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Encyclopedia > Keratin
Microscopy of keratin filaments inside cells.
Microscopy of keratin filaments inside cells.

Keratins are a family of fibrous structural proteins; tough and insoluble, they form the hard but nonmineralized structures found in reptiles, birds, amphibians and mammals. They are rivaled as biological materials in toughness only by chitin. Kerogens are chemical compounds that make up a portion of the organic matter in sedimentary rocks. ... β-Carotene represented by a 3-dimensional stick diagram Carotene is responsible for the orange colour of the carrots and many other fruits and vegetables. ... Image File history File links KeratinF9. ... Image File history File links KeratinF9. ... Fibrous proteins, also called scleroproteins, are long filamentous protein molecules that form one of the two main classes of tertiary structure protein (the other being globular proteins). ... For other uses, see Mineral (disambiguation). ... Reptilia redirects here. ... For other uses, see Bird (disambiguation). ... For other uses, see Amphibian (disambiguation). ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the presence of sweat glands, including those that produce milk, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex... Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: βίος, bio, life; and λόγος, logos, knowledge), also referred to as the biological sciences, is the study of living organisms utilizing the scientific method. ... Structure of the chitin molecule, showing two of the N-Acetylglucosamine units that repeat to form long chains in beta-1,4 linkage. ...


There are various types of keratins within a single animal. For other uses, see Animal (disambiguation). ...

Contents

Variety of animal uses

Keratins are the main constituent of structures that grow from the skin:

Arthropods such as crustaceans often have parts of their armor or exoskeleton made of keratin, sometimes in combination with chitin. For the 1968 stage production, see Hair (musical), for the 1979 film, see Hair (film). ... For other uses, see Wool (disambiguation). ... Highland cow, a very old long-horned breed from Scotland. ... For other uses, see Nail. ... Cat claw A claw is a curved pointed appendage, found at the end of a toe or finger or, in arthropods, of the tarsus. ... Rear hooves of a Horse A hoof is the horny covering of the end of the foot in ungulate mammals. ... β-keratin or beta-keratin (not to be confused with β-carotene) is in contrast to alpha-keratin, a fibrous protein rich in alpha helices, rich in stacked β pleated sheets. ... In this SEM image of a butterfly wing the scales are clearly visible, and the tiny platelets on each individual scale are just barely visible in the striping. ... Orders  Crocodilia - Crocodilians scary crocodiles. ... Various seashells Danielle A shell is the hard, rigid outer covering, or integument, allanimals. ... Families See text Turtles are reptiles of the order Testudinata, most of whose body is shielded by a special bony shell developed from their ribs. ... This article or section is in need of attention from an expert on the subject. ... For other uses, see Turtle (disambiguation). ... Look up terrapin in Wiktionary, the free dictionary. ... Two feathers Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds. ... The beak, bill or rostrum is an external anatomical structure of birds which, in addition to eating, is used for grooming, manipulating objects, killing prey, probing for food, courtship, and feeding their young. ... For other meanings of bird, see bird (disambiguation). ... Diagram of β-pleated sheet with H-bonding between protein strands The β sheet (also β-pleated sheet) is the second form of regular secondary structure in proteins — the first is the alpha helix — consisting of beta strands connected laterally by three or more hydrogen bonds, forming a generally twisted, pleated sheet. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - Trilobites (extinct) Subphylum Chelicerata Arachnida - Spiders, Scorpions, etc. ... Classes Remipedia Cephalocarida Branchiopoda Ostracoda Maxillopoda Malacostraca The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum. ... Armour in animals is external or superficial protection against attack by predators, formed as part of the body (rather than the behavioural use of protective external objects), usually through the hardening of body tissues, outgrowths or secretions. ... An exoskeleton is an external anatomical feature that supports and protects an animals body, in contrast to the internal endoskeleton of, for example, a human. ... Structure of the chitin molecule, showing two of the N-Acetylglucosamine units that repeat to form long chains in beta-1,4 linkage. ...


The baleen plates of filter-feeding whales are made of them. Baleen hair is attached to the baleen plate Baleen (also called whalebone) is a substance made of keratin and is therefore stiff but somewhat elastic. ... This article is about the animal. ...


They can be integrated in the chitinophosphatic material that makes up the shell and setae in many brachiopods. The hard, rigid outer calcium carbonate covering of certain animals is called a shell. ... A seta is a stiff hair, bristle, or bristle-like process or part of an organism. ... Diversity About 4000 genera Subphyla and classes See Classification Brachiopods (from Latin bracchium, arm + New Latin -poda, foot) are a nearly extinct, small phylum of benthic invertebrates. ...


