oilsandplants.com ~ Keratin KERATIN Keratins are a family of fibrous structural proteins ; which are extremely strong and are a major component in skin, hair, nails and teeth. The amino acids which combine to form keratin have several unique properties, and depending on the levels of the various amino acids, keratin can be inflexible and hard, like nails, or soft, as is the case with skin. Keratins are the main constituent of structures that grow from the skin: the a-keratins in the hair (including wool), horns, nails, claws and hooves of mammals the harder b-keratins found in nails and in the scales and claws of reptiles, their shells (chelonians, such as tortoise, turtle, terrapin), and in the feathers, beaks, claws of birds and quills of porcupines. (These keratins are formed primarily in beta sheets. However, beta sheets are also found in a-keratins.) Most of the keratin that people interact with is actually dead; hair, skin, and nails are all formed from dead cells which the body sheds as new cells push up from underneath.

If the dead cells are kept in good condition, they will serve as an insulating layer to protect the delicate new keratin below them. Keratin is difficult to dissolve, because it contains cysteine disulfide, which means that it is able to form disulfide bridges. These disulfide bridges create a helix shape that is extremely strong, as sulfur atoms bond to each other from across the helix, creating a fibrous matrix which is not readily soluble. Depending on how much cysteine disulfide keratin contains, the bond can be extremely strong to make hard cells like those found in hooves, or it can be softer to make flexible keratin like hair and skin. Because of the high levels of sulfur in keratin, when it is burned it emits a distinct sulfurous odor which some people find distasteful. Keratin is formed by keratinocytes, living cells which make up a large part of skin, hair, nails, and other keratin containing parts of the body. The cells slowly push their way upwards, eventually dying and forming a protective layer of cells. Thousands of these cells are shed every day, and the process can be accelerated by various medical conditions, such as psoriasis.

Damage to the external layer of keratin can cause skin, hair, and nails to look unhealthy or flaky. Hair and nails on humans especially tend to become dry and brittle, because the dead keratin is being pushed to great lengths. By eating foods like gelatin and keeping hair and nails moist, they can be grown out while still remaining healthy. In general, the thicker the layer of keratin, the healthier the hair or nail is, because the dead cells outside protect the living cells at the core. Keeping the external layer of keratin moisturized will also keep it healthy and prevent cracking and splitting, whether the keratin is forming the hooves of a horse of the skin of a human. THE INTEGUMENT AND ITS DERIVATIVES THE INTEGUMENT AND ITS DERIVATIVES Describe the components of the integument and their basic functions. Describe the structures that are produced from keratinization of the epidermis. Understand the formation and function of glands. Understand how the dermis contributes to the integument. Determine the composition of the various types of fish scales.

Understand the composition of teeth and be familiar with different types of tooth disposition, insertion and differentiation EPIDERMIS AND ITS DERIVATIVES The epidermis, derived from somatic ectoderm, is the exterior-most covering of the chordate body. It provides protection against the invasion of microorganisms, provides flexibility in motion, and seals in moisture. As will be seen, it also gives rise to a variety of differentiated structures such as feathers, hair, horns, claws, nails and glands. Begin by looking at a cross-section of Amphioxus (Branchiostoma) integument. Amphioxus possesses the simplest possible form of epidermis - a single layer of columnar epithelium covered by a thin film of cuticle. All true vertebrates, however, have developed a multi-layered epithelium. Note the simple, multicellular, epithelium of the lamprey, which has no scales. Fishes and amphibians have a mucus layer for bacterial and mechanical protection and to prevent drying on land. See frog skin.Terrestrial vertebrates have replaced the cuticle with keratin. See the snake skin.

Epidermal Derivatives of the Integument Keratin Structures New epidermal cells are formed continuously in the lower layers of the epidermis. In terrestrial vertebrates, new epidermal cells push more superficial ones to the stratum corneum, the outer-most epithelial layer. In the process of self-destruction, these exterior epidermal cells accumulate protein products called keratin. Keratinized or cornified skin serves to prevent water escape and to protect against friction and direct mechanical stimulation (e.g. calluses in humans). The production of all of the following structures involves keratinization: Epidermal Scales: a continuous layer of repetitious thickenings of the stratum corneum; you cannot dissect an individual epidermal scale out of the skin! These scales may be shed entirely (moulting) or in small flakes. Examine preserved specimen of snake skin and dried specimens of bird legs and feet. Claws and Talons: curved, laterally compressed keratinized projections from the tips of digits. See dried specimen of cat claws and bird talons. What are the possible functions of claws and talons? Hooves: enlarged keratinized plates found on the ends of ungulate digits.

