FACTOID # 25: If you're tired of sitting in traffic on your way to work, move to North Dakota.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
RELATED ARTICLES
People who viewed "Apoptosis" also viewed:
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Apoptosis
A section of mouse liver showing an apoptotic cell indicated by an arrow
A section of mouse liver showing an apoptotic cell indicated by an arrow

Apoptosis (/̩æ.pəpˈto.səs/[1]) is a form of programmed cell death in multicellular organisms. It is one of the main types of programmed cell death (PCD) and involves a series of biochemical events leading to a characteristic cell morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including blebbing, changes to the cell membrane such as loss of membrane asymmetry and attachment, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation (1-4). Processes of disposal of cellular debris whose results do not damage the organism differentiate apoptosis from necrosis. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... Programmed cell death (PCD) is the deliberate suicide of an unwanted cell in a multicellular organism. ... The term morphology in biology refers to the outward appearance (shape, structure, colour, pattern) of an organism or taxon and its component parts. ... The process of apoptosis, with blebbing shown in the middle illustration In cell biology, a bleb is an irregular bulge in the plasma membrane of a cell undergoing apoptosis. ... Look up cell membrane in Wiktionary, the free dictionary. ... Necrosis (in Greek Νεκρός = Dead) is the name given to accidental death of cells and living tissue. ...


In contrast to necrosis, which is a form of traumatic cell death that results from acute cellular injury, apoptosis, in general, confers advantages during an organism's life cycle. For example, the differentiation of fingers and toes in a developing human embryo occurs because cells between the fingers apoptose; the result is that the digits are separate. Between 50 billion and 70 billion cells die each day due to apoptosis in the average human adult. For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day. In a year, this amounts to the proliferation and subsequent destruction of a mass of cells equal to an individual's body weight. Necrosis (in Greek Νεκρός = Dead) is the name given to accidental death of cells and living tissue. ... For other uses, see Embryo (disambiguation). ...


Research on apoptosis has increased substantially since the early 1990s. In addition to its importance as a biological phenomenon, defective apoptotic processes have been implicated in an extensive variety of diseases. Excessive apoptosis causes hypotrophy, such as in ischemic damage, whereas an insufficient amount results in uncontrolled cell proliferation, such as cancer. In medicine, ischemia (Greek ισχαιμία, isch- is restriction, hema or haema is blood) is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ...

Contents

Discovery and etymology

That cell death is a completely normal process in living organisms was already discovered by scientists more than 100 years ago. The German scientist Carl Vogt was first to describe the principle of apoptosis in 1842. In 1885, anatomist Walther Flemming delivered a more precise description of the process of programmed cell death. However, it was not until 1965 that the topic was resurrected. Apoptosis (Greek: apo - from, ptosis - falling; thus etymologically correct pronunciation is æpɒˈtəʊsɪs) was distinguished from traumatic cell death by John Foxton Ross Kerr while he was studying tissues using electron microscopy at the University of Queensland Pathology Department in Brisbane. [2] Following publication of this paper, Kerr was invited to join Professor Alastair R Currie and Andrew Wyllie, Currie's PhD student at the time,[3] at the University of Aberdeen to continue his research. In 1972, the trio published a seminal article in the British Journal of Cancer.[4] Kerr had originally used the term "programmed cell necrosis" to describe the phenomenon but in the 1972 article this process of natural cell death was called apoptosis. Kerr, Wylie and Currie credited Professor James Cormack (Department of Greek, University of Aberdeen) with suggesting the term apoptosis. In Greek, apoptosis means "dropping off" of petals or leaves from plants or trees. Cormack reintroduced the term for medical use as it had a medical meaning for the Greeks over two thousand years before. Hippocrates used the term to mean "the falling off of the bones". Galen extended its meaning to "the dropping of the scabs". Cormack was no doubt aware of this usage when he suggested the name. Debate continues over the correct pronunciation, with opinion divided between a pronunciation with a silent P (pronounced /æpɒˈtəʊsɪs/), and the P spelt out (pronounced /æpɒpˈtəʊsɪs/),[5][6] but the Greek root has a silent P, like pterodactyl. Silent P's from Greek roots typically become voiced when they are used in combining forms preceded by a vowel, as in helicopter or the orders of insects: diptera, lepidoptera, etc. Apoptosis is the process of programmed cell death. ... Karl Christoph Vogt (July 5, 1817 – May 5, 1895) was a German scientist moved to Switzerland. ... Illustrations of cells with chromosomes and mitosis, from the book Zell-substanz, Kern und Zelltheilung, 1882 Walther Flemming (born April 21, 1843 in Sachsenberg, Germany; died August 4, 1905 in Kiel) was a founder of the study of cytogenetics. ... The electron microscope is a microscope that can magnify very small details with high resolving power due to the use of electrons rather than light to scatter off material, magnifying at levels up to 500,000 times. ... The University of Queensland (UQ) is the longest-established university in the state of Queensland, Australia, a member of Australias Group of Eight, and the Sandstone Universities. ... For other uses, see Brisbane (disambiguation). ... PhD usually refers to the academic title Doctor of Philosophy PhD can also refer to the manga Phantasy Degree This is a disambiguation page — a list of pages that otherwise might share the same title. ... The British Journal of Cancer a twice-monthly professional medical journal of Cancer Research UK (a registered charity in the United Kingdom), published on their behalf by the Nature Publishing Group (a division of Macmillan Publishers Ltd). ... The University of Aberdeen was founded in 1495, in Aberdeen, Scotland. ... For other uses, see Hippocrates (disambiguation). ... For other uses, see Galen (disambiguation). ... This article or section does not cite its references or sources. ... For other uses, see Helicopter (disambiguation). ...


John Foxton Ross Kerr, Emeritus Professor of Pathology at the University of Queensland, received the Paul Ehrlich and Ludwig Darmstaedter Prize on March 14, 2000, for his description of apoptosis. He shared the prize with Boston biologist Robert Horvitz.[7] A renal cell carcinoma (chromophobe type) viewed on a hematoxylin & eosin stained slide Pathologist redirects here. ... The University of Queensland (UQ) is the longest-established university in the state of Queensland, Australia, a member of Australias Group of Eight, and the Sandstone Universities. ... is the 73rd day of the year (74th in leap years) in the Gregorian calendar. ... Year 2000 (MM) was a leap year starting on Saturday. ... H. Robert Horvitz is an American biologist best known for his research on the nematode worm Caenorhabditis elegans. ...