Keratins are also found in the gastrointestinal tracts of many animals, including roundworms (who also have an outer layer made of keratin). Gut redirects here. ... Classes Adenophorea    Subclass Enoplia    Subclass Chromadoria Secernentea    Subclass Rhabditia    Subclass Spiruria    Subclass Diplogasteria The roundworms or nematodes (Phylum Nematoda from Gr. ...


Although it is now difficult to be certain, the scales, claws, some protective armour and the beaks of dinosaurs would, almost certainly, have been composed of a type of keratin. Clades Tatisaurus Scutellosaurus Emausaurus Eurypoda Ankylosauria Stegosauria The Thyreophora (shield bearers, often known simply as armored dinosaurs - Greek: θυρεος, a large oblong shield, like a door and φορεω, I carry) were a subgroup of the ornithischian dinosaurs. ... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ...


In Crossopterygian fish, the outer layer of cosmoid scales was keratin. ... In this SEM image of a butterfly wing the scales are clearly visible, and the tiny platelets on each individual scale are just barely visible in the striping. ...


Cornification

In mammals there are soft epithelial keratins, the cytokeratins, and harder hair keratins. As certain skin cells differentiate and become cornified, pre-keratin polypeptides are incorporated into intermediate filaments. Eventually the nucleus and cytoplasmic organelles disappear, metabolism ceases and cells undergo a programmed death as they become fully keratinized. In zootomy, epithelium is a tissue composed of a layer of cells. ... Categories: Cell biology stubs | Keratins ... Hair keratin is a type of keratin found in hair and nails. ... Embryonic stem cells differentiate into cells in various body organs. ... Peptides are the family of molecules formed from the linking, in a defined order, of various amino acids. ... // Intermediate filaments (IFs) are important structural proteins which are located both in the cytoplasm and the nucleus. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... Cross section of cell with cytoplasm labeled at center right. ... Schematic of typical animal cell, showing subcellular components. ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... A section of mouse liver showing an apoptotic cell indicated by an arrow Apoptosis (pronounced apo tō sis) is a process of suicide by a cell in a multicellular organism. ...


Cells in the epidermis contain a structural matrix of keratin which makes this outermost layer of the skin almost waterproof, and along with collagen and elastin, gives skin its strength. Rubbing and pressure cause keratin to proliferate with the formation of protective calluses — useful for athletes and on the fingertips of musicians who play stringed instruments. Keratinized epidermal cells are constantly shed and replaced (see dandruff). 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... Cross-section of all skin layers Optical Coherence Tomography tomogram of fingertip, depicting stratum corneum (~500µm thick) with stratum disjunctum on top and stratum lucidum (connection to stratum spinosum) in the middle. ... Beyond overall skin structure, refer below to: See-also. ... Tropocollagen triple helix. ... Elastin is a protein in connective tissue that is elastic and allows many tissues in the body to resume their shape after stretching or contracting. ... This article is about calluses and corns of human skin. ... For the album by Ivor Cutler, see Dandruff (album). ...


These hard, integumentary structures are formed by intercellular cementing of fibers formed from the dead, cornified cells generated by specialized beds deep within the skin. Hair grows continuously and feathers moult and regenerate. The constituent proteins may be phylogenetically homologous but differ somewhat in chemical structure and supermolecular organization. The evolutionary relationships are complex and only partially known. Multiple genes have been identified for the β-keratins in feathers, and this is probably characteristic of all keratins. In zootomy, the integumentary system is the external covering of the body, comprised of the skin, hair, feathers, scales, nails, sweat glands and their products (sweat and mucus). ... The sebaceous glands are glands found in the skin of mammals. ... In animals, moulting (Commonwealth English) or molting (American English) is the routine shedding off old feathers in birds, or of old skin in reptiles, or of old hairs in mammals (see also coat (dog)). In arthropods, such as insects, arachnids and crustaceans, moulting describes the shedding of its exoskeleton (which... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Phylogenetic groups, or taxa, can be monophyletic, paraphyletic, or polyphyletic. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ... Look up chemical compound in Wiktionary, the free dictionary. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... This article is about evolution in biology. ... For other uses, see Gene (disambiguation). ...


