Cilium - wikipedia Cilium This article is about organelles. For fine hairs on insect wings, see Cilium ( entomology ). Not to be confused with Psyllium. Cilium SEM micrograph of the cilia projecting from respiratory epithelium in the lungs Details Identifiers Latin Cilium Code TH H1. 00.01. 1.01014 TH H1. 00.01. 1.01014 Anatomical terminology ( edit on Wikidata ) A cilium ( Latin for eyelash ; the plural is cilia ) is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body. Cilium can measure up to 20 μm and have a diameter around 0.25 μm. There are two types of cilia : motile cilia and nonmotile, or primary cilia, which typically serve as sensory organelles. In eukaryotes, motile cilia and flagella together make up a group of organelles known as undulipodia. Eukaryotic cilia are structurally identical to eukaryotic flagella, although distinctions are sometimes made according to function and / or length. Biologists have various ideas about how the various flagella may have evolved. Contents 1 Types and distribution 1.1 Primary / Immotile cilia 1.2 Motile cilia 2 Structure, assembly, maintenance, and function 2.1 Ciliary rootlet 2.2 Sensing the extracellular environment 3 Cilium - related disease 3.1 Ciliopathy as an origin for many multi-symptom genetic diseases 4 See also 5 References 6 External links Types and distribution Cilia can be divided into primary and motile forms. Primary / immotile cilia In animals, primary cilia are found on nearly every cell. In comparison to motile cilia, non-motile ( or primary ) cilia usually occur one per cell ; nearly all mammalian cells have a single non-motile primary cilium. In addition, examples of specialized primary cilia can be found in human sensory organs such as the eye and the nose : The outer segment of the rod photoreceptor cell in the human eye is connected to its cell body with a specialized non-motile cilium. The dendritic knob of the olfactory neuron, where the odorant receptors are located, also contains non-motile cilia ( about 10 cilia per dendritic knob ). Although the primary cilium was discovered in 1898, it was largely ignored for a century. Only recently has great progress been made in understanding the function of the primary cilium. Until the 1990s, the prevailing view of the primary cilium was that it was merely a vestigial organelle without important function. Recent findings regarding its physiological roles in chemical sensation, signal transduction, and control of cell growth, have led scientists to acknowledge its importance in cell function, with the discovery of its role in diseases not previously recognized to involve the dysgenesis and dysfunction of cilia, such as polycystic kidney disease, congenital heart disease, and an emerging group of genetic ciliopathies. The primary cilium is now known to play an important role in the function of many human organs. The current scientific understanding of primary cilia views them as `` sensory cellular antennae that coordinate a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation. ''. Illustration depicting motile cilia. Motile cilia Larger eukaryotes, such as mammals, have motile cilia as well. Motile cilia are usually present on a cell 's surface in large numbers and beat in coordinated waves. In humans, for example, motile cilia are found in the lining of the trachea ( windpipe ), where they sweep mucus and dirt out of the lungs. In female mammals, the beating of cilia in the Fallopian tubes moves the ovum from the ovary to the uterus. The functioning of motile cilia is strongly dependent on the maintenance of optimal levels of fluid bathing the cilia. Epithelial sodium channels ENaC that are specifically expressed along the entire length of cilia apparently serve as sensors that regulate fluid level surrounding the cilia. Ciliates are microscopic organisms that possess motile cilia exclusively and use them for either locomotion or to simply move liquid over their surface. Structure, assembly, maintenance, and function Eukaryotic motile cilium Inside cilia and flagella is a microtubule - based cytoskeleton called the axoneme. The axoneme of primary cilia typically has a ring of nine outer microtubule doublets ( called a 9 + 0 axoneme ), and the axoneme of a motile cilium has two central microtubule singlets in addition to the nine outer doublets ( called a 9 + 2 axoneme ). The axonemal cytoskeleton acts as a scaffolding for various protein complexes and provides binding sites for molecular motor proteins such as kinesin II, that help carry proteins up and down the microtubules. The dynein in the axoneme forms bridges between neighbouring microtubule doublets. When ATP activates the motor domain of dynein, it attempts to walk along the adjoining microtubule doublet. This would force the adjacent doublets to slide over one another if not for the presence of Nexin between the microtubule doublets. And thus the force generated by dyenin is instead converted into a bending motion. Cilia are formed through the process of ciliogenesis. The building blocks of the cilia such as tubulins and other partially assembled axonemal proteins are added to the ciliary tips which point away from the cell body. In most species bi-directional motility called intraflagellar transport ( IFT ) plays an essential