Functions

Cell termination

Apoptosis can occur when a cell is damaged beyond repair, infected with a virus, or undergoing stress conditions such as starvation. DNA damage from ionizing radiation or toxic chemicals can also induce apoptosis via the actions of the tumour-suppressing gene p53. The "decision" for apoptosis can come from the cell itself, from the surrounding tissue, or from a cell that is part of the immune system. In these cases apoptosis functions to remove the damaged cell, preventing it from sapping further nutrients from the organism, or to prevent the spread of viral infection. A common alternate meaning of virus is computer virus. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Radiation hazard symbol. ... TP53 bound to a short DNA fragment. ... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ...


Apoptosis also plays a role in preventing cancer; if a cell is unable to undergo apoptosis, due to mutation or biochemical inhibition, it can continue dividing and develop into a tumour. For example, infection by papillomaviruses causes a viral gene to interfere with the cell's p53 protein, an important member of the apoptotic pathway. This interference in the apoptotic capability of the cell plays a critical role in the development of cervical cancer. Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... For linguistic mutation, see Apophony. ... Tumor (American English) or tumour (British English) originally means swelling, and is sometimes still used with that meaning. ... Species See text Papillomaviruses are viruses that commonly cause warts. ... Cervical cancer is a malignant cancer of the cervix. ...


Homeostasis

In the adult organism, the number of cells is kept relatively constant through cell death and division. Cells must be replaced when they become diseased or malfunctioning; but proliferation must be compensated by cell death.[8] This balancing process is part of the homeostasis required by living organisms to maintain their internal states within certain limits. Some scientists have suggested homeodynamics as a more accurate term.[9] The related term allostasis reflects a balance of a more complex nature by the body. Homeostasis (from Greek: ὅμος, homos, equal; and ιστημι, histemi, to stand lit. ... Allostasis is the process of achieving stability, or homeostasis, through physiological or behavioral change. ...


Homeostasis is achieved when the rate of mitosis (cell division) in the tissue is balanced by cell death. If this equilibrium is disturbed, one of two potentially fatal disorders occurs: Mitosis divides genetic information during cell division. ...

  • The cells are dividing faster than they die, effectively developing a tumor.
  • The cells are dividing slower than they die, which results in a disorder of cell loss.

The organism must orchestrate a complex series of controls to keep homeostasis tightly controlled, a process that is ongoing for the life of the organism and involves many different types of cell signaling. Impairment of any one of these controls can lead to a diseased state; for example, dysregulation of signaling pathway has been implicated in several forms of cancer. The pathway, which conveys an anti-apoptotic signal, has been found to be activated in pancreatic adenocarcinoma tissues. For malignant tumors specifically, see cancer. ... Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. ... The pancreas is a gland organ in the digestive and endocrine systems of vertebrates. ... Adenocarcinoma is a form of carcinoma that originates in glandular tissue. ...


Development

Incomplete differentiation in two toes (syndactyly) due to lack of apoptosis
Incomplete differentiation in two toes (syndactyly) due to lack of apoptosis

Programmed cell death is an integral part of both plant and animal tissue development. Development of an organ or tissue is often preceded by the extensive division and differentiation of a particular cell, the resultant mass is then "pruned" into the correct form by apoptosis. Unlike cellular death caused by injury, apoptosis results in cell shrinkage and fragmentation. This allows the cells to be efficiently phagocytosed and their components reused without releasing potentially harmful intracellular substances (such as hydrolytic enzymes, for example) into the surrounding tissue. Image File history File links Download high-resolution version (2272x1662, 565 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Apoptosis Dactyly Webbed toes ... Image File history File links Download high-resolution version (2272x1662, 565 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Apoptosis Dactyly Webbed toes ... In zoology, dactyly is the arrangement of digits (fingers and toes) on the hands, feet, or sometimes wings of an animal. ... Biological tissue is a collection of interconnected cells that perform a similar function within an organism. ... Views of a Foetus in the Womb, Leonardo da Vinci, ca. ... In phagocytosis (literally, cell eating), large particles are enveloped by the cell membrane of a (usually larger) cell and internalized to form a food vacuole. ...


Research on chick embryos has suggested how selective cell proliferation, combined with selective apoptosis, sculpts developing tissues in vertebrates. During vertebrate embryo development, structures called the notochord and the floor plate secrete a gradient of the signaling molecule (Shh), and it is this gradient that directs cells to form patterns in the embryonic neural tube: cells that receive Shh in a receptor in their membranes called Patched1 (Ptc1) survive and proliferate; but, in the absence of Shh, one of the ends of this same Ptc1 receptor (the carboxyl-terminal, inside the membrane) is cleaved by caspase-3, an action that exposes an apoptosis-producing domain.[10][11] The notochord is a flexible, rod-shaped body found in embryos of all chordates. ... For the video game character, see Sonic the Hedgehog. ...


During development, apoptosis is tightly regulated and different tissues use different signals for inducing apoptosis. In birds, bone morphogenetic proteins (BMP) signaling is used to induce apoptosis in the interdigital tissue. In Drosophila flies, steroid hormones regulate cell death. Developmental cues can also induce apoptosis, such as the sex-specific cell death of hermaphrodite specific neurons in C. elegans males through low TRA-1 transcription factor activity (TRA-1 helps prevent cell death). Bone morphogenetic proteins (BMPs) are growth factors belonging to the TGF-β (Transforming Growth Factor-beta) super family with a strong ability to induce new bone and/or cartilage formation. ... Type species Drosophila funebris (Fabricius, 1787) Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called fruit flies, or more appropriately vinegar flies, wine flies, pomace flies, grape flies, and picked fruit-flies, a reference to the characteristic of many species to linger... Steroid hormones are steroids which act as hormones. ... For other uses, see Hermaphrodite (disambiguation). ... Neurons (also called nerve cells) are the primary cells of the nervous system. ... Binomial name Caenorhabditis elegans Wild-type C. elegans hermaphrodite stained to highlight the nuclei of all cells Caenorhabditis elegans () is a free-living nematode (a roundworm), about 1 mm in length, which lives in a temperate soil environment. ...