Examine the hooves of pig and horse. Nails: keratinized epithelial cells are produced at the nail base and push the existing nail forward. They provide protection from mechanical injury and stabilize skin for better grasping. Found only in primates. Horns: a tough, cornified layer of the integument covers horns. Their core, however, is bone, which is of dermal origin. Horns are found in bovines (cattle, antelope, sheep, goats, bison, wildebeest). They are retained year-round and grow throughout the animal’s lifetime. Baleen: found in some whales, baleen is a series of keratinized plates that arise from oral epithelium. These sheets hang from the palate along its length and act as a sieve. See the display. Of what use would the sieve-like action of these baleen plates be? Beaks: epidermal structures, jaws are covered by keratinized sheaths in birds and turtles. Feathers: are believed to have evolved from reptilian scales. Columns of epidermal cells project into the skin initially to form an invagination called the feather follicle.

Later growth results in a projection out of the skin of a keratinized epidermal sheath with an inner feather shaft. These columns then separate and develop into barbs. Feather growth is initiated by dermal papillae, which die in the grown feather to form feather pulp. Examine the dried specimens. Note the quill (calamus), which attaches to the body and extends as a rachis. From the rachis project many veins with barbs and barbules to hold them together. Hair: just as in feathers, there is an initial ingrowth of epidermal cells to form the hair follicle, followed by an outward growth of keratinized cells to form the hair shaft. Dermal papillae cells of the outer edge die and form the core substance of hair follicles. Note the similarities between hair and feathers both in development and in general anatomy. They both possess dermal papillae, shafts, an inner pulp and columns of specialized keratinized cells. Hair is characteristic of mammals. Which is the living layer of the epidermis in the human scalp? Which is the non-living layer of the epidermis? What is the primary function of each epidermal layer?

Glands Specialized to secrete specific products (oil, sweat, milk, etc.), these structures are derived by an infolding of the epidermis. In many cases they retain a connection to the stratum corneum whereby their secretions can be released at the skin surface. What do you think is responsible for the slimy feeling of fish skin? Sketch and label the glands of the frog as seen in the frog integument slide (cross-section). Sketch and label the human scalp cross-section with oil (sebaceous) and sweat glands. THE DERMIS AND ITS DERIVATIVES The dermis is generally much thicker than the epidermis and lies more deeply. It is made of a fibrous mass of connective tissue (collagen) and is of mesodermal origin. It may directly produce dermal (membrane) bone. The dermis is important in defence against injury and in the maintenance of body heat. Deeper regions of the dermis often contain fatty deposits, smooth muscle, blood vessels and nerves. Chromatophore cells are sometimes epidermal, but usually dermal in origin.

They secrete melanin, which can be passed to the stratum corneum of skin and to hair shafts to produce colour and block harmful sunlight. Dermal Bone Once present in some extinct fish - Ostracoderms had a complete head shield, while Placoderms had a broken head shield and body armour. Now dermal bone is present in turtle dermal bone, antlers, and in the dermal armour of armadillo. In antlers the velvet is epidermal in origin and shapes and provides blood to the dermal bone. Once grown, the velvet is shed and only the bone remains. Antlers are found in deer, elk, moose and their relatives, often only in males. They are shed annually. In most modern vertebrates, dermal bone (membrane bone) is formed from embryonic mesenchyme by intramembranous ossification, and contributes to the skull and skeleton, rather than being manifested externally. An exception is teeth, which are partly derived from dermal bone. Fish Scales Fish scales are also called dermal scales since they are derived mainly from the dermis.