role in moving these building materials from the cell body to the assembly site. IFT also carries the disassembled material to be recycled from the ciliary tip back to the cell body. By regulating the equilibrium between these two IFT processes, the length of cilia can be maintained dynamically. Disassembly of cilia requires the action of the Aurora A kinase. Exceptions where IFT is not present include Plasmodium falciparum, which is one of the species of Plasmodium that cause malaria in humans. In this parasite, cilia assemble in the cytoplasm. At the base of the cilium where it attaches to the cell body is the microtubule organizing center, the basal body. Some basal body proteins as CEP164, ODF2 and CEP170, regulate the formation and the stability of the cilium. A transition zone between the basal body and the axoneme `` serves as a docking station for intraflagellar transport and motor proteins. '' In effect, the cilium is a nanomachine composed of perhaps over 600 proteins in molecular complexes, many of which also function independently as nanomachines. Ciliary rootlet The ciliary rootlet is a cytoskeleton - like structure that originates from the basal body at the proximal end of a cilium. It extends proximally toward the cell nucleus. Rootlets are typically 80 - 100 nm in diameter and contain cross striae distributed at regular intervals of approximately 55 - 70 nm. According to the Gene Ontology, the following proteins localize to the ciliary rootlet : amyloid precursor protein, rootletin, kinesins ( KIF5B, KIF5C, KLC2, KLC3 ), and presenilins ( PSEN1, PSEN2 ). Sensing the extracellular environment Some primary cilia on epithelial cells in eukaryotes act as cellular antennae, providing chemosensation, thermosensation and mechanosensation of the extracellular environment. These cilia then play a role in mediating specific signalling cues, including soluble factors in the external cell environment, a secretory role in which a soluble protein is released to have an effect downstream of the fluid flow, and mediation of fluid flow if the cilia are motile. Some epithelial cells are ciliated, and they commonly exist as a sheet of polarized cells forming a tube or tubule with cilia projecting into the lumen. This sensory and signalling role puts cilia in a central role for maintaining the local cellular environment and may be why ciliary defects cause such a wide range of human diseases. Cilium - related disease Main article : Ciliopathy Ciliary defects can lead to a number of human diseases. Genetic mutations compromising the proper functioning of cilia, ciliopathies, can cause chronic disorders such as primary ciliary dyskinesia ( PCD ), nephronophthisis or Senior - Loken syndrome. In addition, a defect of the primary cilium in the renal tube cells can lead to polycystic kidney disease ( PKD ). In another genetic disorder called Bardet - Biedl syndrome ( BBS ), the mutant gene products are the components in the basal body and cilia. Lack of functional cilia in female Fallopian tubes can cause ectopic pregnancy. A fertilized ovum may not reach the uterus if the cilia are unable to move it there. In such a case, the ovum will implant in the Fallopian tubes, causing a tubal pregnancy, the most common form of ectopic pregnancy. As noted above, epithelial sodium channels ENaC that are expressed along the length of cilia regulate fluid level surrounding the cilia. Mutations that decrease the activity of ENaC result in multisystem pseudohypoaldosteronism, that is associated with fertility problems. In cystic fibrosis that results from mutations in the chloride channel CFTR, ENaC activity is enhanced leading to a severe reduction of the fluid level that causes complications and infections in the respiratory airways. Since the flagellum of human sperm is actually a modified cilium, ciliary dysfunction can also be responsible for male infertility. Of interest, there is an association of primary ciliary dyskinesia with left - right anatomic abnormalities such as situs inversus ( a combination of findings known as Kartagener 's syndrome ) and other heterotaxic defects. These left - right anatomic abnormalities can also result in congenital heart disease. It has been shown that proper cilial function is responsible for the normal left - right asymmetry in mammals. Ciliopathy as an origin for many multi-symptom genetic diseases Recent findings in genetic research have suggested that a large number of genetic disorders, both genetic syndromes and genetic diseases, that were not previously related in the medical literature, may be, in fact, highly related in the root cause of the widely varying set of medical symptoms that are clinically visible in the disorder. These have been grouped as an emerging class of diseases called ciliopathies. The underlying cause may be a dysfunctional molecular mechanism in the primary / immotile cilia, organelles which are present in many diverse cellular types throughout the human body. Cilia defects adversely affect numerous critical developmental signaling pathways essential to cellular development and thus offer a plausible hypothesis for the often multi-symptom nature of a large set of syndromes and diseases. Known ciliopathies include primary ciliary dyskinesia, Bardet - Biedl syndrome, polycystic kidney and liver disease, nephronophthisis, Alstrom syndrome, Meckel - Gruber syndrome, Sensenbrenner syndrome and some forms of retinal degeneration. See also Biological machines Flagellum Kinocilium Mucociliary clearance Protein domain dynamics Protein flexibility Stereocilia Undulipodia References Jump up ^ Mosby 's Medical, Nursing and Allied Health Dictionary, Fourth Edition, Mosby - Year Book Inc., 1994, p. 336 ^ Jump up to : Gardiner, Mary Beth ( September 2005 ). `` The Importance of Being Cilia '' ( PDF ). HHMI Bulletin. Howard Hughes Medical Institute. 