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Encyclopedia > Eukaryote
Eukaryotes
Fossil range: Proterozoic - Recent
Scientific classification
Superdomain: Neomura
Domain: Eukarya
Whittaker & Margulis,1978
Kingdoms
Animalia - Animals
Plantae - Plants
Alternative phylogeny

Animals, plants, fungi, and protists are eukaryotes (IPA: [juːˈkæɹɪɒt]), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. The most characteristic membrane bound structure is the nucleus. This feature gives them their name, also spelled "eucaryote", which comes from the Greek ευ, meaning good/true, and κάρυον, meaning nut, referring to the nucleus. In the nucleus the genetic material, DNA, is arranged in chromosomes. Many eukaryotic cells also contain membrane-bound organelles such as mitochondria, chloroplasts and Golgi bodies. Eukaryotes often have unique flagella made of microtubules in a 9+2 arrangement. The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... For other uses, see Scientific classification (disambiguation). ... Domains Domain Archaea Domain Eukaryota Neomura is the hypothetical ancestor of the two domains of Archaea and Eukaryota. ... Robert Whittaker (1920-1980) was an American vegetation ecologist, active in the 1950s through the 1970s. ... Lynn Margulis Dr. Lynn Margulis (born March 15, 1938) is a biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst. ... Ernst Haeckels presentation of a three-kingdom system (Plantae, Protista, Animalia) in his 1866 Generelle Morphologie der Organismen). ... For other uses, see Animal (disambiguation). ... Subkingdom/Phyla Chytridiomycota Blastocladiomycota Neocallimastigomycota Glomeromycota Zygomycota Dikarya (inc. ... For other uses, see Plant (disambiguation). ... The chromalveolates (Chromalveolata) are a hypothetical grouping of eukaryotes, comprising the Chromista and alveolates, as suggested by Tom Cavalier-Smith. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all... Alternative taxonomical classifications are those which differ from the commonly accepted classifications in fundamental ways. ... Supergroups Opisthokonta Amoebozoa Unikont is a eukaryotic cell with a single flagellum, at least ancestrally. ... Subgroups Kingdom Animalia Kingdom Fungi Choanozoa Choanoflagellates Corallochytrids Mesomycetozoea Nucleariids The opisthokonts (Greek: (opisthō-) = rear, posterior + (kontos) = pole i. ... Phyla Radiata Cnidaria Ctenophora - Comb jellies Bilateria Protostomia Acoelomorpha Platyhelminthes - Flatworms Nemertina - Ribbon worms Gastrotricha Gnathostomulida - Jawed worms Micrognathozoa Rotifera - Rotifers Acanthocephala Priapulida Kinorhyncha Loricifera Entoprocta Nematoda - Roundworms Nematomorpha - Horsehair worms Cycliophora Mollusca - Mollusks Sipuncula - Peanut worms Annelida - Segmented worms Tardigrada - Water bears Onychophora - Velvet worms Arthropoda - Insects, etc. ... The opisthokonts are a broad group of eukaryotes, including both the animals and fungi, together with a few sorts of protists. ... For the fictional character, see Fungus the Bogeyman. ... Subgroups Mycetozoa(slime moulds) Archamoebae    Pelobiontida    Entamoebida Gymnamoebia Various others The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means of internal cytoplasmic flow. ... Supergroups Apusozoa Cabozoa    Rhizaria    Excavata Corticata    Archaeplastida    Chromalveolata A Bikont is a eukaryotic cell with two flagella, developed by a unique pathway. ... Orders Apusomonadida Ancyromonadida Hemimastigida The Apusozoa comprise several genera of flagellate protozoa. ... A Bikont is a eukaryotic cell with two flagella. ... Phyla Cercozoa Foraminifera Radiolaria The Rhizaria are a major line of protists. ... This article is about the protist group called excavates. ... Supergroups Archaeplastida Chromalveolata Corticata is a clade suggested by Cavalier-Smith to encompass the eukaryote supergroups of Archaeplastida and Chromalveolata. ... The Archaeplastida are a major line of eukaryotes, comprising the land plants, green and red algae, and a small group called the glaucophytes. ... The chromalveolates (Chromalveolata) are a hypothetical grouping of eukaryotes, comprising the Chromista and alveolates, as suggested by Tom Cavalier-Smith. ... For other uses, see Animal (disambiguation). ... For other uses, see Plant (disambiguation). ... Subkingdom/Phyla Chytridiomycota Blastocladiomycota Neocallimastigomycota Glomeromycota Zygomycota Dikarya (inc. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all... Articles with similar titles include the NATO phonetic alphabet, which has also informally been called the “International Phonetic Alphabet”. For information on how to read IPA transcriptions of English words, see IPA chart for English. ... “Life on Earth” redirects here. ... 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... Look up cell membrane in Wiktionary, the free dictionary. ... The eukaryotic cytoskeleton. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... 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. ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... Schematic of typical animal cell, showing subcellular components. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ... A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ... Microtubules are one of the components of the cytoskeleton. ...