Lymphocyte interactions

The development of B lymphocytes and the development of T lymphocytes in the human body is a complex process that effectively creates a large pool of diverse cells to begin with, then weeds out those potentially damaging to the body. Apoptosis is the mechanism by which the body removes both the ineffective and the potentially-damaging immature cells, and in T-cells is initiated by the withdrawal of survival signals.[12] B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response). ... T cells are a subset of lymphocytes that play a large role in the immune response. ...


Cytotoxic T-cells are able to directly induce apoptosis in cells by opening up pores in the target's membrane and releasing chemicals that bypass the normal apoptotic pathway. The pores are created by the action of secreted perforin, and the granules contain granzyme B, a serine protease that activates a variety of caspases by cleaving aspartate residues.[13] A cytotoxic T cell (also known as TC, CTL or killer T cell) belongs to a sub-group of T lymphocytes (a type of white blood cell) which are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses (or other... A cell undergoing apoptosis. ... Perforin is a cytolytic protein found in the granules of CD8 T-cells and NK cells. ... Granzymes are exogenous serine proteases that are released by cytoplasmic granules within cytotoxic T cells and natural killer cells. ... Crystal structure of Trypsin, a typical serine protease. ... Aspartic acid, also known as aspartate, the name of its anion, is one of the 20 natural proteinogenic amino acids which are the building blocks of proteins. ...


Process

The process of apoptosis is controlled by a diverse range of cell signals, which may originate either extracellularly (extrinsic inducers) or intracellularly (intrinsic inducers). Extracellular signals may include hormones, growth factors, nitric oxide[14] or cytokines, and therefore must either cross the plasma membrane or transduce to effect a response. These signals may positively or negatively induce apoptosis; in this context the binding and subsequent initiation of apoptosis by a molecule is termed positive, whereas the active repression of apoptosis by a molecule is termed negative. Image File history File links No higher resolution available. ... It has been suggested that this article or section be merged into signal transduction. ... For other uses, see Hormone (disambiguation). ... Growth factor is a protein that acts as a signaling molecule between cells (like cytokines and hormones) that attaches to specific receptors on the surface of a target cell and promotes differentiation and maturation of these cells. ... R-phrases , , , , S-phrases , , , Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Nitric oxide or Nitrogen monoxide is a chemical compound with chemical formula NO. This gas is an important signaling molecule in the body of... Cytokines are a category of less-widely-known signalling proteins and glycoproteins that, like hormones and neurotransmitters, are used extensively in cellular communication. ... In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another, most often involving ordered sequences of biochemical reactions inside the cell, that are carried out by enzymes and linked through second messengers resulting in what is thought of as...


Intracellular apoptotic signalling is a response initiated by a cell in response to stress, and may ultimately result in cell suicide. The binding of nuclear receptors by glucocorticoids, heat, radiation, nutrient deprivation, viral infection, and hypoxia are all factors that can lead to the release of intracellular apoptotic signals by a damaged cell.[13] A number of cellular components, such as poly ADP ribose polymerase, may also help regulate apoptosis.[15] Glucocorticoids are a class of steroid hormones characterised by an ability to bind with the cortisol receptor and trigger similar effects. ... Hypoxia is a pathological condition in which the body as a whole (generalised hypoxia) or region of the body (tissue hypoxia) is deprived of adequate oxygen supply. ... Poly (ADP-ribose) polymerase (PARP) is a protein involved in a number of cellular processes involving mainly DNA repair and programmed cell death. ...


Before the actual process of cell death is carried out by enzymes, apoptotic signals must be connected to the actual death pathway by way of regulatory proteins. This step allows apoptotic signals to either culminate in cell death, or be aborted should the cell no longer need to die. Several proteins are involved, however two main methods of achieving regulation have been identified; targeting mitochondria functionality, or directly transducing the signal via adapter proteins to the apoptotic mechanisms. The whole preparation process requires energy and functioning cell machinery. In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ...


Mitochondrial regulation

The mitochondria are essential to multicellular life. Without them, a cell ceases to respire aerobically and quickly dies - a fact exploited by some apoptotic pathways. Apoptotic proteins that target mitochondria affect them in different ways; they may cause mitochondrial swelling through the formation of membrane pores, or they may increase the permeability of the mitochondrial membrane and cause apoptotic effectors to leak out.[13] There is also a growing body of evidence that indicates that nitric oxide (NO) is able to induce apoptosis by helping to dissipate the membrane potential of mitochondria and therefore make it more permeable.[14] This article or section should be merged with aerobic metabolism. ...


Mitochondrial proteins known as SMACs (second mitochondria-derived activator of caspases) are released into the cytosol following an increase in permeability. SMAC binds to inhibitor of apoptosis proteins (IAPs) and deactivates them, preventing the IAPs from arresting the apoptotic process and therefore allowing apoptosis to proceed. IAP also normally suppresses the activity of a group of cysteine proteases called caspases,[16] which carry out the degradation of the cell, therefore the actual degradation enzymes can be seen to be indirectly regulated by mitochondrial permeability. The cytosol (cf. ... Proteases are enzymes that degrade polypeptides. ... Caspases are a group of cysteine proteases, enzymes with a crucial cysteine residue that can cleave other proteins after an aspartic acid residue, a specificity which is unusual among proteases. ...


Cytochrome c is also released from mitochondria due to formation of a channel, MAC, in the outer mitochondrial membrane[17], and serves a regulatory function as it precedes morphological change associated with apoptosis.[13] Once cytochrome c is released it binds with Apaf-1 and ATP, which then bind to pro-caspase-9 to create a protein complex known as an apoptosome. The apoptosome cleaves the pro-caspase to its active form of caspase-9, which in turn activates the effector caspase-3. Cytochrome c with heme c. ... Apaf-1 is a cytosolic protein involved in cell death or apoptosis. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... The apoptosome is a big multi-protein structure formed in the process of apoptosis. ... Caspase-9 is an initiator caspase. ...