1)Cosmoid Scales: Found in Placoderms (extinct) as plates, and also typical of the Lobe Finned Fishes or Sarcopterygii, (Choanichthyes). Extinct fish had scales of enamel, cosmine and bone with pulp cavities. Modern ones, like Coelocanth and the lung fish have calcified fibers so this type of scale is almost extinct. No specimens available. 2)Ganoid Scales: See bioplastic mounts, slides, the plates of sturgeon, called scutes, and the scales of the gar pike on display. Made of multi-layered enamel called ganoin over lamellar bone. Primitive (now extinct) species also had a cosmine layer and vascular bone with pulp, but these were lost in modern day examples. 3)Placoid Scales: See bioplastic mounts and dogfish slides. Made of enamel (epidermal) and the dermal derivatives, dentine and bone with a pulp core. They are typical of cartilaginous fishes. Placoid scales are responsible for the rough feeling of dogfish skin. 4) Teleost (bony fish) scales These are thin scales of dermal bone.

They have a thin covering of epidermal tissue over them. It is derived by reduction (loss) of parts of a ganoid scale. There are two types depending on their shape. 4a) Cycloid Scales: See bioplastic mounts and slides. A round ended scale. 4b) Ctenoid Scales: See bioplastic mounts and slides. A comb shaped end is characteristic of this scale type. Referring to the bioplastic mount and slides, make a sketch of the placoid, ganoid, cycloid and ctenoid scales. This sketch is for your own reference so do not copy the drawings but draw what you see under the microscope. TEETH Teeth are composed of three main parts. Enamel, the hardest substance in the body, covers the tooth surface. It is epidermal in origin. Ganoin is a form of enamel. Dentin is similar to bone in structure but is harder. It is located beneath the enamel and forms the walls of the third component of teeth, the pulp cavity. These are of dermal origin. Cosmine is a form of dentin. Dermal bone called cementum is also present in mammalian teeth.

Teeth are used to catch and hold prey, to crush hard shells and, in some higher vertebrates, to carry out mechanical digestion of food in the mouth. How does breaking of food into smaller pieces improve its digestion? Examine the shark teeth on demonstration. Note that mollusk-eating sharks have blunt teeth, while others have a cutting edge. Despite such variations, the scales formed on dogfish skin and the teeth found in its mouth are both made of enamel, dentin and bone with a pulp core, i.e. shark teeth are modified placoid scales. Draw both the cross-section and the whole flat-mount of dogfish skin. Teeth of higher vertebrates are thought to have evolved from bony dermal scales similar to dogfish placoid scales. They have a complex embryonic origin involving both the epidermis and the dermis. Interestingly, their development bears some resemblance to that of hair and feathers. Mesenchyme cells collect in the dermis to form dermal papillae, which are instrumental in the production of dentin and go on to form the pulp of the tooth. Enamel is produced by the epidermis. The tooth in mammals is held in place by cement, which is a non-vascular form of bone.

To compare the various types of dermal scales with teeth, fill in the chart in your lab manual indicating the presence (+) or absence (-) of the indicated substances. TOOTH CHARACTERIZATION Tooth Position (where are they found?) 1) Fishes Teeth, or dermal structures, which are tooth-like, may be found wherever ectoderm occurs in the mouth area. For this reason teeth can occur outside the jaws as in the pharyngeal teeth on the bony elements of the branchial bars, or outside the buccal cavity as teeth in the sawfish. See Amia, pike and sawfish. How does this relate to deuterostome development in vertebrates (recall the development of the mouth and anus)? 2) Amphibians Teeth occur mainly on the jawbones, with some occurrence on the palate. Examine the skulls of frog (Anurans) and the salamander Necturus (Urodeles) on demonstration. 3) Reptiles A few reptiles still have teeth on their palate to hold their prey, but most teeth are on the jawbones. 4) Birds A few birds have teeth on their beaks, but teeth are absent in most birds.

5) Mammals Teeth occur only on the jawbones, i.e. on the dentary, premaxilla and maxilla. What general trend in tooth location do you observe across the vertebrate phyla? Tooth Insertion (how they are attached). There are three methods of tooth insertion. Examine the demonstration material and identify the following methods of insertion: 1)Acrodont (acro=end) The teeth are fused by their bases to the outer surface of the jaw. This condition occurs in most Teleosts (bony fish) and can be also seen in the sharks. The teeth are not firmly rooted and are easily lost and replaced. Teeth that are continually replaced are called polyphyodont (poly=many). 2)Pleurodont (pleur=side) The teeth are fused on one side to the inner surface of the jaw. This occurs in the salamander, Necturus, frogs, and in the lizards. Most birds have no teeth but mergansers, Peking duck and a few others have pleurodont teeth. Pleurodont teeth are usually polyphyodont. What are reasons for the loss of teeth in most birds? How do they compensate for this loss?

