In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, meaning kernel) is a membrane-enclosed organelle found in 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 are 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 nucleus is, therefore, the control center of the cell. The main structures making up the nucleus are the nuclear membrane, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm, and the nucleoskeleton (which includes nuclear lamina), a network within the nucleus that adds mechanical support, much like the cytoskeleton, which supports the cell as a whole. Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the maintenance of chromosomes. Because the nuclear membrane is impermeable to large molecules, nuclear pores are required that regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be actively transported by carrier proteins while allowing free movement of small molecules and ions. The interior of the nucleus does not contain any membrane-bound sub compartments, its contents are not uniform, and a number of sub-nuclear bodies exist, made up of unique proteins, RNA molecules, and particular parts of the chromosomes. The best-known of these is the nucleolus, which is mainly involved in the 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. What is most likely the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek (1632 – 1723). He observed a "Lumen", the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still possess nuclei. The nucleus was also described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under microscope when he observed an opaque area, which he called the areola or nucleus, in the cells of the flower's outer layer. He did not suggest a potential function. In 1838, Matthias Schleiden proposed that the nucleus plays a role in generating cells, thus he introduced the name "Cytoblast" (cell builder). He believed that he had observed new cells assembling around "cytoblasts". Franz Meyen was a strong opponent of this view, having already described cells multiplying by division and believing that many cells would have no nuclei. The idea that cells can be generated de novo, by the "cytoblast" or otherwise, contradicted work by Robert Remak (1852) and Rudolf Virchow (1855) who decisively propagated the new paradigm that cells are generated solely by cells ("Omnis cellula e cellula"). The function of the nucleus remained unclear.
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when grains collide). The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations. Thus, the lower size limit for grains in granular material is about 1 µm. On the upper size limit, the physics of granular materials may be applied to ice floes where the individual grains are icebergs and to asteroid belts of the solar system with individual grains being asteroids.
Some examples of granular materials are nuts, coal, sand, rice, coffee, corn flakes, fertilizer and ball bearings. Powders are a special class of granular material due to their small particle size, which makes them more cohesive and more easily suspended in a gas. Granular materials are commercially important in applications as diverse as pharmaceutical industry, agriculture, and energy production. Research into granular materials is thus directly applicable and goes back at least to Charles-Augustin de Coulomb, whose law of friction was originally stated for granular materials.
In pathology, salt-and-pepper chromatin, also salt-and-pepper nuclei and stippled chromatin, refers to cell nuclei that demonstrate granular chromatin (on light microscopy).
Salt-and-pepper chromatin is typically seen in endocrine tumours such as medullary thyroid carcinoma, neuroendocrine tumours and pheochromocytoma.
Endolimax is a genus of amoebozoa that are found in the intestines of various animals, including the species E. nana found in humans. Originally thought to be non-pathogenic, studies suggest it can cause intermittent or chronic diarrhea. Additionally, it is very significant in medicine because it can provide false positives for other tests, notably the similar species Entamoeba histolytica, the pathogen responsible for amoebic dysentery, and because its presence indicates the host has consumed fecal material. It forms cysts with four nuclei which excyst in the body and become trophozoites. Endolimax nana nuclei have a large endosome somewhat off-center and small amounts of visible chromatin or none at all.
Cysts are small, with a spherical to ellipsoidal shape. Mature cysts contain four nuclei; immature cysts are rarely seen. These cysts measure 5-10 um, with a usual range of 6-8 um. In stained preparations, the nucleus has a distinct karysome that, while not as large as that seen in the trophozoite, is still larger than the karysome of the Entamoeba species. Peripheral chromatin is absent. Although the nuclei are not visible in unstained preparations, the karysomes are readily apparent in iodine-stained wet mounts. The cytoplasm may contain diffuse glycogen, and chromatid bodies are absent. Occasionally, small granules or inclusions may occur in the cytoplasm.
Cell biology (formerly cytology, from the Greek kytos, "contain") is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level. Cell biology research encompasses both the great diversity of single-celled organisms like bacteria and protozoa, as well as the many specialized cells in multicellular organisms such as humans, plants, and sponges.
Knowing the components of cells and how cells work is fundamental to all biological sciences. Appreciating the similarities and differences between cell types is particularly important to the fields of cell and molecular biology as well as to biomedical fields such as cancer research and developmental biology. These fundamental similarities and differences provide a unifying theme, sometimes allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types. Therefore, research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology.
In journalism, a human interest story is a feature story that discusses a person or people in an emotional way. It presents people and their problems, concerns, or achievements in a way that brings about interest, sympathy or motivation in the reader or viewer.
Human interest stories may be "the story behind the story" about an event, organization, or otherwise faceless historical happening, such as about the life of an individual soldier during wartime, an interview with a survivor of a natural disaster, a random act of kindness or profile of someone known for a career achievement.