What is a Virus ?

6  Virus comes from the Latin word for “poison” or “slimy liquid,” an apt descriptor for the bug that causes flu and the common cold.

It was so large and complex, they initially assumed it was a bacterium.

Viruses Infect Plant, Animal, and Bacterial cells
Viruses can infect bacterial and eukaryotic cells. The most commonly known eukaryotic viruses are animal viruses, but viruses can infect plants as well. These plant viruses usually need the assistance of insects or bacteria to penetrate a plant's cell wall. Once the plant is infected, the virus can cause several diseases which usually do not kill the plant but cause deformation in the plant's growth and development.

7  In 1992 scientists tracking a pneumonia outbreak in England found a massive new kind of virus lurking within an amoeba inside a cooling tower. It was so large and complex, they initially assumed it was a bacterium.

A virus that infects bacteria is known as a bacteriophages or phage. Bacteriophages follow the same life cycle as eukaryotic viruses and can cause diseases in bacteria as well as destroy them through lysis. In fact, these viruses replicate so efficiently that entire colonies of bacteria can be destroyed quickly. Bacteriophages have been used in diagnosis and treatments of infections from bacteria such as E. coli and Salmonella.

8  That über-virus is now called Mimivirus, so named because it mimics bacteria and because French biologist Didier Raoult, who helped sequence its genome, fondly recalled his father telling the story of “Mimi the Amoeba.”

That über-virus is now called Mimivirus, so named because it mimics bacteria and because French biologist Didier Raoult, who helped sequence its genome, fondly recalled his father telling the story of “Mimi the Amoeba.”

9  Mimivirus contains more than 900 genes, which encode proteins that all other viruses manage to do without. Its genome is twice as big as that of any other known virus and bigger than that of many bacteria.

Some Viruses Use Human Proteins to Infect Cells
HIV and Ebola are examples of viruses that use human proteins to infect cells. The viral capsid contains both viral proteins and proteins from the cell membranes of human cells. The human proteins help to 'disguise' the virus from the immune system.

Mimivirus contains more than 900 genes, which encode proteins that all other viruses manage to do without

10  Mamavirus, closely related to Mimivirus but even bigger, also turned up inside an amoeba in a Paris cooling tower. (Maybe somebody should clean those towers.)

Retroviruses Are Used in Cloning and Gene Therapy
A retrovirus is a type of virus that contains RNA and that replicates its genome using an enzyme known as reverse transcriptase. This enzyme converts the viral RNA to DNA that can be integrated into the host DNA.

Its genome is twice as big as that of any other known virus and bigger than that of many bacteria.

11  Mamavirus is so big that it has its own dependent, a satellite virus named Sputnik.

The host then uses its own enzymes to translate the viral DNA into viral RNA used for viral replication. Retroviruses have the unique ability to insert genes into human chromosomes. These special viruses have been used as important tools in scientific discovery. Scientists have patterned many techniques after retroviruses including cloning, sequencing, and some gene therapy approaches.

Mamavirus, closely related to Mimivirus but even bigger, also turned up inside an amoeba in a Paris cooling tower. (Maybe somebody should clean those towers.)

12  Amoebas turn out to be great places to seek out new viruses. They like to swallow big things and so serve as a kind of mixing bowl where viruses and bacteria can swap genes.

13  Viruses are already known to infect animals, plants, fungi, protozoa, archaea, and bacteria. Sputnik and Mamavirus suggest that they can infect other viruses, too.

Mamavirus is so big that it has its own dependent, a satellite virus named Sputnik.

14  In fact, scratch the whole concept of “us versus them.” Half of all human DNA originally came from viruses, which infected and embedded themselves in our ancestors’ egg and sperm cells.

Amoebas turn out to be great places to seek out new viruses. They like to swallow big things and so serve as a kind of mixing bowl where viruses and bacteria can swap genes.

15  Most of those embedded viruses are now extinct, but in 2005 French researchers applied for permission to resurrect one of them. Some scientists objected, saying the resurrected virus could go on a rampage; the research ministry approved the project.

Viruses are already known to infect animals, plants, fungi, protozoa, archaea, and bacteria. Sputnik and Mamavirus suggest that they can infect other viruses, too.

16  Apocalypse Not: The virus, dubbed Phoenix, was a dud.

In fact, scratch the whole concept of “us versus them.” Half of all human DNA originally came from viruses, which infected and embedded themselves in our ancestors’ egg and sperm cells.