Virology I Flashcards
What is a virus?
An infectious agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy and is able to multiply only within the living cells of a host
In what species can viruses be found?
Viruses can be found in different hosts;
Humans
Animals
Plants
Bacteria
Although, sometimes viruses of humans and animals are thought of as viruses of mammals and non-mammals or vertebrates and invertebrates
Importantly some viruses can move between hosts
For example; viruses from animals can be transmitted directly to humans
Or the same virus can move between insects, humans and animals
Where a virus is found can be described as its “host range”
In what tissues and organs can viruses be found?
Viruses can be found in multiple tissues and organs of their host
The tissues that viruses can be found in can be referred to as their “tissue tropism”
Through processes of evolution viruses evolve to replicate in tissues that favour transmission of between hosts and allow them to evade the immune system of the host
For example, some viruses replicate in the lungs and are transmitted in the air by breathing, coughing and sneezing
Some viruses replicate in tissues required for pro-creation and are transmitted by sexual intercourse
For example; some viruses replicate in cells of the immune system, preventing immune function
Some viruses choose not to replicate immediately and cannot be detected by the immune system
What are the differences between viruses, bacteria and prions?
Virus: an infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host
Viruses, bacteria and prions are all infectious and too small to be seen under a microscope
Bacteria contain nucleic acid (DNA) covered in protein, have a polysaccharide cell wall (a coat of sugar molecule) and can replicate outside of the cell
Prions are proteins, do not contain nucleic acid and replicate inside the cell
Viruses are nucleic acid (DNA or RNA) covered by proteins, have no cell wall and may or may not have a lipid coat
Viruses must replicate in the cell; they are “obligate cellular parasites”
How does a virus replicate?
Virus enters the cell, the viral DNA is converted to RNA
Virus moves to where DNA is made
Production of new virus and exit of the virus from the cell
RNA virus:
Recognise the host cell and enters the cell through envelope glycoproteins mediated entry
Virus moves to where RNA is made- cytoplasm
Virus of RNA genomes produces more RNA genomes
Packaging step is when the new virus is packaged into new protein coats/shells
Exit from cell through budding or lysis
What are the essential structural features of a virus?
Different viruses have different structures but retain similar organisation
Virus structure can dictate host range and tissue tropism
Different coats have different proteins sticking out of their protein coats which recognise specific cells
