Navigation Links
Cell nucleus

In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is an organelle, found in the majority of eukaryotic cells, which contains most of the cell's genetic material. Nuclei have two primary functions: to control chemical reactions within the cytoplasm and to store information needed for cellular division.

The nucleus, being the largest organelle, varies in diameter from 10 to 20 micrometres. It is enclosed by a double membrane called the nuclear envelope. The inner and outer membrane fuse at regular intervals, forming nuclear pores. The nuclear envelope regulates and facilitates transport between the nucleus and the cytoplasm, while separating the chemical reactions taking place in cytoplasm from reactions happening within the nucleus. The outer membrane is continuous with the rough endoplasmic reticulum (RER) and may be studded with ribosomes. The space between the two membranes (called the "perinuclear space") is continuous with the lumen of the RER.

Drawing of nucleus and the endoplasmic reticulum.
(1) Nuclear envelope. (2) Ribosomes. (3) Nuclear pore complexes. (4) Nucleolus.
(5) Chromatin. (6) Nucleus. (7) Endoplasmic reticulum. (8) Nucleoplasm.
The whole structure is surrounded by cytoplasm. (Drawing is based on ER images.)

Inside the nucleus is one or several nucleoli surrounded by a fibrous matrix called the nucleoplasm. The nucleoplasm is a liquid with a gel-like consistency (similar in this respect to the cytoplasm), in which many substances are dissolved. These substances include nucleotide triphospates, enzymes, proteins, and transcription factors. Genetic material (DNA) is also present in the nucleus, the DNA is present as a DNA-protein complex called chromatin. The DNA is present as a number of discrete units known as chromosomes.

There are two types of chromatin: euchromatin and heterochromatin. Euchromatin is the least compact form of DNA, and the regions of DNA which constitute euchromatin contain genes which are frequently expressed by the cell.

In heterochromatin, DNA is more tightly compacted. Regions of DNA which constitute heterochromatin generally contain genes which are not expressed by the cell (this type of heterochromatin is known as facultative heterochromatin) or are regions which make up the telomeres and centromeres of the chromosomes (this type of heterochromatin is known as constitutive heterochromatin). In multicellular organisms, cells are highly specialised to perform particular functions, hence different sets of genes are required and expressed. Therefore, the regions of DNA that constitute heterochromatin vary between cell types.

Nucleoli are densely-stained structures at which ribosome subunits are assembled.


(Date:10/14/2014)... led by researchers at the University of Massachusetts ... Miller School of Medicine (UMMSM) have identified what ... (manic depressive) disorder, a breakthrough that could lead ... as well as depression and other related mood ... week in Nature Molecular Psychiatry , show ...
(Date:10/14/2014)... takes between 10 and 20 years to develop, ... of intervention if detected early, which may be ... Australian clinical researchers. , Dr Jeremy Humphris ... of Medical Research, analysed medical histories and tumour ... cancer patients, operated on between 1994 and 20122. ...
(Date:10/14/2014)... Stanford University School of Medicine have discovered a link ... activation of muscle stem cells. Cells use autophagy to ... of nutrient deprivation. The scientists report in The ... operational it also seems to assist in the activation ... cells emerge from a quiescent state there is a ...
Breaking Biology News(10 mins):Rare genetic disease protects against bipolar disorder 2Rare genetic disease protects against bipolar disorder 3Early detection window when pancreatic cancer is in the family 2Autophagy helps fast track stem cell activation 2
... Weiblen and colleagues have found a faster way to ... Using a technique called DNA barcoding, which involves the ... and an international team of researchers studied populations of ... DNA barcodes showed that migratory patterns and caterpillar diets ...
... The humble papaya is gaining credibility in Western ... for generations. University of Florida researcher Nam Dang, ... dramatic anticancer effect against a broad range of lab-grown ... and pancreas. The researchers used an extract made from ...
... Subhash Khot, an associate professor at the Courant Institute ... 2010 Alan T. Waterman Award, which is given annually ... science and engineering supported by NSF. The honor includes ... research or advanced study in any field of science. ...
Cached Biology News:Papaya extract thwarts growth of cancer cells in lab tests 2NYU Courant professor wins NSF's Waterman Award 2
Other biology definitionOther Tags