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:9/30/2014)... each year, but its deep-blue waters host the ... alien species, including fish, crustaceans, and algae are ... In the open-access journal Frontiers in Marine ... data from a new information system developed by ... of alien species has changed the native biodiversity ...
(Date:9/30/2014)... have completed the first comprehensive numerical simulation of skeletal ... in an image as data points for the computer ... led by J.S. Chen, the William Prager Professor of ... UC San Diego, presented their findings on the development ... this month. Chen also gave a keynote speech about ...
(Date:9/30/2014)... the Ocean Health Index rates the Earth,s oceans ... In addition, for the first time, the report ... beyond national jurisdiction (high-seas areas) all critical ... and providing sustainable food sources. , In the ... led by scientists from UC Santa Barbara,s National ...
Breaking Biology News(10 mins):Biodiversity in the Mediterranean is threatened by alien species 2First comprehensive meshfree numerical simulation of skeletal muscle tissue achieved 2Rating the planet's oceans 2Rating the planet's oceans 3
... chemistry professor and a neuroscientist working together to test ... biomedical engineer working with an orthopedic surgeon to help ... teamwork is often considered the shortest route toward solving ... can inspire students who are beginning their journey in ...
... most ancient frogs may soon be mined to extinction, if ... area for mining go ahead. The primitive Archey,s frog ... ) are two of the species that inhabit the area ... the mining is planned to take place. Archey,s frog ...
... use of commercial fertilisers and animal waste is contributing ... aquatic environment. Yet global food and bioenergy supplies are ... and Ecology at LIFE Faculty of Life Sciences ... resources at the development of sustainable animal waste technologies. ...
Cached Biology News:HHMI awards $1.2 million to UF for undergrad education 2Prehistoric frogs face extinction 2Massive resources now directed at sustainable animal waste technology 2
Other biology definitionOther Tags