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.

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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)

_____________________ 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)