Finally, cell division involves a complex way of separating the duplicated chromosomes, which is also mediated by complexly choreographed arrangements of microtubules. There are two methods. In mitosis one cell divides to produce two genetically identical cells. In meiosis, which is required in sexual reproduction, one diploid cell (having two copies of each chromosome, one from each parent) undergoes a process of recombination between each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes) each of which has only a single complement of chromosomes, each one being a unique mix and match of the corresponding pair of parental chromosomes. It has been suggested that Binary fission be merged into this article or section. ... Not to be confused with miosis. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... Recombination usually refers to the biological process of genetic recombination and meiosis, a genetic event that occurs during the formation of sperm and egg cells. ... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ...


Eukaryotes appear to be monophyletic and thus make up one of the three domains of life. The two other domains: bacteria and archaea (prokaryotes (without a nucleus)) share none of the above features, though the eukaryotes do share some aspects of their biochemistry with the archaea, and as such, are grouped with the archaea in the clade Neomura. In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ... In biology, a domain (also superregnum, superkingdom, or empire) is the top-level grouping of organisms in scientific classification, higher than a kingdom. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (), or archaebacteria, are a major group of microorganisms. ... Prokaryotes (pro-KAR-ee-oht) (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. ... Domains Domain Archaea Domain Eukaryota Neomura is the hypothetical ancestor of the two domains of Archaea and Eukaryota. ...

Contents

Differences between eukaryotic cells

There are many different types of eukaryotic cells, though animals and plants are the most familiar eukaryotes, and thus provide an excellent starting point for understanding eukaryotic structure. Fungi and many protists have some substantial differences, however.


Animal cell

Structure of a typical animal cell.
Structure of a typical plant cell.
Structure of a typical plant cell.

An animal cell is a form of eukaryotic cell which make up many tissues in animals. The animal cell is distinct from other eukaryotes, most notably plant cells, as they lack cell walls and chloroplasts, and they have smaller vacuoles. Due to the lack of a rigid cell wall, animal cells can adopt a variety of shapes and a phagocytic cell can even engulf other structures. Image File history File links Animal_cell_structure. ... Image File history File links Animal_cell_structure. ... A three-dimensional diagram of the animal cell, including its organelles. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Plant cell structure Plant cells are quite different from the cells of the other eukaryotic kingdoms organisms. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Biological tissue is a collection of interconnected cells that perform a similar function within an organism. ... For other uses, see Animal (disambiguation). ... The cells of plants are quite different from the cells of most other organisms. ... A cell wall is a fairly rigid layer surrounding a cell, located external to the cell membrane, that provides the cell with structural support, protection, and a filtering mechanism. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Schematic of typical animal cell, showing subcellular components. ... A cell wall is a fairly rigid layer surrounding a cell, located external to the cell membrane, that provides the cell with structural support, protection, and a filtering mechanism. ... A phagocyte is a cell that ingests and destroys foreign matter such as microorganisms or debris via a process known as phagocytosis. ...


Plant cell

Further information: Plant cell

Plant cells are quite different from the cells of the other eukaryotic organisms. Their distinctive features are: Plant cell structure Plant cells are quite different from the cells of the other eukaryotic kingdoms organisms. ... 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... “Life on Earth” redirects here. ...

Schematic of typical animal cell, showing subcellular components. ... Turgor (also called turgor pressure or osmotic pressure) is the pressure that can build in a space that is enclosed by a membrane that is permeable to a solvent of a solution such as water but not to the solutes of the soluton. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... The cytosol (cf. ... Leafhoppers and many other insects feed off plant sap Sap is the fluid transported in xylem cells (tracheids or vessel elements) or phloem sieve tube elements of a plant. ... A cell wall is a fairly rigid layer surrounding a cell, located external to the cell membrane, that provides the cell with structural support, protection, and a filtering mechanism. ... Cellulose as polymer of β-D-glucose Cellulose in 3D Cellulose (C6H10O5)n is a polysaccharide of beta-glucose. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Lignin (sometimes lignen) is a chemical compound (complex, highly cross-linked aromatic polymer) that is most commonly derived from wood and is an integral part of the cell walls of plants, especially in tracheids, xylem fibres and sclereids. ... Initially protoplast (in Greek: proton = first and platho = mould) referred to the first organized body of a species this meaning is similar to the non-biological definition, the first from from which all subsequent forms are derived. ... Look up cell membrane in Wiktionary, the free dictionary. ... Subkingdom/Phyla Chytridiomycota Blastocladiomycota Neocallimastigomycota Glomeromycota Zygomycota Dikarya (inc. ... Structure of the chitin molecule, showing two of the N-Acetylglucosamine units that repeat to form long chains in beta-1,4 linkage. ... Prokaryotes (pro-KAR-ee-oht) (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. ... Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of eubacteria. ... Plasmodesmata (Singular, plasmodesma) are small cell junctions in a plant cell which connect the cytoplasm of adjacent plant cells, forming a circulatory and communication system connecting the cells in plant tissue. ... Hyphae of Penicillium A hypha (plural hyphae) is a long, branching filamentous cell of a fungus, and also of unrelated Actinobacteria. ... Plant cells with visible chloroplasts. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Chlorophyll gives leaves their green color Space-filling model of the chlorophyll molecule Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. ... For other uses, see Plant (disambiguation). ... The leaf is the primary site of photosynthesis in plants. ... // A flagellum (plural: flagella) is a long, slender projection from the cell body, composed of microtubules and surrounded by the plasma membrane. ... Orders & Families Cordaitales † Pinales   Pinaceae - Pine family   Araucariaceae - Araucaria family   Podocarpaceae - Yellow-wood family   Sciadopityaceae - Umbrella-pine family   Cupressaceae - Cypress family   Cephalotaxaceae - Plum-yew family   Taxaceae - Yew family Vojnovskyales † Voltziales † The conifers, division Pinophyta, also known as division Coniferae, are one of 13 or 14 division level taxa within the... Classes Magnoliopsida - Dicots Liliopsida - Monocots The flowering plants or angiosperms are the most widespread group of land plants. ... A centriole is a barrel shaped organelle[1] found in most eukaryotic cells, though absent in higher plants and fungi. ... A three-dimensional diagram of the animal cell, including its organelles. ...

