Home Page

The complete history of the Universe -- from the Big Bang to 200 my into the future

Loading

History of the Universe eBook. 398 pages, 300 illustrations only $2.99

Previous pageNext page

Viruses

A virus has no ribosomes, water molecules or cell membrane. It cannot build any proteins itself, so it is not a living thing, but it does contain genetic material, either DNA or RNA, which it can inject into a living cell.

Bacteriophage can inject its genes into a bacterium

Some viruses inject DNA into a cell which is taken into the cellís chromosome. Others inject RNA which is either used by the cellís ribosomes to create new protein or converted first into DNA. Viruses which cause the latter process are called retroviruses.

Once inside the chromosome, the new DNA begins to give out messages for making new viruses. The host cell is thereby turned into a factory for making new copies of the virus.

When it is full of viruses the cell bursts open, sending out millions of viruses to infect more cells.

Size of Viruses

If a soccer ball were blown up to the size of the Earth (Soccearth) then a typical virus would be from 1 meter across (not much bigger than a ribosome) to 20 meters across. On average it would be about the size of a small car.

Origin of Viruses

Nobody is sure how viruses began. The existence of very large viruses (megaviruses) which contains enough genes to encode about one thousand proteins, more than most bacteria, suggests that they were originally cells which lost the ability to reproduce on their own, adopting instead a parasitic way of life.

However the existence of bacterial spores suggests that perhaps they evolved into viruses.

Viral Diseases

Viruses cause many diseases in plants and animals. For example the human retrovirus HIV causes acquired immune deficiency syndrome (AIDS). Other viruses cause Burkittís lymphoma, chickenpox, the common cold, conjunctivitis, Creutzfeldt-Jakob disease (CJD), encephalitis, enterovirus disease, gastrointestinal infections, glandular fever, hepatitis, herpes simplex, infectious mononucleosis, influenza, kuru, Lassa fever, measles, mumps, polio, rabies, respiratory infections, rubella (German measles), shingles, smallpox, some cancers, warts and yellow fever. However, viruses also bring some benefits.

Viral Benefits

A virus seems like a totally destructive thing, killing cells without doing any good. Usually this is true, but viruses can carry useful genes from one cell to another. Genetic engineers use viruses for this reason.

Previous pageNext page


History of the Universe eBook. 398 pages, 300 illustrations only $2.99

eBook only $2.99
398 pages, 300 images

"I find the science fabulous...an extremely useful teaching tool."
Professor David Christian

Become a Citizen of the Universe

and get your free badge!