18 ( 2 ). Retrieved 2008 - 07 - 26. Jump up ^ `` Cilium ''. biologydictionary.net. Retrieved 8 September 2017. Jump up ^ A Dictionary of Biology, 2004, accessed 2010 - 04 - 06. Jump up ^ Haimo LT, Rosenbaum JL ( December 1981 ). `` Cilia, flagella, and microtubules ''. J. Cell Biol. 91 ( 3 Pt 2 ) : 125s -- 130s. PMC 2112827. 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External links Brief summary of importance of cilia to many organs in human physiology The Ciliary Proteome Web Page at Johns Hopkins Structures of the cell / organelles ( TH H1. 00.01. 2 - 3 ) Endomembrane system Cell membrane Nucleus Nucleolus Endoplasmic reticulum Golgi apparatus Parenthesome Autophagosome Vesicles Exosome Lysosome Endosome Phagosome Vacuole Acrosome Cytoplasmic granules Melanosome Microbody Glyoxysome Peroxisome Weibel -- Palade body Cytoskeleton Microfilaments Intermediate filaments Microtubules Prokaryotic cytoskeleton MTOCs Centrosome Centriole Basal body Spindle pole body Myofibril Endosymbionts Mitochondrion Plastids Chloroplast Chromoplast Gerontoplast Leucoplast Amyloplast Elaioplast Proteinoplast Tannosome Other internal RNA Ribosome Spliceosome Vault Cytoplasm Proteasome External Undulipodium Cilium Flagellum Axoneme Radial spoke Extracellular matrix Cell wall Histology : Epithelial proteins ( TH H1. 00.01. 1 ) Lateral / cell - cell Cell adhesion molecules : Adherens junction Cadherin Desmosome Desmoglein Ion channels : Gap junction / Connexon Connexin Cytoskeleton : Desmosome Desmoplakin Plakoglobin Tonofibril other membrane proteins : Tight junction Claudin Occludin MARVELD2 Basal / cell - matrix Basal lamina Hemidesmosome / Tonofibril Focal adhesion Costamere Apical Cilia / Kinocilium Microvilli / Stereocilia ( STRC ) Microbiology : Protistology : Protists Former classifications Protozoa Mastigophora / Flagellates Sarcodina / Amoeboids Testate Heliozoa Infusoria / Ciliates Sporozoa Algae Cryptogams Thallophytes Fungus - like organisms Slime molds Ambiregnal protists Morphology Archaeplastida Chloroplastida `` green algae '' : Phycoplast Phragmoplast Flagellar apparatus Glaucophytes : Cyanelles Phycobilisomes Red algae : Pit connection Phycobilisomes Hacrobia Cryptophyta : Mastigonemes Periplast Haptophyte : Coccolith Haptonema Stramenopiles General : Mastigonemes Diatoms : Frustule Brown algae : Lamina Pneumatocyst Alveolata General : Alveoli Trichocyst Dinoflagellates : Dinokaryon Dinocyst Theca Ciliates : Cilium Cirrus Macronucleus Micronucleus Apicomplexans : Rhoptry Apicoplast Microneme Rhizaria Phytomyxea Cruciform division Excavate Kinetoplastids : Kinetoplast Glycosome Euglenoidea : Periplast / pellicle Amoebozoa Dictyostelids : Macrocyst Sorocarp Opisthokonta Choanoflagellates : Collar of microvilli General Levels of organization Unicellular Monadoid Amoeboid Coccoid Colonial s.s. Colonial flagellated Tetrasporal / capsal / palmelloid Sarcinoid Coenobial Filamentous / trichal / hyphal Parenchymatous Pseudoparenchymatous / plektenchymatic Membranous / thalloid / foliaceous Multinucleated Syncytial Coenocytic Siphonous Siphonocladous Multicellular s.s. / tissular / histonal Cell surface structures Simple cell membrane Mucilage Scale Frustule Cell wall Lorica Skeleton Test Theca Periplast / pellicle Locomotion Flagellum Cilium Pseudopodia Gliding motility Mitochondria Hydrogenosome Mitosome Nucleus Nucleomorph Multinucleate cells Plasmodium Dikaryon Heterokaryon Mitosis in protists Open Closed Orthomitosis Pleuromitosis Meiosis in protists Gametic Zygotic Sporic Other Cyst Cytostome Fimbriae Extrusome Contractile vacuole Eyespot apparatus Pyrenoid Axostyle Mastigont system Ecology and physiology Microbial ecology Microbial biogeography Baas - Becking hypothesis Development / Reproduction Life cycles Fertilization Nutrition : Autotrophy Phototrophy Heterotrophy Phagotrophy Osmotrophy Saprotrophy Parasitism Biotrophy Necrotrophy Mixotrophy Auxotrophy Retrieved from `` https://en.wikipedia.org/w/index.php?title=Cilium&oldid=807081296 '' Categories : Cell movement Organelles Hidden categories : Webarchive template wayback links Use dmy dates from June 2011 Talk Contents About Wikipedia Български Bosanski Català Čeština Dansk Deutsch Eesti Español Esperanto Euskara فارسی Français Galego Ido Bahasa Indonesia Íslenska Italiano Basa Jawa Қазақша Kreyòl ayisyen Latviešu Lietuvių Nederlands 日本 語 Norsk Norsk nynorsk Polski Português Română Русский Simple English Slovenčina Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska తెలుగు ไทย Türkçe Українська 中文 Edit links This page was last edited on 25 October 2017, at 19 : 46. 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Question: what type of cells have cilia and flagella
Answer: eukaryotes