MAC is itself subject to regulation by various proteins, such as those encoded by the mammalian Bcl-2 family of anti-apoptopic genes, the homologs of the ced-9 gene found in C. elegans.[18][19] Bcl-2 proteins are able to promote or inhibit apoptosis either by direct action on MAC or indirectly through other proteins. It is important to note that the actions of some Bcl-2 proteins are able to halt apoptosis even if cytochrome c has been released by the mitochondria.[13] B cell lymphoma (Bcl)-2 is a mammalian protein family whose members govern mitochondrial membrane permeabilisation (MMP), a key event in apoptosis. ... Binomial name Caenorhabditis elegans Wild-type C. elegans hermaphrodite stained to highlight the nuclei of all cells Caenorhabditis elegans () is a free-living nematode (a roundworm), about 1 mm in length, which lives in a temperate soil environment. ...


Direct signal transduction

Overview of TNF signalling in apoptosis, an example of direct signal transduction
Overview of TNF signalling in apoptosis, an example of direct signal transduction
Overview of Fas signalling in apoptosis, an example of direct signal transduction
Overview of Fas signalling in apoptosis, an example of direct signal transduction

Two important examples of the direct initiation of apoptotic mechanisms in mammals include the TNF-induced (tumour necrosis factor) model and the Fas-Fas ligand-mediated model, both involving receptors of the TNF receptor (TNFR) family[20] coupled to extrinsic signals. Image File history File links TFN-signalling. ... Image File history File links TFN-signalling. ... Image File history File links Fas-signalling. ... Image File history File links Fas-signalling. ... In medicine, tumor necrosis factor alpha (TNFα, cachexin or cachectin) is an important cytokine involved in systemic inflammation and the acute phase response. ... In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as a...


TNF is a cytokine produced mainly by activated macrophages, and is the major extrinsic mediator of apoptosis. Most cells in the human body have two receptors for TNF: TNF-R1 and TNF-R2. The binding of TNF to TNF-R1 has been shown to initiate the pathway that leads to caspase activation via the intermediate membrane proteins TNF receptor-associated death domain (TRADD) and Fas-associated death domain protein (FADD).[21] Binding of this receptor can also indirectly lead to the activation of transcription factors involved in cell survival and inflammatory responses.[22] The link between TNF and apoptosis shows why an abnormal production of TNF plays a fundamental role in several human diseases, especially in autoimmune diseases. Cytokines are a category of less-widely-known signalling proteins and glycoproteins that, like hormones and neurotransmitters, are used extensively in cellular communication. ... A macrophage of a mouse stretching its arms to engulf two particles, possibly pathogens Macrophages (Greek: big eaters, from makros large + phagein eat) are cells within the tissues that originate from specific white blood cells called monocytes. ... In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. ... Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. ...


The Fas receptor (also known as Apo-1 or CD95) binds the Fas ligand (FasL), a transmembrane protein part of the TNF family.[20] The interaction between Fas and FasL results in the formation of the death-inducing signaling complex (DISC), which contains the FADD, caspase-8 and caspase-10. In some types of cells (type I), processed caspase-8 directly activates other members of the caspase family, and triggers the execution of apoptosis. In other types of cells (type II), the Fas-DISC starts a feedback loop that spirals into increasing release of pro-apoptotic factors from mitochondria and the amplified activation of caspase-8.[23] The Fas receptor (FasR) is the most intensely studied member of the death receptor family. ... The FAS ligand or FasL is a type II transmembrane protein that belongs to the tumor necrosis factor (TNF) family. ... A transmembrane protein is a protein that spans the entire biological membrane. ...


Following TNF-R1 and Fas activation in mammalian cells a balance between pro-apoptotic (BAX,[24] BID, BAK, or BAD) and anti-apoptotic (Bcl-Xl and Bcl-2) members of the Bcl-2 family is established. This balance is the proportion of pro-apoptotic homodimers that form in the outer-membrane of the mitochondrion. The pro-apoptotic homodimers are required to make the mitochondrial membrane permeable for the release of caspase activators such as cytochrome c and SMAC. Control of pro-apoptotic proteins under normal cell conditions of non-apoptotic cells is incompletely understood, but it has been found that a mitochondrial outer-membrane protein, VDAC2, interacts with BAK to keep this potentially-lethal apoptotic effector under control.[25] When the death signal is received, products of the activation cascade displace VDAC2 and BAK is able to be activated. The Bcl-2–associated X protein, or BAX, gene was the first identified pro-apoptotic member of the Bcl-2 protein family. ... The BH3 interacting domain death agonist, or BID, gene is a pro-apoptotic member of the Bcl-2 protein family. ... The Bcl-2 homologous antagonist/killer (BAK) protein is a pro-apoptotic member of the Bcl-2 gene family which is involved in initiating apoptosis. ... The Bcl-2-associated death promoter (BAD) protein is a pro-apoptotic member of the Bcl-2 gene family which is involved in initiating apoptosis. ... Sucrose, or common table sugar, is composed of glucose and fructose. ...


There also exists a caspase-independent apoptotic pathway that is mediated by AIF (apoptosis-inducing factor). For more information, see the article of the author Susin in Nature of 1999 and also reference 21 mentioned below.


Execution

Although many pathways and signals lead to apoptosis, there is only one mechanism that actually causes the death of the cell in this process; after the appropriate stimulus has been received by the cell and the necessary controls exerted, a cell will undergo the organized degradation of cellular organelles by activated proteolytic caspases. A cell undergoing apoptosis shows a characteristic morphology that can be observed with a microscope: Proteolysis is the directed degradation (digestion) of proteins by cellular enzymes called proteases or by intramolecular digestion. ... Caspases are a group of cysteine proteases, enzymes with a crucial cysteine residue that can cleave other proteins after an aspartic acid residue, a specificity which is unusual among proteases. ... A microscope (Greek: (micron) = small + (skopein) = to look at) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. ...

