May, 3rd 2021
HISTORICAL CONTEXT OF VIRUSES
1) Viruses have been associated with diseases for many centuries.
2) Over the last 1000 years: Viruela & Sarampion were brought to America by European settlers and explorers. The Native American population had no immunity, produced a high mortality rate in the population and was an important factor in the destruction of these societies.
3) Over the last 100 years: A new strain of influenza virus (Spanish influenza) killed >20 million people during 1918-1919 in the USA, prior to WWI. A decade later, virus polio became one of the most important viral infections in children and young people.
3) Over the last 25 years: A new virus, VIH, has spread rapidly, causing a worldwide epidemic. Other viruses: SARS, Nile fever virus, Hantavirus, Ebola, avian influenza, etc.
"H1N1 Influenza Virus Particles" by National Institutes of Health (NIH) is licensed under CC BY-NC 2.0
Definition They are entities whose genomes replicate inside cells, using the cell's synthetic machinery, and promote the synthesis of specialized elements for the transfer of their genome to new cells.
30,000 viruses grouped into 3,600 species, in 164 genera and 71 families.
1) They are macromolecular organizations made up of nucleic acids and proteins, some also have lipids and carbohydrates.
2) Submicroscopic particles of variable size, between 10 (parvovirus) and 400 nm (pox virus).
3) Strict intracellular parasites
4) Infect various cell types (animals, plants, bacteria, bacteria).
Charles Molnar y Jane Gair, OpenStax, CC BY-SA 4.0, via Wikimedia Commons
The structure of a virus is simple, yet there is a certain diversity that is used for the classification of these microorganisms.
Guerin, L. (2021). Cytomegalovirus diagram [Illustration]. CK-12., .CC BY-NC 3.0.
1) Genome: Nucleic acid (DNA or RNA)
1.1 ADN: Single strand, double strand and circular (single or double strand).
1.1 ARN: Single strand, double strand and double segmented strand.
2) Capside: Protein shell surrounding the nucleic acid formed by numerous copies of a protein called capsomer.
2.1 Helicoidal Viruses Helical capsids are composed of a single type of protein subunit built up around a central axis to form a helical structure.
Guerin, L. (2021). A helical virus [Illustration]. CK-12., .CC BY-NC 3.0.
1. Nucleic Acid; 2. Virus protein units; 3. Caspid.
2.2 Icosahedral Viruses The symmetry of the icosahedral capsids gives viruses a spherical appearance under the microscope, but the protein subunits are actually arranged in a regular geometric pattern similar to a soccer, not actually spherical.
Guerin, L. (2021). Adenovirus, an icosahedral virus. An icosahedron is a three-dimensional shape composed of 20 equilateral triangles. [Illustration]. Wikipedia.
2.3 Complex Viruses Complex viruses possess a capsid that is neither strictly helical nor icosahedral and may have more structures, such as protein tails or a complex outer wall.
Guerin, L. (2021). This complex "space probe" virus infects Escherichia coli bacteria [Illustration]. CK-12., .CC BY-NC 3.0.
3) Nucleocapside: Capsid + genome
4) Membranous wrapping: It is only present in "enveloped viruses" and consists of lipoproteins of cellular origin in which glycoproteins are inserted.
Process where the synthesis of nucleic acids and viral proteins takes place in the cytoplasm.
Viruses contain RNA that replicates in the cytoplasm.
Viruses containing DNA replicate in the nucleus.
Proteolytic processing of viral proteins.
Introduction. (n.d.). Retrieved May 1, 2021, from https://bio.libretexts.org/@go/page/40212