Fungal cell

Fungal cells are most similar to animal cells, with the following exceptions.

  • A cell wall made of chitin.
  • Less definition between cells. Higher fungal cells have porous separations called septa which allow the passage of cytoplasm, organelles, and sometimes, nuclei. Primitive fungi have no such divisions, and each organism is essentially a giant supercell. These fungi are described as coenocytic.
  • Only the most primitive fungi, chytrids, have flagella.

Structure of the chitin molecule, showing two of the N-Acetylglucosamine units that repeat to form long chains in beta-1,4 linkage. ... Look up septum in Wiktionary, the free dictionary. ... A coenocyte is a multinucleate cell. ... Orders Chytridiales Spizellomycetales Blastocladiales Monoblepharidales Neocallimasticales Chytridiomycota is a division of the Fungi kingdom and contains only one class, Chytridiomycetes. ...

Other eukaryotic cells

Eukaryotes are a very diverse group, and their cell structures are equally diverse. Many have cell walls, many do not. Many have chloroplasts, derived from primary, secondary, or even tertiary endosymbiosis, and many do not. Some groups have unique structures, such as the cyanelles of the glaucophytes, the haptonema of the haptophytes, or the ejectisomes of the cryptomonads. Other structures, such as pseudopods, are found in various eukaryote groups in different forms, such as the lobose amoebozoans or the reticulose foraminiferans. The glaucophytes, also referred to as glaucocystophytes or glaucocystids, are a tiny group of freshwater algae. ... Orders Class Pavlovophyceae    Pavlovales Class Prymnesiophyceae    Prymnesiales    Phaeocystales    Isochrysidales    Coccolithales The haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a group of algae. ... Typical genera Order Cryptomonadales    Campylomonas    Chilomonas    Chroomonas    Cryptomonas    Falcomonas    Geminigera    Guillardia    Hemiselmis    Plagioselmis    Proteomonas    Storeatula    Rhodomonas    Teleaulax Order Goniomonadales    Goniomonas The cryptomonads are a small group of flagellates, most of which have chloroplasts. ... Subgroups Mycetozoa(slime moulds) Archamoebae    Pelobiontida    Entamoebida Gymnamoebia Various others The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means of internal cytoplasmic flow. ... Orders Allogromiida Carterinida Fusulinida - extinct Globigerinida Involutinida - extinct Lagenida Miliolida Robertinida Rotaliida Silicoloculinida Spirillinida Textulariida incertae sedis    Xenophyophorea    Reticulomyxa The Foraminifera, (Hole Bearers) or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net. ...


Structure

Eukaryotic cells are generally much larger than prokaryotes. They have a variety of internal membranes and structures, called organelles, and a cytoskeleton composed of microtubules, microfilaments and intermediate filaments, which play an important role in defining the cell's organization and shape. Eukaryotic DNA is divided into several linear bundles called chromosomes, which are separated by a microtubular spindle during nuclear division. In addition to asexual cell division (mitosis), most eukaryotes have some process of sexual reproduction via cell fusion (meiosis), which is not found among prokaryotes. Prokaryotes (pro-KAR-ee-oht) (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. ... Schematic of typical animal cell, showing subcellular components. ... The eukaryotic cytoskeleton. ... Microtubules are one of the components of the cytoskeleton. ... This article or section should be merged with actin Microfilaments or actin filaments are made up of two twisted monomeric actin subunits. ... // Intermediate filaments (IFs) are important structural proteins which are located both in the cytoplasm and the nucleus. ... 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. ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... It has been suggested that Binary fission be merged into this article or section. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... Not to be confused with miosis. ...


Golgi apparatus Rough ER nucleus Nuclear envelope Nuclear pore Ribosome Smooth ER secretory vesicle Lysosome Plasma membrane

Detail of the endomembrane system and its components

Image File history File links Endomembrane_system_diagram. ...