Molecular biology and biochemistry

The properties which make structural proteins like keratins useful depend on their supermolecular aggregation. These depend on the properties of the individual polypeptide strands, which depend in turn on their amino acid composition and sequence. The α-helix and β-sheet motifs, and disulfide bridges, are crucial to the conformations of globular, functional proteins like enzymes, many of which operate semi-independently, but they take on a completely dominant role in the architecture and aggregation of keratins. Peptides (from the Greek πεπτος, digestible), are the family of short molecules formed from the linking, in a defined order, of various α-amino acids. ... This article is about the class of chemicals. ... Side view of an α-helix of alanine residues in atomic detail. ... Diagram of β-pleated sheet with H-bonding between protein strands The β sheet (also β-pleated sheet) is the second form of regular secondary structure in proteins — the first is the alpha helix — consisting of beta strands connected laterally by three or more hydrogen bonds, forming a generally twisted, pleated sheet. ... Proteins are an important class of biological macromolecules present in all biological organisms, made up of such elements as carbon, hydrogen, nitrogen, oxygen, and sulfur. ... 3-dimensional structure of hemoglobin, a globular protein. ... Neuraminidase ribbon diagram An enzyme (in Greek en = in and zyme = blend) is a protein, or protein complex, that catalyzes a chemical reaction and also controls the 3D orientation of the catalyzed substrates. ...


Glycine and alanine

Keratins contain a high proportion of the smallest of the 20 amino acids, glycine, whose "side group" is a single hydrogen atom; also the next smallest, alanine, with a small and noncharged methyl group. In the case of β-sheets, this allows sterically-unhindered hydrogen bonding between the amino and carboxyl groups of peptide bonds on adjacent protein chains, facilitating their close alignment and strong binding. Fibrous keratin molecules can twist around each other to form helical intermediate filaments. For the plant, see Glycine (plant). ... The term Side chain can have different meanings depending on the context: In chemistry and biochemistry a side chain is a part of a molecule attached to a core structure. ... Depiction of a hydrogen atom showing the diameter as about twice the Bohr model radius. ... Alanine (Ala, A) also 2-aminopropanoic acid is a non-essential α-amino acid. ... Methyl group In chemistry, a methyl group is a hydrophobic alkyl functional group derived from methane (CH4). ... Steric effects are the interaction of molecules dictated by their shape and/or spatial relationships. ... An example of a quadruple hydrogen bond between a self-assembled dimer complex reported by Meijer and coworkers. ... The general structure of an amine Amines are organic compounds and a type of functional group that contain nitrogen as the key atom. ... In chemistry, a carboxyl group is a functional group consisting of a carbon atom doubly bonded to an oxygen atom and single-bonded to a hydroxyl (-OH) group, typically written as -COOH: where R is a hydrogen or an organic group. ... A peptide bond is a chemical bond that is formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). ... A helix (pl: helices), from the Greek word έλικας/έλιξ, is a twisted shape like a spring, screw or a spiral (correctly termed helical) staircase. ...


Limited interior space is the reason why the triple helix of the (unrelated) structural protein collagen, found in skin, cartilage and bone, likewise has a high percentage of glycine. The connective tissue protein elastin also has a high percentage of both glycine and alanine. Silk fibroin, considered a β-keratin, can have these two as 75–80% of the total, with 10–15% serine, with the rest having bulky side groups. The chains are antiparallel, with an alternating C → N orientation.[1] A preponderance of amino acids with small, nonreactive side groups is characteristic of structural proteins, for which H-bonded close packing is more important than chemical specificity. Tropocollagen triple helix. ... Cartilage is a type of dense connective tissue. ... This article is about the skeletal organs. ... Elastin is a protein in connective tissue that is elastic and allows many tissues in the body to resume their shape after stretching or contracting. ... Fibroin is a type of protein created by silkworms in the production of silk. ... For other uses, see Chemical reaction (disambiguation). ... Chemical specificity is the ability of a proteins binding site to bind specific ligands. ...


Disulfide bridges

In addition to intra- and intermolecular hydrogen bonds, keratins have large amounts of the sulfur-containing amino acid cysteine, required for the disulfide bridges that confer additional strength and rigidity by permanent, thermally-stable crosslinking—a role sulfur bridges also play in vulcanized rubber. Human hair is approximately 14% cysteine. The pungent smells of burning hair and rubber are due to the sulfur compounds formed. Extensive disulfide bonding contributes to the insolubility of keratins, except in dissociating or reducing agents such as urea. This article is about the chemical element. ... Cysteine is a naturally occurring, sulfur-containing amino acid that is found in most proteins, although only in small quantities. ... In chemistry, a disulfide bond is a single covalent bond derived from the coupling of thiol groups. ... Vulcanization is an example of cross-linking. ... Vulcanization refers to a specific curing process of rubber involving high heat and the addition of sulfur. ... This does not cite any references or sources. ... It has been suggested that this article or section be merged with Solution. ... Dissociation in chemistry and biochemistry is a general process in which complexes, molecules, or salts separate or split into smaller molecules, ions, or radicals, usually in a reversible manner. ... Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... Urea is an organic compound with the chemical formula (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Nonproprietary Names (rINN) in use in Europe. ...


