent virus infections?
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
What are oncogenic viruses?
Viruses which can cause cancer by inserting themselves close to a proto-oncogene, when the virus is activated so is the oncogene causing cancer
What are three examples of oncogenic viruses?
Epstein-Barr Virus: Burkitts Lymphoma
Human Papillomaviruses: Cervical Cancer
Human Herpesvirus8: Karposi Sarcoma
What are viroids and prions?
Viroids are small naked sections of single stranded RNA which infects plants
Prions are small infectious proteins which cause neurological disease
What are three examples of prion disease?
Scrapie (Sheep)
Bovine Spongieform encephalopathy (mad cow disease)
Creutzfeld-Jakob disease (CJD, Humans)
What are the methods of viral transmission?
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)
How are viruses treated?
With antiviral drugs which are limited to only small range of viruses, with some viruses having resistance
Antibiotic treatments are NOT effective