3)Thecodont (theca=cup) The teeth are placed on the crown of the jaw in a socket. A tooth may have a single root, as in the alligators, or several roots, as in the molars of mammals. What general trend in tooth insertion do you observe across the vertebrate phyla? Most thecodont vertebrates replace their teeth only once in their lifetime. Describe some possible reasons for this. What advantage(s) do acrodonts have over pleurodonts and thecodonts? What disadvantage(s)? C) Tooth Differentiation (how they differ) The shape of the teeth in the fishes, amphibia and reptiles is relatively constant in any one group. Functional adaptations occur in size, and in specialization such as poison ducts in the fangs of snakes. Study the demonstration material in the above groups and notice the similarity in shape - called the Isodont or Homodont (iso/homo = equal) condition. Dentition in mammals is generally Heterodont (hetero=different). The teeth are modified in shape and size to serve specialized functions. Study this modification in the wolf skull.

Notice incisors (cutting), canines (piercing), premolars (grinding) and carnassials (shearing), and molars (crushing). Examine the general demonstration of mammalian teeth. Notice the adaptations are correlated with food habits. Compare the insectivores, herbivores, carnivores and omnivores. Examine the shrew and mole as examples of insectivores, which eat insects and other small invertebrates. Most of the teeth are generalized and little differentiation has taken place. Why would insectivores need such long and sharp incisors? Examine upper and lower jaws of the herbivores, which feed on grasses and other vegetation. Note the differences, a large gap, the diastema (=internal) and often a horny upper pad - check the grazers (horse, deer, ox), and the gnawers (rabbit, beaver). Why do herbivores have such long jaws formed by the diastema? Why are the molars and pre-molars so corrugated (alternating ridges and furrows) in herbivores?

In the carnivores, which feed mainly on herbivores, note the specialized long and sharp canine teeth for biting and piercing, and the last premolar of upper jaw and first molar of lower jaw, which have been modified as carnassials used for cutting. Within the group notice variations of teeth used for cutting, piercing, incising and gripping. How do you think the carnassials work? (Hint: look at which surfaces touch each other) Examine the omnivore dentition (pigs, bears, humans) and compare with carnivores, herbivores and insectivores. Bears are omnivores, eating whatever is available. Note, however, that their overall tooth differentiation resembles that of carnivores. There is a discrepancy here. Why do you think this is so? Anatomy and Physiology of Animals/The Skin - Wikibooks, open books for an open world Anatomy and Physiology of Animals/The Skin From Wikibooks, open books for an open world Jump to: navigation , search original image by Fran-cis-ca cc by The skin is the first of the eleven body systems to be described. Each chapter from now on will cover one body system.

The skin, sometimes known as the Integumentary System is, in fact, the largest organ of the body. It has a complex structure, being composed of many different tissues. It performs many functions that are important in maintaining homeostasis in the body. Probably the most important of these functions is the control of body temperature. The skin also protects the body from physical damage and bacterial invasion. The skin has an array of sense organs which sense the external environment, and also cells which can make vitamin D in sunlight. The skin is one of the first systems affected when an animal becomes sick so it is important for anyone working with animals to have a sound knowledge of the structure and functioning of the skin so they can quickly recognise signs of disease.

Contents After completing this section, you should know: the general structure of the skin the function of the keratin deposited in the epidermis the structure and function of keratin skin structures including calluses, scales, nails, claws, hoofs and horns that antlers are not made either of keratin or in the epidermis the structure of hairs the structure of the different types of feathers and the function of preening the general structure and function of sweat, scent, preen and mammary glands the basic functions of the skin in sensing stimuli, temperature control and production of vitamin D the mechanisms by which the skin regulates body temperature The Skin[ edit ] Skin comes in all kinds of textures and forms. There is the dry warty skin of toads and crocodiles, the wet slimy skin of fish and frogs, the hard shell of tortoises and the soft supple skin of snakes and humans. Mammalian skin is covered with hair, that of birds with feathers, and fish and reptiles have scales. Pigment in the skin, hairs or feathers can make the outer surface almost any colour of the rainbow. Skin is one of the largest organs of the body, making up 6-8% of the total body weight.