The more flexible and elastic keratins of hair have fewer interchain disulfide bridges than the keratins in mammalian fingernails, hooves and claws (homologous structures), which are harder and more like their analogs in other vertebrate classes. Hair and other α-keratins consist of α-helically-coiled single protein strands (with regular intra-chain H-bonding), which are then further twisted into superhelical ropes that may be further coiled. The β-keratins of reptiles and birds have β-pleated sheets twisted together, then stabilized and hardened by disulfide bridges. This article discusses the anatomical nail. ... Side view of an α-helix of alanine residues in atomic detail. ... An example of a quadruple hydrogen bond between a self-assembled dimer complex reported by Meijer and coworkers. ...


Silk

The silk fibroins produced by insects and spiders are often classified as keratins, though it is unclear whether they are phylogenetically related to vertebrate keratins. For other uses of this word, see Silk (disambiguation). ... Fibroin is a type of protein created by silkworms in the production of silk. ... Orders Subclass Apterygota Archaeognatha (bristletails) Thysanura (silverfish) Subclass Pterygota Infraclass Paleoptera (Probably paraphyletic) Ephemeroptera (mayflies) Odonata (dragonflies and damselflies) Infraclass Neoptera Superorder Exopterygota Grylloblattodea (ice-crawlers) Mantophasmatodea (gladiators) Plecoptera (stoneflies) Embioptera (webspinners) Zoraptera (angel insects) Dermaptera (earwigs) Orthoptera (grasshoppers, etc) Phasmatodea (stick insects) Blattodea (cockroaches) Isoptera (termites) Mantodea (mantids) Psocoptera... Diversity 111 families, 40,000 species Suborders Mesothelae Mygalomorphae Araneomorphae  See table of families Wikispecies has information related to: Spiders Spiders are predatory invertebrate animals that have two body segments, eight legs, no chewing mouth parts and no wings. ...


Silk found in insect pupae, and in spider webs and egg casings, also has twisted β-pleated sheets incorporated into fibers wound into larger supermolecular aggregates. The structure of the spinnerets on spiders’ tails, and the contributions of their interior glands, provide remarkable control of fast extrusion. Spider silk is typically about 1 to 2 micrometres (µm) thick, compared with about 60 µm for human hair, and more for some mammals. (Hair, or fur, occurs only in mammals.) The biologically and commercially useful properties of silk fibers depend on the organization of multiple adjacent protein chains into hard, crystalline regions of varying size, alternating with flexible, amorphous regions where the chains are randomly coiled.[2] A somewhat analogous situation occurs with synthetic polymers such as nylon, developed as a silk substitute. Silk from the hornet cocoon contains doublets about 10 µm across, with cores and coating, and may be arranged in up to 10 layers; also in plaques of variable shape. Adult hornets also use silk as a glue, as do spiders. Cockchafer (Melolontha melolontha) pupa Chrysalis redirects here: for other meanings see Chrysalis (disambiguation). ... Spiders web redirects here. ... A spinneret is a spiders silk spinning organ. ... Human submaxillary gland. ... Extruded aluminium; slots allow bars to be joined with special connectors. ... For other uses, see Fur (disambiguation). ... Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: βίος, bio, life; and λόγος, logos, knowledge), also referred to as the biological sciences, is the study of living organisms utilizing the scientific method. ... This article does not cite any references or sources. ... Spider silk is a fibre secreted by spiders. ... For other uses, see Crystal (disambiguation). ... An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. ... Illustration of a 3-dimensional polypeptide A random coil is a polymer conformation where the monomer subunits are oriented randomly while still being bonded to adjacent units. ... In chemistry, chemical synthesis is purposeful execution of chemical reactions in order to get a product, or several products. ... A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... For other uses of this word, see nylon (disambiguation). ... This article refers collectively to all true hornets. ... Cockchafer (Melolontha melolontha) pupa Chrysalis redirects here: for other meanings see Chrysalis (disambiguation). ... For the band, see Adhesive (band). ...