Internal membrane

Eukaryotic cells include a variety of membrane-bound structures, collectively referred to as the endomembrane system. Simple compartments, called vesicles or vacuoles, can form by budding off other membranes. Many cells ingest food and other materials through a process of endocytosis, where the outer membrane invaginates and then pinches off to form a vesicle. It is probable that most other membrane-bound organelles are ultimately derived from such vesicles. The endomembrane system is the system of internal membranes within eukaryotic cells that divide the cell into functional and structural compartments, or organelles. ... This article or section is in need of attention from an expert on the subject. ... Schematic of typical animal cell, showing subcellular components. ... It has been suggested that Endocytic cycle be merged into this article or section. ...


The nucleus is surrounded by a double membrane (commonly referred to as a nuclear envelope), with pores that allow material to move in and out. Various tube- and sheet-like extensions of the nuclear membrane form what is called the endoplasmic reticulum or ER, which is involved in protein transport and maturation. It includes the Rough ER where ribosomes are attached, and the proteins they synthesize enter the interior space or lumen. Subsequently, they generally enter vesicles, which bud off from the Smooth ER. In most eukaryotes, this protein-carrying vesicles are released and further modified in stacks of flattened vesicles, called Golgi bodies or dictyosomes. 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. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ...


Vesicles may be specialized for various purposes. For instance, lysosomes contain enzymes that break down the contents of food vacuoles, and peroxisomes are used to break down peroxide which is toxic otherwise. Many protozoa have contractile vacuoles, which collect and expel excess water, and extrusomes, which expel material used to deflect predators or capture prey. In multicellular organisms, hormones are often produced in vesicles. In higher plants, most of a cell's volume is taken up by a central vacuole, which primarily maintains its osmotic pressure. Organelles labeled at upper left. ... Basic structure of a peroxisome Peroxisomes are ubiquitous organelles in eukaryotes that participate in the metabolism of fatty acids and other metabolites. ... A peroxide is a compound containing an oxygen-oxygen single bond. ... Extrusomes are membrane-bound structures in some eukaryotes which, under certain conditions, discharge their contents outside the cell. ... Norepinephrine A hormone (from Greek όρμή - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ...

Mitochondria structure: 1) Inner membrane 2) Outer membrane 3) Crista 4) Matrix
Mitochondria structure:
1) Inner membrane
2) Outer membrane
3) Crista
4) Matrix

Image File history File links Mitochondrie. ... Image File history File links Mitochondrie. ... The inner membrane is a membrane (phospholipid bilayer) of an organelle that is within the outer membrane. ... Mitochondria structure : 1) Inner membrane 2) Outer membrane 3) Crista 4) Matrix The outer membrane refers to the outside membranes of Gram-negative bacteria, the chloroplast, or the mitochondria. ... Mitochondria structure : 1) Inner membrane 2) Outer membrane 3) Crista 4) Matrix Cristae (singular crista) are the internal compartments formed by the inner membrane of a mitochondrion. ... In biology, the word matrix is used for the material between animal or plant cells, or generally the material (or tissue) in which more specialized structures are embedded, and also specifically for one part of the mitochondrion. ...

Mitochondria and plastids

Mitochondria are organelles found in nearly all eukaryotes. They are surrounded by double membranes (known as the phospholipid bi-layer), the inner of which is folded into invaginations called cristae, where aerobic respiration takes place. They contain their own DNA and are only formed by the fission of other mitochondria. They are now generally held to have developed from endosymbiotic prokaryotes, probably proteobacteria. The few protozoa that lack mitochondria have been found to contain mitochondrion-derived organelles, such as hydrogenosomes and mitosomes. Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... This fluid lipid bilayer cross section is made up entirely of phosphatidyl choline. ... This article or section should be merged with aerobic metabolism. ... An endosymbiont (also known as intracellular symbiont) is any organism that lives within cells of another organism, i. ... Orders Alpha Proteobacteria    Caulobacterales - e. ... A hydrogenosome is an organelle of ciliates, trichomonads and fungi. ... A mitosome is an organelle found in some unicellular eukaryotic organisms. ...


Plants and various groups of algae also have plastids. Again, these have their own DNA and developed from endosymbiotes, in this case cyanobacteria. They usually take the form of chloroplasts, which like cyanobacteria contain chlorophyll and produce energy through photosynthesis. Others are involved in storing food. Although plastids likely had a single origin, not all plastid-containing groups are closely related. Instead, some eukaryotes have obtained them from others through secondary endosymbiosis or ingestion. A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... Plant cells with visible chloroplasts. ... Orders The taxonomy of the Cyanobacteria is currently under revision. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Chlorophyll gives leaves their green color Space-filling model of the chlorophyll molecule Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. ... The leaf is the primary site of photosynthesis in plants. ...


