A virus is a biological agent that
reproduces inside the
cells of living
hosts. When infected, a host cell is forced to produce many thousands of identical copies of the original virus, at an extraordinary rate. Unlike most living things, viruses do not have cells that divide; new viruses are assembled in the infected host cell. Over 2,000 species of viruses have been discovered. A virus consists of two or three parts:
genes, made from either
DNA or
RNA, long
molecules that carry the genetic information; a
protein coat that protects the genes; and in some, an
envelope of fat that surrounds and protects them when they are not contained within a host cell. Viruses vary in shape from the simple
helical and
icosahedral to more
complex structures. They spread in many different ways. Whereas viruses such as
influenza are spread through the air by people when they cough or sneeze, others such as
norovirus, which are transmitted by the
faecal–oral route, contaminate hands, food and water.
Rotavirus is often spread by direct contact with infected children. The human immunodeficiency virus,
HIV, is one of several major viruses that are transmitted during sex. Viral infections often cause disease in humans and animals; however, they are usually eliminated by the
immune system, conferring lifetime
immunity to the host for that virus. (
more...)
The red rock crab (Grapsus grapsus) is one of the most common crabs along the western coast of the
Americas. Adults are quite variable in color, including brownish-red, mottled or spotted brown, pink, yellow, bright orange and red. It feeds on
algae primarily, sometimes sampling other plant matter and dead animals.
This Wikipedia is written in
English. Started in 2001 (2001), it currently contains
4,080,071 articles. Many other Wikipedias are available; some of the largest are listed below.
A virus is a biological agent that
reproduces inside the
cells of living
hosts. When infected, a host cell is forced to produce many thousands of identical copies of the original virus, at an extraordinary rate. Unlike most living things, viruses do not have cells that divide; new viruses are assembled in the infected host cell. Over 2,000 species of viruses have been discovered. A virus consists of two or three parts:
genes, made from either
DNA or
RNA, long
molecules that carry the genetic information; a
protein coat that protects the genes; and in some, an
envelope of fat that surrounds and protects them when they are not contained within a host cell. Viruses vary in shape from the simple
helical and
icosahedral to more
complex structures. They spread in many different ways. Whereas viruses such as
influenza are spread through the air by people when they cough or sneeze, others such as
norovirus, which are transmitted by the
faecal–oral route, contaminate hands, food and water.
Rotavirus is often spread by direct contact with infected children. The human immunodeficiency virus,
HIV, is one of several major viruses that are transmitted during sex. Viral infections often cause disease in humans and animals; however, they are usually eliminated by the
immune system, conferring lifetime
immunity to the host for that virus. (
more...)
The red rock crab (Grapsus grapsus) is one of the most common crabs along the western coast of the
Americas. Adults are quite variable in color, including brownish-red, mottled or spotted brown, pink, yellow, bright orange and red. It feeds on
algae primarily, sometimes sampling other plant matter and dead animals.
This Wikipedia is written in
English. Started in 2001 (2001), it currently contains
4,080,071 articles. Many other Wikipedias are available; some of the largest are listed below.