الخميس، 30 أكتوبر 2008

nucleus


Nucleus
The nucleus is found in all eukaryotic cells; this membrane-bound structure contains most of the cell's genetic material (excluded material is primarily the DNA found in mitonchondria). The two primary functions of the nucleus are to control cytoplasmic chemical reactions, and to store information necessary for cell division. The nucleus also contains certain proteins that scientists think regulate the expression of genes.The nucleus of a regular eukaryotic cell varies in diameter from 11 to 22.25 micrometers. It's enclosed in a semiporous double membrane that is variously called the nuclear envelope or the nuclear membrane. The outer membrane is attached to the endoplasmic reticulum. The inside of the nuclear membrane is supported by a structure of filaments or microtubules referred to as the nuclear lamina.Inside the nucleus are one or several nucleoli surrounded by the nucleoplasm made up of dissolved nucleotide triphosphates, enzymes, proteins, and transcription factors, and a network of fibers called the nuclear matrix.The DNA of the cell are found inside the nucleus as well, and RNA are transcribed here.

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