Viruses Flashcards
How big are viruses?
Submicroscopic- 18-350nm
What is required to see viruses?
An electron microscope
What is meant by viruses being obligate intracellular parasites?
They can’t independently replicate
Why are viruses obligate intracellular parasites?
- They have no genes that encode proteins that function as metabolic machinery for energy generation
- Can’t obtain molecules form which energy can be yielded
- Have no genes that encode proteins that function as metabolic machinery for protein synthesis
- May or may not contain genes that encode for enzymes involved in nucleic acid synthesis
- May or may not have proteins processing nucleic acid
What is the significance of some viruses having proteins processing nucleic acids?
They can be used as targets for antiviral drugs
What is the genetic material in viruses?
DNA or RNA, not both
Which of the types of viruses, DNA or RNA, are more stable?
DNA
Why are DNA viruses more stable?
RNA is less genetically stable
What is the result of RNA being less genetically stable?
RNA viruses mutate faster than DNA viruses
Do viruses have small ions or polysaccharides?
No
Do viruses contain lipids?
Enveloped viruses do, naked viruses do not
What is the significance of naked viruses?
They are harder to destroy by heat or disinfectant
Give 4 viral shapes
- Adenovirus
- Papillomavirus
- Parvovirus
- Morbillovirus
Why are viral shapes important?
Because we can design drugs that directly fit the virus
Describe the growth curve of bacteria
Logarithmic, steady, exponential
Explain the growth curve of viruses
Low levels until the cell bursts, releasing a huge number of viruses
What are more difficult to control, bacterial or viral infections?
Viral
Why are viral infections more difficult to control than bacterial?
Because virus numbers are 3 orders of magnitude bigger
What is the genetic information for a virus?
Nucleic acid of RNA or DNA
Describe the genetic information for viruses
NAME?
What does segmented genetic information allow?
Reassortment, so can get lots of different strains
What can be if there is SS RNA?
Can be of plus or minus sense
What can happen if there is +RNA?
Genomic RNA can serve as mRNA, and so be directly translated into protein
Can genomic RNA serve as mRNA if it is of a - sense?
No
How is specific diagnosis of most viral infections achieved?
Molecular detection of their genomes
What is a long term survival strategy for viruses?
Converting RNA to DNA
What does the conversion of RNA to DNA require?
Reverse transcriptase
What is a virion?
A viral particle
Essentially, what is the envelope in an enveloped particle?
The host cytoplasmic membrane
What do all viruses have?
A nucleocapsid
What is the nucleocapsid?
A protein coat the encloses and protects the genomic material
How many protein types are in the nucleocapsid?
1, 2 or 3
What is true of the proteins that made up the nucleocapsid?
They are complementary units, and so stick together naturally
What are individual sub-units of nucleocapsids called?
Capsomeres
What is a nucleocapsid without a genome?
A capsid
What are the functions of the capsid?
- Protects delicate inner nucleic acid from harsh environmental conditions
- May be involved in attachment to host cells
What are the two basic capsid structures?
- Icosahedral
- Helical
What can capsomers be used to make?
- Vaccines
- Antibodies to make diagnosis of viral infection
What proteins to viruses encode for?
Ones that can naturally insert into host cell membrane
What do the viral proteins inserted into the cell membrane allow?
The viral capsid to recognise part of the host membrane, which can then bud out to produce enveloped viruses
What are the most numerous biological entities on the planet?
Bacteriophage T4-complex virus
What are bacteriophage T4-complex viruses involved in?
Transfer of drug resistance
How are bacteriophage T4-complex viruses involved in drug resistance?
They carry some of the proteins that enable bacteria to carry infection
How do the viruses that infect human cells compare to those that infect bacteria?
Relatively similar
What are the requirements for viral infection and replication in the host cells?
- Cell must contain the receptor the virus binds to in the process of initiating infection
- In order for virus to successfully replicate in host cells, the host cell must have cellular machinery the virus needs for replication
Why can viruses only target specific cells/species?
Because the surface of the virus must come into contact with receptor in host cell, but the receptor might not be on all host cells
What is the part of the virus that binds to the receptor called?
The ligand
Where is the ligand found?
NAME?
Is there a one ligand-one receptor relationship?
No
What is the result of the possibility for multiple receptors for one ligand?
Complexities of some things that they cause
What is the host range of a virus?
The spectrum of host cells that the virus can successfully infect and replicate in
What is said if a virus successfully replicates in a host cell?
The infection is productive, and the host cell is permissive for virus
What can sometimes happen when a cell produces viral particles?
The particles cannot infect new cells, which is an immunological advantage
What is the most commonly used scheme for viral classification?
Baltimore scheme
What is the Baltimore scheme based on?
Relationship between viral genome and the mRNA used for translation during expression of viral genome
What do we use as the main classification in medical virology?
The nucleic acid type and envelope
What are generally more susceptible to disinfection?
Enveloped viruses
What are effects of a virus on the host cell?
Cytopathic effects, and cell death
When does a virus usually cause cell death?
On release of the virus
What are cytopathic effects?
Visible effects on the host cells caused by viral replication
Give 4 cytopathic effects
- Inclusion bodies
- Syncytia formation
- Chromosomal damage
- Inhibition of host cell protein, RNA or DNA synthesis
Where do inclusion bodies occur?
At the site of active virus synthesis
Give an example of an inclusion body
Negri bodies in the rabies virus
What are synctias?
Giant, multinucleated cells formed by the fusion of plasma membranes
What causes chromosomal damage?
Viral nucleic acid can get into nucleus and integrate into host DNA
What do many enveloped viruses produce regarding cytopathic effects?
No direct light microscope observable effects
What does the development of cancer from viruses require?
That the virus integrates all of part of its genome into the host cell DNA
What kind of viruses can cause cancer?
Only RNA viruses that are retroviruses
How do RNA retroviruses cause cancer?
They bring in or turn on cellular oncogenes that cause cells to proliferate uncontrollably
Can DNA viruses cause cancer?
Yes, but usually do so in a non-permissive cell
What is meant by a non-permissive cell with regards to viral cancer?
A cell that lacks something required for viral growth
How do DNA viruses usually cause cancer?
By inactivating tumour suppressor proteins that normally cat to keep the cell from going through the cell cycle, therefore the cell starts going through the cell cycle and proliferating
What is a lot of what happens in infectious disease due to?
Overreaction of the immune system
What are a lot of infectious disease treatments aimed at?
To stop the overreaction of the immune system
What happens in people who are immunocompromised?
- They don’t have the same symptoms as a normal person, so the diagnostic criteria must be changed
- Will die much quicker because pathogen not being suppressed by immune system
What happens in Ebola?
The virus both reduces the effective immune response, and enhances unproductive inflammation
What do the complex interactions that occur in Ebola lead to?
Coagulation failure and the haemohagic picture
What is the specific immune response to a disease often used as?
An alternative method of diagnosis to genome production
What are the possible states of a virus?
- Acute
- Subacute
- Chronic
- Latent
Where can viruses be obtained from?
NAME?
What are the direct contact routes for viral infection?
- Sexual contact
- Vertical transmission
- Environmental routes
- Respiratory
- Gastrointestinal
- Transcutaneous
What are viral infections characterised by?
Incubation period in which virus replication that eventually leads to damage/dysfunction that is symptomatic
Where can a virus spread to?
NAME?
How do many viruses spread?
Via multiple pathways
How can viruses be detected?
- Genome directed nucleic acid amplification (NAA)
- Culturing in cell cultures
- Identification of virus particles or antigens in tissue specimens
- Detecting specific virus-directed immune response