Endosymbiotic origins have also been proposed for the nucleus, for which see below, and for eukaryotic flagella, supposed to have developed from spirochaetes. This is not generally accepted, both from a lack of cytological evidence and difficulty in reconciling this with cellular reproduction. // A flagellum (plural: flagella) is a long, slender projection from the cell body, composed of microtubules and surrounded by the plasma membrane. ... Families Spirochaetaceae Brachyspiraceae    Brachyspira    Serpulina Leptospiraceae    Leptospira    Leptonema Spirochaetes is a phylum of distinctive Gram-negative bacteria, which have long, helically coiled cells. ... Cytology (also known as Cell biology) is the scientific study of cells. ...


Cytoskeletal structures

Many eukaryotes have long slender motile cytoplasmic projections, called flagella. These are composed mainly of tubulin and shorter cilia, both of which are variously involved in movement, feeding, and sensation. These are entirely distinct from prokaryotic flagella. They are supported by a bundle of microtubules arising from a basal body, also called a kinetosome or centriole, characteristically arranged as nine doublets surrounding two singlets. Flagella also may have hairs, or mastigonemes, and scales connecting membranes and internal rods. Their interior is continuous with the cell's cytoplasm. Microfilamental structures composed by actin and actin binding proteins e.g. α-actinin, fimbrin, filamin are present in submembraneous cortical layers and bundles as well. Motor proteins of microtubules e.g. dynein or kinesin and actin e.g. myosins provide dynamic character of the network. // A flagellum (plural: flagella) is a long, slender projection from the cell body, composed of microtubules and surrounded by the plasma membrane. ... Tubulin is the protein which makes up microtubules. ... cross-section of two motile cilia, showing the 9+2 structure A cilium (plural cilia) or undulipodium (pl. ... A basal body is a short cylindrical array of microtubules plus their associated proteins found at the base of a eukaryotic cell cilium or flagellum. ... A kinetosome, in Biology, refers to the basal bodies found usually in ciliates. ... A centriole is a barrel shaped organelle[1] found in most eukaryotic cells, though absent in higher plants and fungi. ... Mastigonemes are lateral hairs found covering the flagella of heterokont and cryptophyte algae[1]. They are approximately 15 nm in diameter, and usually consist of a tubular shaft that itself terminates in smaller hairs. It is believed that they assist in locomotion by increasing the surface area of a flagellum. ... Organelles. ... G-Actin (PDB code: 1j6z). ... Actinin is a microfilament protein. ... Fimbrin - Wikipedia /**/ @import /skins/monobook/IE50Fixes. ... This is a list of gene families or gene complexes, that is sets of genes which occur across a number of different species which often serve similar biological functions. ... Dynein is a motor protein (also called molecular motor or motor molecule) in cells which converts the chemical energy contained in ATP into the mechanical energy of movement. ... The kinesin dimer attaches to, and moves along, microtubules. ... Part of the myosin structure, atoms in the heavy chain are colored red on the left-hand side, and atoms in the light chains are colored orange and yellow. ...


Centrioles are often present even in cells and groups that do not have flagella. They generally occur in groups of one or two, called kinetids, that give rise to various microtubular roots. These form a primary component of the cytoskeletal structure, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Centrioles may also be associated in the formation of a spindle during nuclear division. A centriole in biology is a hollow cylindrical organelle found in most animal cells, and cells of fungi and algae though not frequently in plants. ...


Significance of cytoskeletal structures is underlined in determination of shape of the cells as well as they are essential components of migratory responses like chemotaxis and chemokinesis. Some protists have various other microtubule-supported organelles. These include the radiolaria and heliozoa, which produce axopodia used in flotation or to capture prey, and the haptophytes, which have a peculiar flagellum-like organelle called the haptonema. Chemotaxis is a kind of taxis, in which bodily cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. ... There are very few or no other articles that link to this one. ... Possible classes Polycystinea Acantharea Taxopodea Radiolaria are amoeboid protozoa that produce intricate mineral skeletons, typically with a central capsule dividing the cell into inner and outer portions, called endoplasm and ectoplasm. ... Heliozoa, or sun animalcules, are roughly spherical amoeboids with many stiff, microtubule-supported projections called axopods radiating outward from the cell surface. ... Orders Class Pavlovophyceae    Pavlovales Class Prymnesiophyceae    Prymnesiales    Phaeocystales    Isochrysidales    Coccolithales The haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a group of algae. ...


Plant cell wall

Further information: Cell wall

Plant cells contain a cell wall, which is a fairly rigid layer surrounding a cell, located external to the cell membrane, that provides the cell with structural support, protection, and a filtering mechanism. The cell wall also prevents over-expansion when water enters the cell. The major carbohydrates making up the primary cell wall are cellulose, hemicellulose and pectin. The cellulose microfibrils are linked via hemicellulosic tethers to form the cellulose-hemicellulose network, which is embedded in the pectin matrix. The most common hemicellulose in the primary cell wall is xyloglucan. A cell wall is a fairly rigid layer surrounding a cell, located external to the cell membrane, that provides the cell with structural support, protection, and a filtering mechanism. ... 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... Look up cell membrane in Wiktionary, the free dictionary. ... Cellulose as polymer of β-D-glucose Cellulose in 3D Cellulose (C6H10O5)n is a polysaccharide of beta-glucose. ... A hemicellulose can be any of several heteropolymers (matrix polysaccharides) present in almost all cell walls along with cellulose. ... Pectin, a white to light brown powder, is a heterosaccharide derived from the cell wall of higher terrestrial plants. ... The microfibril is a very fine fibril, or fiber-like strand, consisting of glycoproteins. ... Xyloglucan is the main hemicellulose in the primary cell wall of dicotyledonous plants. ...