Pairing

A (neutral-basic) B (acidic) Occurrence
keratin 1, keratin 2 keratin 9, keratin 10 stratum corneum, keratinocytes
keratin 3 keratin 12 cornea
keratin 4 keratin 13 stratified epithelium
keratin 5 keratin 14, keratin 15 stratified epithelium
keratin 6 keratin 16, keratin 17 squamous epithelium
keratin 7 keratin 19 ductal epithelia
keratin 8 keratin 18, keratin 20 simple epithelium

Keratin 1 is a member of the keratin family. ... There are very few or no other articles that link to this one. ... Keratin 9 is a type I cytokeratin. ... Keratin 10 is a type I cytokeratin. ... The stratum corneum (the horny layer) is the outermost layer of the epidermis (the outermost layer of the skin). ... The keratinocyte is the major cell type of the epidermis, making up about 90% of epidermal cells. ... Keratin 3 is a type II cytokeratin. ... Keratin 12 is a keratin found expressed in corneal epithelia. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... Keratin 4 is a type II cytokeratins. ... Keratin 13 is a type I cytokeratin, it is paired with keratin 4 and found in the suprabasal layers of non-cornified stratified epithelia. ... Stratified epithelium can refer to: Stratified squamous epithelium Stratified cuboidal epithelium Stratified columnar epithelia Category: ... Keratin 8 is a keratin protein often paired with keratin 14. ... Keratin 14 is a type I keratin. ... Keratin 15 is a type I cytokeratin. ... Stratified epithelium can refer to: Stratified squamous epithelium Stratified cuboidal epithelium Stratified columnar epithelia Category: ... There are very few or no other articles that link to this one. ... Keratin 16 is a type I cytokeratin. ... Keratin 17 is a type I cytokeratin. ... A comparison of squamous epithelia to other epithelial types In anatomy, squamous epithelium is an epithelium characterised by its most superficial layer consisting of flat, scalelike cells called squamous cells. ... Keratin 7 is a member of the keratin family. ... Keratin 19 is a type I cytokeratin. ... Keratin 8 is a keratin protein often paired with keratin 18. ... Keratin 18 is a type I cytokeratin. ... Keratin 20 is a type I cytokeratin. ...

Clinical significance

Some infectious fungi, such as those which cause athlete's foot and ringworm, feed on keratin. An infection is the detrimental colonization of a host organism by a foreign species. ... Subkingdom/Phyla Chytridiomycota Blastocladiomycota Neocallimastigomycota Glomeromycota Zygomycota Dikarya (inc. ... Athletes foot or Tinea pedis[1] is a parasitic fungal infection of the epidermis of the foot. ... This article is about the fungal infection. ...


Diseases caused by mutations in the keratin genes include

Epidermolysis bullosa simplex (EBS) is a disorder resulting from mutations in the genes encoding keratin 5 or 14. ... Epidermolytic hyperkeratosis, also known as bullous congenital ichthyosiform erythroderma or simply bullous congenital ichthyosiform erythroderma is a rare skin disease in the ichthyosis family affecting around 1 in 250,000 people. ... Steatocystoma multiplex is a congenital conditions resulting in multiple cysts on the body. ...

See also

Keratosis pilaris (KP) is a very common genetic follicular condition that is manifested by the appearance of rough bumps on the skin and hence colloquially referred to as chicken skin. It most often appears on the back and outer sides of the upper arms (though the lower arms can also... // Intermediate filaments (IFs) are important structural proteins which are located both in the cytoplasm and the nucleus. ... Cell adhesion in desmosomes A desmosome (also known as macula adherens (Latin for adhering spot ) is a cell structure specialized for cell-to-cell adhesion. ... Tinea versicolor or pityriasis versicolor is a common skin infection caused by the yeast Malassezia furfur or Pityrosporum ovale. ...

Additional images

References

  1. ^ Kreplak L, Doucet J, Dumas P, Briki F (2004). "New aspects of the alpha-helix to beta-sheet transition in stretched hard alpha-keratin fibers". Biophys J 87 (1): 640-7. PMID 15240497. 
  2. ^ http://www.amonline.net.au/spiders/toolkit/silk/structure.htm

External links


  Results from FactBites:
 
Keratin - Wikipedia, the free encyclopedia (1007 words)
Keratins are the main constituent of structures that grow from the skin: the α-keratins in the hair (including wool), horns, nails, claws and hooves of mammals; also the harder β-keratins in the scales and claws of reptiles, and their shells (tortoises), and in the feathers, beaks, and claws of birds.
Keratins contain a high proportion of the smallest of the 20 amino acids, glycine, whose "side group" is a single hydrogen atom; also the next smallest, alanine, with a small and uncharged methyl group.
Diseases caused by mutations in the keratin genes
Keratin - definition of Keratin in Encyclopedia (348 words)
Keratin is a protein used by numerous groups of animals as a structural element, and is a classic example of a fibrous protein.
Keratin is a tough insoluble protein found in the outer layer of the skin of human beings and many other animals.
In humans, the keratin family of proteins is divided into the soft epithelial keratins or cytokeratins and the hard hair keratins.
  More results at FactBites »

 
 

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