Introduction to Viruses Flashcards
Describe the one basic element of a virus that differentiates it from other pathogenic microorganisms.
Viruses are non-cellular.
They have a genetic element that cannot replicate independently off of a host cell.
Describe the icosahedral structure of a virus.
20 faces, each an equilateral triangle.
Describe the helical structure of a virus.
This is where the protein of the virus binds around the DNA and RNA in a helical fashion.
Describe a “complex” structure of a virus.
Neither icosahedral not helical.
Describe viruses as a obligate intracellular pathogens.
Viruses are classed as obligate intracellular pathogens as they are only capable of replication within the host cell.
The host could be; bacteria, animal or plant.
Describe a virion.
The extracellular form of a virus that facilitates transmission from one host cell to another.
Describe the taxonomy of viruses.
Order
Family
Genus
Species.
List the ways in which virus families can be classified.
Virion
Presence/absence of envelope
Genome structure
Mode of replication.
Describe some human infecting viruses of major importance.
Icosahedral - polio, adeno and rhino.
Helical - tobacco mosaic virus.
Describe the process of viral replication.
The virus (in its extracellular virion form) will attach to the cell membrane receptor.
This allows for receptor mediated endocytosis and the sequential release of the capsid into the cytosol.
The viral DNA is released from the capsid and is translocated to the nucleus.
In the nucleus, the viral DNA is transcribed, leading to production of newly synthesised viral proteins.
The viral DNA (genome) is replicated within the nucleus and is released to form the virion, with the newly synthesised proteins.
The virion then buds and is released.
Describe the concept of host range in relation to viruses.
The host range of a virus is important and determines how many species a virus can infect.
If a virus has a larger host range e.g. they can coinfect human, animal or bird strains could lead to recombination and generation of a new strain.
Describe the consequences of viral infections.
Clearance (e.g. measles - long term immunity).
Chronic infection (e.g. HIV, Hep B, Hep C)
Latent infection (herpes virus)
Transformation (Epstein-Barr disease, HPV) - long term infection with altered cellular gene expression.
Explain the concept of viral latency.
Viral latency is the ability of a virus to lie dormant in a host.
The full viral genome is retained in the host cell, BUT its expression is restricted, such that few viral antigen and no viral particles are produces.
Describe the mechanisms by which viral infections can potentially lead to cancer.
Modulation of cell cycle control - driving cell proliferation
Modulation of apoptosis (prevention of programmed cell death)
Reactive oxygen species mediated damage (some persistent viral infections can cause persistent inflammatory processes which lead to cancer via oxygen reactive species).
Describe antiviral therapy
All antiviral therapies are virustatic.
As viruses utilise host cell enzymes in order to replicate, there are limited viral proteins that are potential targets for antiviral drugs.
Toxicity to the host cell is not uncommon, leading to side effects.
Only used in a minority of viral infections