Reproduction

Nuclear division is often coordinated with cell division. This generally takes place by mitosis, a process which allows each daughter nucleus to receive one copy of each chromosome. In most eukaryotes there is also a process of sexual reproduction, typically involving an alternation between haploid generations, where only one copy of each chromosome is present, and diploid generations, where two are present, occurring through nuclear fusion (syngamy) and meiosis. There is considerable variation in this pattern, however. This does not adequately cite its references or sources. ... It has been suggested that Binary fission be merged into this article or section. ... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... Not to be confused with miosis. ...


Eukaryotes have a smaller surface to volume area ratio than prokaryotes, and thus have lower metabolic rates and longer generation times. In some multicellular organisms, cells specialized for metabolism will have enlarged surface areas, such as intestinal vili.


Origin and evolution

The original, now outdated, five-kingdom system.
The original, now outdated, five-kingdom system.

The origin of the eukaryotic cell was a milestone in the evolution of life, since they include all complex cells and almost all multi-cellular organisms. The timing of this series of events is hard to determine; Knoll (1992) suggests they developed approximately 1.6 - 2.1 billion years ago. Fossils that are clearly related to modern groups start appearing around 1.2 billion years ago, in the form of a red alga. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Possible classes Florideophyceae Bangiophyceae Cyanidiophyceae The red algae (Rhodophyta, IPA: , from Greek: (rhodon) = rose + (phyton) = plant, thus red plant) are a large group, about 5000 - 6000 species [1] of mostly multicellular, marine algae, including many notable seaweeds. ...


rRNA trees constructed during the 1980s and 1990s left most eukaryotes in an unresolved "crown" group (not technically a true crown), which was usually divided by the form of the mitochondrial cristae. The few groups that lack mitochondria branched separately and so the absence was believed to be primitive, but this is now considered an artifact of long branch attraction and they are known to have lost them secondarily. A non-coding RNA (ncRNA) is any RNA molecule that functions without being translated into a protein. ... The 1980s refers to the years from 1980 to 1989. ... For the band, see 1990s (band). ... A crown group is a living monophyletic group or clade, consisting of the last common ancestor of all living examples, plus all of its descendants. ... Long branch attraction (LBA) is a phenomenon in phylogenetic analyses (most commonly those employing maximum parsimony) when rapidly evolving lineages are inferred to be closely related, regardless of their true evolutionary relationships. ...


Trees based on actin and other molecules have painted a different and more complete picture. Most eukaryotes are now included in several supergroups: G-Actin (PDB code: 1j6z). ...

Opisthokonts Animals, fungi, choanoflagellates, etc.
Amoebozoa Most lobose amoebae and slime moulds
Rhizaria Foraminifera, Radiolaria, and various other amoeboid protozoa
Excavates Various flagellate protozoa
Archaeplastida (or Primoplantae) Land plants, green algae, red algae, and glaucophytes
Chromalveolates Heterokonts, Haptophytes, Cryptomonads, and Alveolates.
 