It consists of two distinct layers. The top layer is called the epidermis and under that is the dermis' The epidermis is the layer that bubbles up when we have a blister and as we know from this experience, it has no blood or nerves in it. The cells at the base of the epidermis continually divide and push the cells above them upwards. As these cells move up they die and become the dry flaky scales that fall off the skin surface. The cells in the epidermis die because a special protein called keratin is deposited in them. Keratin is an extremely important substance for it makes the skin waterproof. Without it land vertebrates like reptiles, birds and mammals would, like frogs, be able to survive only in damp places. Skin Structures Made Of Keratin[ edit ] Claws, Nails and Hoofs[ edit ] Reptiles, birds and mammals all have nails or claws on the ends of their toes. They protect the end of the toe and may be used for grasping, grooming, digging or in defense. They are continually worn away and grow continuously from a growth layer at their base (see diagram 5.2).

Diagram 5.2 - A carnivore’s claw Hoofs are found in sheep, cows, horses etc. otherwise known as ungulate mammals. These are animals that have lost toes in the process of evolution and walk on the “nails” of the remaining toes. The hoof is a cylinder of horny material that surrounds and protects the tip of the toe (see diagram 5.3). Diagram 5.3 - A horse’s hoof Horns And Antlers[ edit ] True horns are made of keratin and are found in sheep, goats and cattle. They are never branched and, once grown, are never shed. They consist of a core of bone arising in the dermis of the skin and are fused with the skull. The horn itself forms as a hollow cone-shaped sheath around the bone (see diagram 5.4). Diagram 5.4 - A horn The antlers of male deer have quite a different structure. They are not formed in the epidermis and do not consist of keratin but are entirely of bone. They are shed each year and are often branched, especially in older animals. When growing they are covered in skin called velvet that forms the bone.

Later the velvet is shed to leave the bony antler. The velvet is often removed artificially to be sold in Asia as a traditional medicine (see diagram 5.5). Diagram 5.5 - A deer antler Other animals have projections on their heads that are not true horns either. The horns on the head of giraffes are made of bone covered with skin and hair, and the ‘horn’ of a rhinoceros is made of modified and fused hair-like structures. Hair[ edit ] Hair is also made of keratin and develops in the epidermis. It covers the body of most mammals where it acts as an insulator and helps to regulate the temperature of the body (see below). The colour in hairs is formed from the same pigment, melanin that colours the skin. Coat colour may help camouflage animals and sometimes acts to attract the opposite sex. Diagram 5.6 - A hair Hairs lie in a follicle and grow from a root that is well supplied with blood vessels. The hair itself consists of layers of dead keratin - containing cells and usually lies at a slant in the skin.

A small bundle of smooth muscle fibres (the hair erector muscle) is attached to the side of each hair and when this contracts the hair stands on end. This increases the insulating power of the coat and is also used by some animals to make them seem larger when confronted by a foe or a competitor(see diagram 5.6). The whiskers of cats and the spines of hedgehogs are examples of special types of hairs. Feathers[ edit ] The lightness and stiffness of keratin is also a key to bird flight. In the form of feathers it provides the large airfoils necessary for flapping and gliding flight. In another form, the light fluffy down feathers,also made of keratin, are some of the best natural insulators known. This superior insulation is necessary to help maintain the high body temperatures of birds. Diagram 5.7 - A Contour Feather Countour feathers are large feathers that cover the body, wings and tail. They have an expanded vane that provides the smooth, continuous surface that is required for effective flight. This surface is formed by barbs that extend out from the central shaft.

If you look carefully at a feather you can see that on either side of each barb are thousands of barbules that lock together by a complex system of hooks and notches. if this arrangement becomes disrupted, the bird uses its beak to draw the barbs and barbules together again in an action known as preening (see diagram 5.7). Diagram 5.8 - A Down Feather Diagram 5.9 - A Pin Feather Down feathers are the only feathers covering a chick and form the main insulation layer under the contour feathers of the adult. They have no shaft but consist of a spray of simple, slender branches (see diagram 5.8). Pin feathers have a slender hair-like shaft often with a tiny tuft of barbs on the end. They are found between the other feathers and help tell a bird how its feathers are lying (see diagram 5.9). Skin Glands[ edit ] Glands are organs that produce and secrete fluids. They are usually divided into two groups depending upon whether or not they have channels or ducts to carry their products away. Glands with ducts are called exocrine glands and include the glands found in the skin as well as the glands that produce digestive enzymes in the gut.

