Viruses

Dec 09, 2020 08:19 AMA virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to bacteria and archaea. Bacteriophage is a special case virus. (Lives inside a bacteria) .

Virus particles (known as virions) consist of two or three parts: i) the genetic material made from either DNA or RNA, long molecules that carry genetic information; ii) a protein coat that protects these genes; and in some cases iii) an envelope of lipids that surrounds the protein coat when they are outside a cell. The shapes of viruses range from simple helical and icosahedral forms to more complex structures. The average virus is about one one-hundredth the size of the average bacterium. Most viruses are too small to be seen directly with an optical microscope.

Virus classification is the process of naming viruses and placing them into a taxonomic system. Similar to the classification systems used for cellular organisms, virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which is to say they are non-living particles with some chemical characteristics similar to those of life. As such, they do not fit neatly into the established biological classification system in place for cellular organisms.

Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause. Currently, two main schemes are used for the classification of viruses: the International Committee on Taxonomy of Viruses (ICTV) system and Baltimore classification system, which places viruses into one of seven groups. Accompanying this broad method of classification are specific naming conventions and further classification guidelines set out by the ICTV.

Viruses can be classified by the type of RNA or DNA they contain (as above right). That is the Baltimore Classification. See below

In the Baltimore Classification viruses can be: 

I: dsDNA viruses (e.g. Adenoviruses, Herpesviruses, Poxviruses)

II: ssDNA viruses (+ strand or "sense") DNA (e.g. Parvoviruses)

III: dsRNA viruses (e.g. Reoviruses)

IV: (+)ssRNA viruses (+ strand or sense) RNA (e.g. Coronaviruses, Picornaviruses, Togaviruses)

V: (−)ssRNA viruses (− strand or antisense) RNA (e.g. Orthomyxoviruses, Rhabdoviruses)

VI: ssRNA-RT viruses (+ strand or sense) RNA with DNA intermediate in life-cycle (e.g. Retroviruses)

VII: dsDNA-RT viruses DNA with RNA intermediate in life-cycle (e.g. Hepadnaviruses)

There are two main cycles of viral infection, the lytic cycle of viral infection and the lysogenic cycle of viral infection. The modern viruses of today are also more complex than just lytic or lysogenic viruses.

April 2017--

Scientists from the US and Austria, including a Greek microbiologist, discovered a group of giant viruses that they named “Klosneuviruses”.

The first giant virus, Mimivirus, was discovered in 2003 by a team of French microbiologists. Since then these micro-organisms that are considerably bigger than the common viruses deeply attract the scientists who in the meanwhile have found more groups of such viruses (Mamavirus, Megavirus and Pithovirus).

The study of the new mega-virus indicates that the giant viruses appear to have evolved from smaller viruses by gaining (or stealing), in their evolution course, hundreds of genes from other cells when the common viruses have only a few number of genes (HIV or AIDS virus has only nine genes when the Mimivirus 1,018, approx 1.2 million bp, and the Klonsneuvirus approximately 700 genes). Pandora virus is 2.8 million bp. Pandora is larger than some bacteria.

See paper on viruses creating the nucleus. Opposite. <img src="/c135f530-b61a-5c7a-8b62-0a4327160f8f.png"/>   <img src="/a3956a6d-0930-5921-9239-79925ffd35ee.png"/>

Viruses

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