Eukarya
Bikonta

Apusozoa The opisthokonts (Greek opistho- rear, posterior + kontos pole i. ... For other uses, see Animal (disambiguation). ... Subkingdom/Phyla Chytridiomycota Blastocladiomycota Neocallimastigomycota Glomeromycota Zygomycota Dikarya (inc. ... The choanoflagellates are a group of flagellate protozoa. ... Subgroups Mycetozoa(slime moulds) Archamoebae    Pelobiontida    Entamoebida Gymnamoebia Various others The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means of internal cytoplasmic flow. ... Alternate meanings: Amoeboid, Amoebozoa For other uses, see Amoeba (disambiguation). ... Typical orders Protostelia    Protosteliida Myxogastria    Liceida    Echinosteliida    Trichiida    Stemonitida    Physarida Dictyostelia    Dictyosteliida Slime mould (or slime mold) is a broad term often referring to roughly 6 groups of Eukaryotes. ... Phyla Cercozoa Foraminifera Radiolaria The Rhizaria are a major line of protists. ... Orders Allogromiida Carterinida Fusulinida - extinct Globigerinida Involutinida - extinct Lagenida Miliolida Robertinida Rotaliida Silicoloculinida Spirillinida Textulariida incertae sedis    Xenophyophorea    Reticulomyxa The Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands that branch and merge to form a dynamic net. ... Possible classes Polycystinea Acantharea Taxopodea Radiolaria are amoeboid protozoa that produce intricate mineral skeletons, typically with a central capsule dividing the cell into inner and outer portions, called endoplasm and ectoplasm. ... Amoeba (Chaos diffluens) Foraminiferan (Ammonia tepida) Heliozoan (Actinophrys sol) Amoeboids are cells that move or feed by means of temporary projections, called pseudopods (false feet). ... The excavates are a major line of protists, often known as Excavata. ... Flagellata from Ernst Haeckels Artforms of Nature, 1904 Parasitic excavate (Giardia lamblia) Green alga (Chlamydomonas) Flagellates are cells with one or more whip-like organelles called flagella. ... The Archaeplastida are a major line of eukaryotes, comprising the land plants, green and red algae, and a small group called the glaucophytes. ... Divisions Non-vascular land plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses †Horneophytopsida Vascular plants (tracheophytes) †Rhyniophyta—rhyniophytes †Zosterophyllophyta—zosterophylls Lycopodiophyta—clubmosses †Trimerophytophyta—trimerophytes Pteridophyta - ferns and horsetails Ophioglossophyta - adders-tongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants The embryophytes... Divisions Chlorophyta Charophyta Streptophytina (Subdivision) The green algae are the large group of algae from which the embryophytes (higher plants) emerged. ... Possible classes Florideophyceae Bangiophyceae Cyanidiophyceae Red algae (Rhodophyta, pronounced /ˈrəʊdÉ™(ÊŠ)ËŒfʌɪtÉ™/) are a large group of mostly multicellular, marine algae, including many notable seaweeds. ... The glaucophytes, also referred to as glaucocystophytes or glaucocystids, are a tiny group of freshwater algae. ... Phyla Heterokontophyta Haptophyta Cryptophyta Alveolata Ciliophora Apicomplexa Dinoflagellata Chromalveolata is a eukaryote supergroup first proposed by Thomas Cavalier-Smith as a refinement of his kingdom Chromista, which was first proposed in 1981. ... Typical classes Colored groups Chrysophyceae (golden algae) Synurophyceae Actinochrysophyceae (axodines) Pelagophyceae Phaeothamniophyceae Bacillariophyceae (diatoms) Bolidophyceae Raphidophyceae Eustigmatophyceae Xanthophyceae (yellow-green algae) Phaeophyceae (brown algae) Colorless groups Oomycetes (water moulds) Hypochytridiomycetes Bicosoecea Labyrinthulomycetes (slime nets) Opalinea Proteromonadea The heterokonts or stramenopiles are a major line of eukaryotes containing about 10,500... Orders Class Pavlovophyceae    Pavlovales Class Prymnesiophyceae    Prymnesiales    Phaeocystales    Isochrysidales    Coccolithales The haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a group of algae. ... Typical genera Order Cryptomonadales    Campylomonas    Chilomonas    Chroomonas    Cryptomonas    Falcomonas    Geminigera    Guillardia    Hemiselmis    Plagioselmis    Proteomonas    Storeatula    Rhodomonas    Teleaulax Order Goniomonadales    Goniomonas The cryptomonads are a small group of flagellates, most of which have chloroplasts. ... The alveolates are a major line of protists. ... Supergroups Apusozoa Cabozoa    Rhizaria    Excavata Corticata    Archaeplastida    Chromalveolata A Bikont is a eukaryotic cell with two flagella, developed by a unique pathway. ... Orders Apusomonadida Ancyromonadida Hemimastigida The Apusozoa comprise several genera of flagellate protozoa. ...


Corticata

Archaeplastida Supergroups Archaeplastida Chromalveolata Corticata is a clade suggested by Cavalier-Smith to encompass the eukaryote supergroups of Archaeplastida and Chromalveolata. ... The Archaeplastida are a major line of eukaryotes, comprising the land plants, green and red algae, and a small group called the glaucophytes. ...



Chromalveolata The chromalveolates (Chromalveolata) are a hypothetical grouping of eukaryotes, comprising the Chromista and alveolates, as suggested by Tom Cavalier-Smith. ...



Cabozoa

Rhizaria A Bikont is a eukaryotic cell with two flagella. ... Phyla Cercozoa Foraminifera Radiolaria The Rhizaria are a major line of protists. ...



Excavata This article is about the protist group called excavates. ...




Unikonta

Amoebozoa Supergroups Opisthokonta Amoebozoa Unikont is a eukaryotic cell with a single flagellum, at least ancestrally. ... Subgroups Mycetozoa(slime moulds) Archamoebae    Pelobiontida    Entamoebida Gymnamoebia Various others The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means of internal cytoplasmic flow. ...


Opisthokonta

Metazoa Subgroups Kingdom Animalia Kingdom Fungi Choanozoa Choanoflagellates Corallochytrids Mesomycetozoea Nucleariids The opisthokonts (Greek: (opisthō-) = rear, posterior + (kontos) = pole i. ... Phyla Radiata Cnidaria Ctenophora - Comb jellies Bilateria Protostomia Acoelomorpha Platyhelminthes - Flatworms Nemertina - Ribbon worms Gastrotricha Gnathostomulida - Jawed worms Micrognathozoa Rotifera - Rotifers Acanthocephala Priapulida Kinorhyncha Loricifera Entoprocta Nematoda - Roundworms Nematomorpha - Horsehair worms Cycliophora Mollusca - Mollusks Sipuncula - Peanut worms Annelida - Segmented worms Tardigrada - Water bears Onychophora - Velvet worms Arthropoda - Insects, etc. ...