Endocrine glands have no ducts and release their products (hormones) directly into the blood stream. The pituitary and adrenal glands are examples of endocrine glands. Most vertebrates have exocrine glands in the skin that produce a variety of secretions. The slime on the skin of fish and frogs is mucus produced by skin glands and some fish and frogs also produce poison from modified glands. In fact the skin glands of some frogs produce the most poisonous chemicals known. Reptiles and birds have a dry skin with few glands. The preen gland, situated near the base of the bird’s tail, produces oil to help keep the feathers in good condition. Mammals have an array of different skin glands. These include the wax producing, sweat, sebaceous and mammary glands. Wax producing glands are found in the ears. Sebaceous glands secrete an oily secretion into the hair follicle. This secretion, known as sebum, keeps the hair supple and helps prevent the growth of bacteria (see diagram 5.6). Sweat glands consist of a coiled tube and a duct leading onto the skin surface.

Their appearance when examined under the microscope inspired one of the first scientists to observe them to call them “fairies’ intestines” (see diagram 5.1). Sweat contains salt and waste products like urea and the evaporation of sweat on the skin surface is one of the major mechanisms for cooling the body of many mammals. Horses can sweat up to 30 litres of fluid a day during active exercise, but cats and dogs have few sweat glands and must cool themselves by panting. Scent in the sweat of many animals is used to mark territory or attract the opposite sex. Mammary glands are only present in mammals. They are thought to be modified sebaceous glands and are present in both sexes but are rarely active in males (see diagram 5.10). The number of glands varies from species to species. They open to the surface in well-developed nipples. Milk contains proteins, sugars, fats and salts, although the exact composition varies from one species to another. Diagram 5.10 - A Mammary Gland The Skin And Sun[ edit ] A moderate amount of UV in sunlight is necessary for the skin to form vitamin D.

This vitamin prevents bone disorders like rickets to which animals reared indoors are susceptible. Excessive exposure to the UV in sunlight can be damaging and the pigment melanin, deposited in cells at the base of the epidermis, helps to protect the underlying layers of the skin from this damage. Melanin also colours the skin and variations in the amount of melanin produces colours from pale yellow to black. Sunburn And Skin Cancer[ edit ] Excess exposure to the sun can cause sunburn. This is common in humans, but light skinned animals like cats and pigs can also be sunburned, especially on the ears. Skin cancer can also result from excessive exposure to the sun. As holes in the ozone layer increase exposure to the sun’s UV rays, so too does the rate of skin cancer in humans and animals. The Dermis[ edit ] The underlying layer of the skin, known as the dermis, is much thicker but much more uniform in structure than the epidermis (see diagram 5.1). It is composed of loose connective tissue with a felted mass of collagen and elastic fibres. It is this part of the skin of cattle and pigs etc. that becomes commercial leather when treated,.

The dermis is well supplied with blood vessels, so cuts and burns that penetrate down into the dermis will bleed or cause serious fluid loss. There are also numerous nerve endings and touch receptors in the dermis because, of course, the skin is sensitive to touch, pain and temperature. When looking at a section of the skin under the microscope you can see hair follicles, sweat and sebaceous glands dipping down into the dermis. However, these structures do not originate in the dermis but are derived from the epidermis. In the lower levels of the dermis is a layer of fat or adipose tissue (see diagram 5.1). This acts as an energy store and is an excellent insulator especially in mammals like whales with little hair. The Skin And Temperature Regulation[ edit ] Vertebrates can be divided into two groups depending on whether or not they control their internal temperature. Amphibia (frogs) and reptiles are said to be”cold blooded” (poikilothermic) because their body temperature approximately follows that of the environment.