  1. Cell shrinkage and rounding due to the breakdown of the proteinaceous cytoskeleton by caspases.
  2. The cytoplasm appears dense, and the organelles appear tightly packed.
  3. Chromatin undergoes condensation into compact patches against the nuclear envelope in a process known as pyknosis, a hallmark of apoptosis.[26][27]
  4. The nuclear envelope becomes discontinuous and the DNA inside it is fragmented in a process referred to as karyorrhexis. The nucleus breaks into several discrete chromatin bodies or nucleosomal units due to the degradation of DNA.[28]
  5. The cell membrane shows irregular buds known as blebs.
  6. The cell breaks apart into several vesicles called apoptotic bodies, which are then phagocytosed.

Apoptosis progresses quickly and its products are quickly removed, making it difficult to detect or visualize. During karyorrhexis, endonuclease activation leaves short DNA fragments, regularly spaced in size. These give a characteristic "laddered" appearance on agar gel after electrophoresis. Tests for DNA laddering differentiate apoptosis from ischemic or toxic cell death.[29] The nuclear envelope (also known as the perinuclear envelope, nuclear membrane, nucleolemma or karyotheca) is the double membrane of the nucleus that encloses genetic material in eukaryotic cells. ... Pyknosis, or karyopyknosis, is the condensation of chromatin in the nucleus of a cell undergoing programmed cell death (see Naoufal Zamzami and Guido Kroemer: Apoptosis: Condensed matter in cell death, Nature Vol. ... Karyorrhexis is the fragmentation of the nucleus of a cell undergoing programmed cell death (see Naoufal Zamzami and Guido Kroemer: Apoptosis: Condensed matter in cell death, Nature Vol. ... The process of apoptosis, with blebbing shown in the middle illustration In cell biology, a bleb is an irregular bulge in the plasma membrane of a cell undergoing apoptosis. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... Endonucleases are enzymes that cleave the phosphodiester bond within a nucleotide chain. ... This does not adequately cite its references or sources. ... For specific types of electrophoresis (for example, the process of administering medicine, iontophoresis), see electrophoresis (disambiguation). ... DNA laddering is a phenomenon seen in laboratory tests; it is a sensitive indicator of programmed cell death, specifically of apoptosis. ... In medicine, ischemia (Greek ισχαιμία, isch- is restriction, hema or haema is blood) is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. ...


Removal of dead cells

Dying cells that undergo the final stages of apoptosis display phagocytotic molecules, such as phosphatidylserine, on their cell surface.[30] Phosphatidylserine is normally found on the cytosolic surface of the plasma membrane, but is redistributed during apoptosis to the extracellular surface by a hypothetical protein known as scramblase.[31] These molecules mark the cell for phagocytosis by cells possessing the appropriate receptors, such as macrophages.[32] Upon recognition, the phagocyte reorganizes its cytoskeleton for engulfment of the cell. The removal of dying cells by phagocytes occurs in an orderly manner without eliciting an inflammatory response. Phosphatidylserine is a phospholipid nutrient found in fish, green leafy vegetables, soybeans and rice, and is essential for the normal functioning of neuronal cell membranes. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Steps of a macrophage ingesting a pathogen: a. ... woooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooot! - Howard Dean ...


Implication in disease

A section of mouse liver showing several apoptotic cells, indicated by arrows
A section of mouse liver showing several apoptotic cells, indicated by arrows
A section of mouse liver stained to show cells undergoing apoptosis (orange)
A section of mouse liver stained to show cells undergoing apoptosis (orange)

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Staining is a biochemical technique of adding a class-specific (DNA, proteins, lipids, carbohydrates) dye to a substrate to qualify or quantify the presence of a specific compound. ...

Defective apoptotic pathways

The many different types of apoptotic pathways contain a multitude of different biochemical components, many of them not yet understood.[8] As a pathway is more or less sequential in nature it is a victim of causality; removing or modifying one component leads to an effect in another. In a living organism this can have disastrous effects, often in the form of disease or disorder. A discussion of every disease caused by modification of the various apoptotic pathways would be impractical, but the concept overlying each one is the same: the normal functioning of the pathway has been disrupted in such a way as to impair the ability of the cell to undergo normal apoptosis. This results in a cell that lives past its "use-by-date" and is able to replicate and pass on any faulty machinery to its progeny, increasing the likelihood of the cell becoming cancerous or diseased.


A recently-described example of this concept in action can be seen in the development of a lung cancer called NCI-H460.[33] The X-linked inhibitor of apoptosis protein (XIAP) is overexpressed in cells of the H460 cell line. XIAPs bind to the processed form of caspase-9, and suppress the activity of apoptotic activator cytochrome c, therefore overexpression leads to a decrease in the amount of pro-apoptotic agonists. As a consequence, the balance of anti-apoptotic and pro-apoptotic effectors is upset in favour of the former, and the damaged cells continue to replicate despite being directed to die. X-linked Inhibitor of Apoptosis Protein (XIAP) is a member of the Inhibitor of apoptosis family of proteins (IAP). ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the... Epithelial cells in culture, stained for keratin (red) and DNA (green) Cell culture is the term applied when growing cells in a synthetic environment. ... Cytochrome c with heme c. ...


p53 disregulation

The tumor-suppressor protein p53 accumulates when DNA is damaged due to a chain of biochemical reactions. Part of this pathway includes interferon-alpha and interferon-beta, which induce transcription of the p53 gene and result in the increase of p53 protein level and enhancement of cancer cell-apoptosis.[34] p53 prevents the cell from replicating by stopping the cell cycle at G1, or interphase, to give the cell time to repair, however it will induce apoptosis if damage is extensive and repair efforts fail. Any disruption to the regulation of the p53 or interferon genes will result in impaired apoptosis and the possible formation of tumors. TP53 bound to a short DNA fragment. ... Interferons (IFNs) are natural proteins produced by the cells of the immune system of most vertebrates in response to challenges by foreign agents such as viruses, bacteria, parasites and tumor cells. ... The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell leading to its replication. ...