Choanozoa The opisthokonts are a broad group of eukaryotes, including both the animals and fungi, together with a few sorts of protists. ...



Eumycota For the fictional character, see Fungus the Bogeyman. ...





Modern cladogram of Eukarya

Several authorities recognize two larger clades, the unikonts and the bikonts, the unikonts deriving from an ancestral uniflagellar organism, and the bikonts deriving from an ancestral biflagellate. In this system, the opisthokonts and amoebozoans are considered unikonts, and the rest are considered bikonts. The chromalveolates were originally thought to be two separate groups, the chromists and the alveolates, but the former was proved to be paraphyletic to the latter, and the two groups combined. Some small protist groups have not been related to any of these supergroups, in particular the centrohelids. Eukaryotes are closely related to Archaea, at least in terms of nuclear DNA and genetic machinery, and are placed by some, along with the Archaea, in the clade Neomura. In other respects, such as membrane composition, they are similar to eubacteria. Three main explanations for this have been proposed: Supergroups Opisthokonta Amoebozoa Unikont is a eukaryotic cell with a single flagellum, at least ancestrally. ... A Bikont is a eukaryotic cell with two flagella. ... Phyla Heterokontophyta Haptophyta Cryptophyta Alveolata Ciliophora Apicomplexa Dinoflagellata Chromalveolata is a eukaryote supergroup first proposed by Thomas Cavalier-Smith as a refinement of his kingdom Chromista, which was first proposed in 1981. ... Phyla Heterokontophyta Haptophyta Cryptophyta The Chromista are a eukaryotic supergroup, which may be treated as a separate kingdom or included among the Protista. ... The alveolates are a major line of protists. ... Families Raphidiophryidae Acanthocystidae Heterophryidae The centrohelids, or Centroheliozoa, are a large group of heliozoan protists, including both mobile and sessile forms found in both freshwater and marine environments, especially at some depth. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (), or archaebacteria, are a major group of microorganisms. ... Domains Domain Archaea Domain Eukaryota Neomura is the hypothetical ancestor of the two domains of Archaea and Eukaryota. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ...

  • Eukaryotes resulted from the complete fusion of two or more cells, the cytoplasm forming from a eubacterium and the nucleus from an archaeon (alternatively a virus).
  • Eukaryotes developed from Archaea, and acquired their eubacterial characteristics from the proto-mitochondrion.
  • Eukaryotes and Archaea developed separately from a modified eubacterium.

The final hypothesis is currently the most accepted. The origin of the endomembrane system and mitochondria are also disputed. The phagotrophic hypothesis states the membranes originated with the development of endocytosis and later specialized; mitochondria were acquired by ingestion, like plastids. The syntrophic hypothesis states that the proto-eukaryote relied on the proto-mitochondrion for food, and so ultimately grew to surround it; the membranes originate later, in part thanks to mitochondrial genes (the hydrogen hypothesis is one particular version). This article or section is in need of attention from an expert on the subject. ... The Hydrogen hypothesis is a model that describes how the first eukaryotic cell may have developed. ...


See also

The nematode worm Caenorhabditis elegans was the first multicellular organism to have its complete genome sequence determined. ...

References

  • Knoll AH (1992). "The early evolution of eu-karyotes: A geological perspective". Science 256 (5057): 622–27. doi:10.1126/science.1585174. 
  • T. Cavalier-Smith (2002). "The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa". International Journal of Systematic and Evolutionary Microbiology 52: 297-354. 
  • W. Martin & M.J. Russell (1992). "On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells". Philosophical Transactions of the Royal Society B. 
  • S. L. Baldauf (2003). "The Deep Roots of Eukaryotes". Science 300 (5626): 1703–1706. doi:10.1126/science.1085544. 
  • Sina M. Adl et al (2005). "The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists". Journal of Eukaryotic Microbiology 52 (5): 399. doi:10.1111/j.1550-7408.2005.00053.x. 

This article contains material from the Science Primer published by the NCBI, which, as a U.S. government publication, is in the public domain. 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. ... Science is the journal of the American Association for the Advancement of Science (AAAS). ... 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. ... National Center for Biotechnology Information logo The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health. ... The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ...

External links

  • Bacterial news
  • Eukaryotes (Tree of Life web site)

  Results from FactBites:
 
Eukaryote definition - Medical Dictionary definitions of popular medical terms (318 words)
Eukaryotes include all organisms except bacteria, viruses, and certain (blue-green) algae which, by contrast, are prokaryotes.
The origin of the eukaryotic cell was a milestone in the evolution of life.
Although eukaryotes use the same genetic code and metabolic processes as prokaryotes, their higher level of organizational complexity has permitted the development of truly multicellular organisms.
  More results at FactBites »

 
 

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