The cell nucleus is a membrane-enclosed organelle found in most
eukaryotic cells. It contains most of the cell's genetic material,
organized as multiple long linear DNA molecules in complex with a
large variety of proteins such as histones to form chromosomes. The
genes within these chromosomes make up the cell's nuclear genome. The
function of the nucleus is to maintain the integrity of these genes
and to control the activities of the cell by regulating gene
expression. The main structural elements of the nucleus are the
nuclear envelope, a double membrane that encloses the entire organelle
and keeps its contents separated from the cellular cytoplasm, and the
nuclear lamina, a meshwork within the nucleus that adds mechanical
support much like the cytoskeleton supports the cell as a whole.
Because the nuclear membrane is impermeable to most molecules, nuclear
pores are required to allow movement of molecules across the envelope.
Although the interior of the nucleus does not contain any
membrane-delineated bodies, its contents are not uniform, and a number
of subnuclear bodies exist, made up of unique proteins, RNA molecules,
and DNA conglomerates. The best known of these is the nucleolus, which
is mainly involved in assembly of ribosomes. After being produced in
the nucleolus, ribosomes are exported to the cytoplasm where they
translate mRNA. The nucleus was the first organelle to be discovered,
and was first described by Franz Bauer in 1802. It was later described
in more detail by Scottish botanist Robert Brown in 1831.
Read the rest of this article:
http://en.wikipedia.org/wiki/Cell_nucleus
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Today's selected anniversaries:
1264:
King Henry III was captured in the Battle of Lewes, making Simon de
Montfort the de facto ruler of England.
(
http://en.wikipedia.org/wiki/Henry_III_of_England)
1607:
An expedition led by Christopher Newport established the Jamestown
Settlement in Virginia, the first permanent English settlement in
North America.
(
http://en.wikipedia.org/wiki/Jamestown_Settlement)
1796:
Edward Jenner began testing cowpox as a vaccine for protection against
smallpox.
(
http://en.wikipedia.org/wiki/Edward_Jenner)
1948:
Prime Minister David Ben-Gurion publicly read the Declaration of
Independence in Tel Aviv.
(
http://en.wikipedia.org/wiki/Declaration_of_Independence_(Israel))
1973:
The NASA space station Skylab was launched from Cape Canaveral.
(
http://en.wikipedia.org/wiki/Skylab)
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Wikiquote of the day:
I would like to be remembered as a man who had a wonderful time living
his life, and who had good friends, a fine family. I don't think I
could ask for anything more than that, actually. -- Frank Sinatra
(
http://en.wikiquote.org/wiki/Frank_Sinatra)