HIV progression

The progression of the human immunodeficiency virus (HIV) to AIDS is primarily due to the depletion of CD4+ T-helper lymphocytes, which leads to a compromised immune system. One of the mechanisms by which T-helper cells are depleted is apoptosis, which can be the end-product of multiple biochemical pathways:[35] The human immunodeficiency virus (HIV) is a frequently mutating retrovirus that attacks the human immune system and which has been shown to cause acquired immune deficiency syndrome (AIDS). ... For other uses, see AIDS (disambiguation). ... Antigen presentation stimulates T cells to become either cytotoxic CD8+ cells or helper CD4+ cells. ...

  1. HIV enzymes inactivate anti-apoptotic Bcl-2 and simultaneously activate pro-apoptotic procaspase-8. This does not directly cause cell death but primes the cell for apoptosis should the appropriate signal be received.
  2. HIV products may increase levels of cellular proteins which have a promotive effect on Fas-mediated apoptosis.
  3. HIV proteins decrease the amount of CD4 glycoprotein marker present on the cell membrane.
  4. Released viral particles and proteins present in extracellular fluid are able to induce apoptosis in nearby "bystander" T-helper cells.
  5. HIV decreases the production of molecules involved in marking the cell for apoptosis, giving the virus time to replicate and continue releasing apoptotic agents and virions into the surrounding tissue.
  6. The infected CD4+ cell may also receive the death signal from a cytotoxic T cell, leading to apoptosis.

In addition to apoptosis, infected cells may also die as a direct consequence of the viral infection. CD4 (cluster of differentiation 4) is a molecule that is expressed on the surface of T helper cells (as well as regulatory T cells and dendritic cells). ...


Viral infection

Viruses can trigger apoptosis of infected cells via a range of mechanisms including:

  • Receptor binding.
  • Activation of protein kinase R (PKR).
  • Interaction with p53.
  • Expression of viral proteins coupled to MHC proteins on the surface of the infected cell, allowing recognition by cells of the immune system (such as Natural Killer and cytotoxic T cells) that then induce the infected cell to undergo apoptosis.[36]

Most viruses encode proteins that can inhibit apoptosis.[37] Several viruses encode viral homologs of Bcl-2. These homologs can inhibit pro-apoptotic proteins such as BAX and BAK, which are essential for the activation of apoptosis. Examples of viral Bcl-2 proteins include the Epstein-Barr virus BHRF1 protein and the adenovirus E1B 19K protein.[38] Some viruses express caspase inhibitors that inhibit caspase activity and an example is the CrmA protein of cowpox viruses. Whilst a number of viruses can block the effects of TNF and Fas. For example the M-T2 protein of myxoma viruses can bind TNF preventing it from binding the TNF receptor and inducing a response.[39] Furthermore, many viruses express p53 inhibitors that can bind p53 and inhibit its transcriptional transactivation activity. Consequently p53 cannot induce apoptosis since it cannot induce the expression of pro-apoptotic proteins. The adenovirus E1B-55K protein and the hepatitis B virus HBx protein are examples of viral proteins that can perform such a function.[40] Protein kinase R (PKR) is activated by double-stranded RNA (dsRNA) and plays a major role in the cellular response to viral infection. ... The Epstein-Barr virus (EBV), also called Human herpesvirus 4 (HHV-4), is a virus of the herpes family (which includes Herpes simplex virus and Cytomegalovirus), and is one of the most common viruses in humans. ... Genera Mastadenovirus Aviadenovirus Atadenovirus Siadenovirus Adenoviruses are viruses of the family Adenoviridae. ... HBV redirects here. ...


Interestingly, viruses can remain intact from apoptosis particularly in the latter stages of infection. They can be exported in the apoptotic bodies that pinch off from the surface of the dying cell and the fact that they are engulfed by phagocytes prevents the initiation of a host response. This favours the spread of the virus.[39]


See also

Anoikis (Greek: homelessness) is a form of apoptosis which is induced by anchorage-dependent cells detaching from the surrounding extracellular matrix (ECM)[1]. Usually cells stay close to the tissue which they belong since the communication between proximal cells as well as between cells and ECM provide essential signals for... Apaf-1 is a cytosolic protein involved in cell death or apoptosis. ... Autolysis is the process by which a cell self-destructs (if necessary) for the healthiness of the entire organism. ... Autophagy is also a synonym for self-cannibalism Autophagy, or ocytosis, is a process of sequestering organelles and long-lived proteins in a double-membrane vesicle inside the cell, where the contents are subsequently delivered to the lysosome for degradation. ... The Autophagy network extracted from the recent 500 PubMed entries. ... Necrosis (in Greek Νεκρός = Dead) is the name given to accidental death of cells and living tissue. ... Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. ... A protein confined to the mitochondrial membrane. ...

References

  1. ^ Webster.com dictionary entry
  2. ^ Kerr, JF. (1965). "A histochemical study of hypertrophy and ischaemic injury of rat liver with special reference to changes in lysosomes.". Journal of Pathology and Bacteriology (90): 419-435. 
  3. ^ Agency for Science, Technology and Research. Prof Andrew H. Wyllie - Lecture Abstract. Retrieved on 2007-03-30.
  4. ^ Kerr, JF; Wyllie AH, Currie AR (1972). "Apoptosis: a basic biological phenomenon with wide-ranging implications in tissue kinetics". British Journal of Cancer (26): 239-257. 
  5. ^ Apoptosis Interest Group (1999). About apoptosis. Retrieved on 2006-12-15.
  6. ^ Webster.com dictionary entry
  7. ^ John Kerr and apoptosis The Medical Journal of Australia, 2000; 173: 616-617
  8. ^ a b Thompson, CB (1995). "Apoptosis in the pathogenesis and treatment of disease". Science 267 (5203). 
  9. ^ Damasio, Antonio; (1999). The Feeling of What Happens. New York: Harcourt Brace & Co.. 
  10. ^ Guerrero I, Ruiz i Altaba A. (2003). "Development. Longing for ligand: patched, and cell death". Science 301 (5634). 
  11. ^ Thibert C, Teillet MA, Lapointe F, Mazelin L, Le Douarin NM, Mehlen P. (2003). "Inhibition of neuroepithelial patched-induced apoptosis.". Science 301 (5634). 
  12. ^ Werlen G, et al. (2003). "Signaling life and death in the thymus: timing is everything". Science 299 (5614). 
  13. ^ a b c d e Cotran; Kumar, Collins. Robbins Pathologic Basis of Disease. Philadelphia: W.B Saunders Company. 0-7216-7335-X. 
  14. ^ a b Bernhard Brüne (2003). "Nitric oxide: NO apoptosis or turning it ON?". Nature 10 (8). doi:10.1038/sj.cdd.4401261. 
  15. ^ Chiarugi A, Moskowitz MA (2002). "PARP-1—a perpetrator of apoptotic cell death?". Science 297 (5579). 
  16. ^ Fesik SW, Shi Y. (2001). "Controlling the caspases". Science 294 (5546). 
  17. ^ Laurent M. Dejean, Sonia Martinez-Caballero, Kathleen W. Kinnally (2006). "Is MAC the knife that cuts cytochrome c from mitochondria during apoptosis?". Cell Death and Differentiation 13. doi:10.1038/sj.cdd.4401949. 
  18. ^ Laurent M. Dejean, Sonia Martinez-Caballero, Stephen Manon, Kathleen W. Kinnally (2006). "Regulation of the mitochondrial apoptosis-induced channel, MAC, by BCL-2 family proteins.". Biochim Biophys Acta 1762 (2). 
  19. ^ Lodish, Harvey; et al. (2004). Molecular Cell Biology. New York: W.H. Freedman and Company. 0-7167-4366-3. 
  20. ^ a b Wajant H (2002). "The Fas signaling pathway: more than a paradigm". Science 296 (5573). 
  21. ^ Chen G, Goeddel DV (2002). "TNF-R1 signaling: a beautiful pathway". Science 296 (5573). 
  22. ^ Goeddel, DV et al. "Connection Map for Tumor Necrosis Factor Pathway". Science. doi:[1] 10.1126/stke.3822007tw132]]. 
  23. ^ Wajant, H.. "Connection Map for Fas Signaling Pathway". Science. doi:[2] 10.1126/stke.3802007tr1]]. 
  24. ^ Murphy, KM et al (2000). "Bcl-2 inhibits Bax translocation from cytosol to mitochondria during drug-induced apoptosis of human tumor cells". Cell Death and Differentiation 7 (1). 
  25. ^ Cheng EH (2003). "VDAC2 inhibits BAK activation and mitochondrial apoptosis". Science 301 (5632). 
  26. ^ Santos A. Susin, et al. (2000). "Two Distinct Pathways Leading to Nuclear Apoptosis". Journal of Experimental Medicine 192 (4). doi:10.1073/pnas.191208598v1. 
  27. ^ Madeleine Kihlmark, et al. (2001). "Sequential degradation of proteins from the nuclear envelope during apoptosis". Journal of Cell Science (114). 
  28. ^ Nagata S (2000). "Apoptotic DNA fragmentation". Experimental Cell Research 256 (1). 
  29. ^ M Iwata, D Myerson, B Torok-Storb and RA Zager (1996). An evaluation of renal tubular DNA laddering in response to oxygen deprivation and oxidant injury. Retrieved on 17 April, 2006.
  30. '^ Li MO, et al. (2003). "Phosphatidylserine receptor is required for clearance of apoptotic cells". Science 302 (5650). 
  31. ^ Wang X, et al. (2003). "Cell corpse engulfment mediated by C. elegans phosphatidylserine receptor through CED-5 and CED-12". Science 302 (5650). 
  32. ^ Savill J, Gregory C, Haslett C. (2003). "Eat me or die". Science 302 (5650). 
  33. ^ Yang, L. et al. (2003). "Predominant suppression of apoptosome by inhibitor of apoptosis protein in non-small cell lung cancer H460 cells: therapeutic effect of a novel polyarginine-conjugated Smac peptide.". Cancer Research 63 (4). 
  34. ^ Takaoka A, et al. (2003). "Integration of interferon-alpha/beta signalling to p53 responses in tumour suppression and antiviral defence.". Nature 424 (6948). 
  35. ^ Judie B. Alimonti, T. Blake Ball, Keith R. Fowke (2003). "Mechanisms of CD4+ T lymphocyte cell death in human immunodeficiency virus infection and AIDS". J Gen Virology (84). doi:10.1099/vir.0.19110-0. 
  36. ^ Everett, H. and McFadden, G. (1999). "Apoptosis: an innate immune response to virus infection". Trends Microbiol 7 (4): 160–165. PMID 10217831. 
  37. ^ Teodoro, J.G. Branton, P.E. (1997). "Regulation of apoptosis by viral gene products". J Virol 71 (3): 1739–1746. PMID 9032302. 
  38. ^ Polster, B.M. Pevsner, J. and Hardwick, J.M. (2004). "Viral Bcl-2 homologs and their role in virus replication and associated diseases". Biochim Biophys Acta 1644 (2–3): 211–227. PMID 14996505. 
  39. ^ a b Hay, S. and Kannourakis, G. (2002). "A time to kill: viral manipulation of the cell death program". J Gen Virol 83: 1547–1564. PMID 12075073. 
  40. ^ Wang, X.W. Gibson, M.K. Vermeulen, W. Yeh, H. Forrester, K. Sturzbecher, H.W. Hoeijmakers, J.H. and Harris, C.C. (1995). "Abrogation of p53-induced Apoptosis by the Hepatitis B Virus X Gene". Cancer Res 55 (24): 6012–6016. PMID 8521383. 
  • Alberts, Bruce; et al.. Molecular Biology of the Cell. Garland Publishing. 
  • Bast, Robert C. Jr; et al., (2000). Cancer Medicine, 5th edn. B.C. Decker. 
  • Alfons Lawen (2003). "Apoptosis - an introduction". BioEssays 25 (9). 
  • Α. Afantitis, G. Melagraki, H. Sarimveis, P.A. Koutentis, J. Markopoulos and O. Igglessi – Markopoulou (2006). "A Novel QSAR Model for Modeling and Predicting Induction of Apoptosis by 4-Aryl-4H-chromenes". Bioorganic and Medicinal Chemistry 14. 

Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 89th day of the year (90th in leap years) in the Gregorian calendar. ... The British Journal of Cancer a twice-monthly professional medical journal of Cancer Research UK (a registered charity in the United Kingdom), published on their behalf by the Nature Publishing Group (a division of Macmillan Publishers Ltd). ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 349th day of the year (350th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

External links

is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell leading to its replication. ... Interphase is a phase of the cell cycle. ... The G1 phase is a period in the cell cycle during interphase, after cytokinesis and before the S phase. ... DNA replication. ... G2 phase is a the 3rd and final subphase in interphase of the cell cycle. ... This does not adequately cite its references or sources. ... Mitosis divides genetic information during cell division. ... Newt lung cell in Prophase, with the mitotic spindles stained green and the cell nucleus and chromatin stained blue. ... In early prometaphase, the nuclear membrane has just degraded, allowing the microtubules to quickly interact with the kinetochores on the chromosomes, which have just condensed. ... An image of a newt lung cell stained with fluorescent dyes during metaphase. ... Newt lung cell during late anaphase. ... A cell during telophase that has almost completed cytokinesis. ... A cell that has almost completed cytokinesis. ... Cell cycle checkpoints are control mechanisms that ensure the fidelity of cell division in eukaryotic cells. ... The restriction point is a G1 phase checkpoint in the cell cycle of animal cells. ... // When the genomic DNA of eukaryotic cells becomes damaged by spontaneous processes, chemical mutagens, or sunlight exposure, the replication of damaged DNA triggers a cellular reponse called a postreplication checkpoint [1]. This response prevents cell cycle progression until postreplication repair processes are completed, and may control the activity of these... The G0 phase is a period in the cell cycle where cells exist in a quiescent state. ... Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. ... It has been suggested that this article or section be merged with ligand. ... In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another, most often involving ordered sequences of biochemical reactions inside the cell, that are carried out by enzymes and linked through second messengers resulting in what is thought of as... A section of mouse liver showing an apoptotic cell indicated by an arrow Apoptosis (/̩æ.pÉ™pˈto. ... In cell physiology, a secondary messenger system (also known as a second messenger system) is a method of cellular signalling where the signalling molecule does not enter the cell, but rather utilizes a cascade of events that transduces the signal into a cellular change. ... Calcium ions act as second messengers in signal transduction. ... Lipid signaling refers to a number of cellular signal transduction pathways that use cell membrane lipids as second messengers. ... Paracrine signaling is a form of cell signaling in which the target cell is close to (para = alongside of or next to, but this strict prefix definition is not meticulously followed here) the signal releasing cell. ... Autocrine signaling is a form of signalling in which a cell secretes a chemical messenger (called the autocrine agent) that signals the same cell. ... In biology, juxtacrine signalling is a type of intercellular communication which is transmitted via oligosaccharide, lipid or protein components of a cell membrane and may affect either the emitting cell or immediately adjacent cells. ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ... The endocrine system is an integrated system of small organs that involve the release of extracellular signaling molecules known as hormones. ... redirect Template:Db-reason synaptophysin ... In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ... Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cells plasma membrane, but also in the membranes of some subcellular compartments and organelles. ... Intracellular receptors or nuclear receptors are a class of receptor located inside the cell rather than on its cell membrane. ... In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. ... General transcription factors (GTFs) are proteins which have been shown to be important in the transcription of class II genes to mRNA templates. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Transcription Factor II D (TFIID) is one of several basal transcription factors, all which are involved in the assembly of the basal apparatus of RNA polymerase II. TFIID is itself composed of several subunits called TAFs (of which there are 14) and the TATA Binding Protein (TBP) of which only... TFIIH is a general transcription factor which includes ERCC2 and XPB. MeSH Transcription+Factor+TFIIH      Cell physiology: cell signaling Key concepts: Ligand - Receptor (Transmembrane, Intracellular) - Transcription factor (General, Preinitiation complex, TFIID, TFIIH) - Cell signaling networks - Signal transduction - Adaptor protein - Apoptosis - Second messenger system (Ca2+ signaling, Lipid signaling) Paracrine - Autocrine - Juxtacrine... An adaptor protein is a protein which is accessory to main proteins in signal transduction. ... It has been suggested that this article or section be merged with ligand. ... Hormone is also the NATO reporting name for the Soviet/Russian Kamov Ka-25 military helicopter. ... Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a presynaptic and a postsynaptic neuron. ... Cytokines are small protein molecules that are the core of communication between immune system cells, and even between immune system cells and cells belonging to other tissue types. ... Growth factor is any of about twenty small proteins that attach to specific receptors on the surface of stem cells in bone marrow and promote differentiation and maturation of these cells into morphotic constituents of blood. ...

  Results from FactBites:
 
Apoptosis - Wikipedia, the free encyclopedia (4380 words)
In just one of many scenarios of apoptosis, the process is triggered by another neighboring cell; the dying cell eventually transmits signals that tell the phagocytes, which are a part of the immune system, to engulf it.
Apoptosis can occur, for instance, when a cell is damaged beyond repair, or infected with a virus.
Abnormal apoptosis and clearance of apoptotic cells is a fundamental factor in the pathogenesis of numerous diseases including cancer, neuro-degenerative and ischemic diseases, AIDS, and autoimmunity.
A Brief Introduction to Apoptosis (1115 words)
Morphologically, apoptosis is characterized by a series of structural changes in dying cells: blebbing of the plasma membrane, condensation of the cytoplasm and nucleus, and cellular fragmentation into membrane apoptotic bodies (Steller, 1995; Wyllie et al.
Although apoptosis is important for the normal development and health of an animal, its aberrant activation may contribute to a number of diseases, for example, AIDS, neurogenerative disorders, and ischemic injury (Thompson, 1995).
In contrast, impaired apoptosis may be a significant factor in the etiology of such diseases as cancer, autoimmune disorders, and viral infections (Thompson, 1995).
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m