Birds and mammals are said to be warm blooded (homoiothermic) because they can maintain a roughly constant body temperature despite changes in the temperature of the environment. Heat is produced by the biochemical reactions of the body (especially in the liver) and by muscle contraction. Most of the heat loss from the body occurs via the skin. It is therefore not surprising that many of the mechanisms for controlling the temperature of the body operate here. Reduction Of Heat Loss[ edit ] When an animal is in a cold environment and needs to reduce heat loss the erector muscles contract causing the hair or feathers to rise up and increase the layer of insulating air trapped by them (see diagram 5.11a). Diagram 5.11a) Hair muscle relaxed...............Diagram 5.11b) Hair muscle contracted Heat loss from the skin surface can also be reduced by the contraction of the abundant blood vessels that lie in the dermis. This takes blood flow to deeper levels, so reducing heat loss and causing pale skin (see diagram 5.12a). Diagram 5.12a) Reduction of heat loss by skin Shivering caused by twitching muscles produces heat that also helps raise the body temperature.

Increase Of Heat Loss[ edit ] There are two main mechanisms used by animals to increase the amount of heat lost from the skin when they are in a hot environment or high levels of activity are increasing internal heat production. The first is the expansion of the blood vessels in the dermis so blood flows near the skin surface and heat loss to the environment can take place. The second is by the production of sweat from the sweat glands (see diagram 5.12b). The evaporation of this liquid on the skin surface produces a cooling effect. The mechanisms for regulating body temperature are under the control of a small region of the brain called the hypothalamus. This acts like a thermostat. Diagram 5.12b) - Increase of heat loss by skin Heat Loss And Body Size[ edit ] The amount of heat that can be lost from the surface of the body is related to the area of skin an animal has in relation to the total volume of its body. Small animals like mice have a very large skin area compared to their total volume. This means they tend to loose large amounts of heat and have difficulty keeping warm in cold weather. They may need to keep active just to maintain their body temperature or may hibernate to avoid the problem.

Large animals like elephants have the opposite problem. They have only a relatively small skin area in relation to their total volume and may have trouble keeping cool. This is one reason that these large animals tend to have sparse coverings of hair. Summary[ edit ] Skin consists of two layers: the thin epidermis and under it the thicker dermis. The Epidermis is formed by the division of base cells that push those above them towards the surface where they die and are shed. Keratin, a protein, is deposited in the epidermal cells. It makes skin waterproof. Various skin structures formed in the epidermis are made of keratin. These include: claws, nails, hoofs, horn, hair and feathers. Various Exocrine Glands (with ducts) formed in the epidermis include sweat, sebaceous, and mammary glands. Melanin deposited in cells at the base of the epidermis protects deeper cells from the harmful effects of the sun. The Dermis is composed of loose connective tissue and is well supplied with blood. Beneath the dermis is insulating adipose tissue. Body Temperature is controlled by: sweat, hair erection, dilation and contraction of dermal capillaries and shivering.

A whale's life, inscribed in baleen | Science A whale's life, inscribed in baleen Rebecca Kessler * Vol. 350, Issue 6266, pp. 1300-1301 DOI: 10.1126/science.350.6266.1300 View Full Text Summary In 2004, a collision with a ship cut short the life of an endangered North Atlantic right whale named Stumpy. Many lamented her death, but Stumpy's demise could ultimately help other whales. Researchers are using her tough, hairlike baleen to develop a new method of reconstructing a whale's life story—much as scientists use growth rings to reveal a tree's past. The nascent technique could make it easier to study, and perhaps protect, whales. Deriving whale biographies from baleen is just one concept to be discussed next week at the 21st Biennial Conference on the Biology of Marine Mammals in San Francisco, California. Some 3000 researchers will share insights into some of the world's most charismatic creatures, including first-time audio recordings of rare species and updates on struggling populations.

They'll also discuss novel ways of assessing the health and physiology of free-swimming mammals that can be hard to study in the wild. That's where the work involving Stumpy—and a second right whale named Staccato—will come in. Over the past decade or so, wildlife researchers have been figuring out how to pry life history information out of tissues based on keratin, the fibrous protein found in nails, hair, feathers, horns, claws, hooves, and skin. Now, they're focusing on the keratin in baleen. ↵ * Rebecca Kessler is a journalist in Providence. Structural Proteins Structural Protein Measured in terms of their total mass, the largest class is the structural one. Structural proteins are fibrous proteins. The most familiar of the fibrous proteins are probably the keratins, which form the protective covering of all land vertebrates: skin, fur, hair, wool, claws, nails, hooves, horns, scales, beaks and feathers. Equally widespread, if less visible, are the actin and myosin proteins of muscle tissue. Another group of fibrous structural proteins are the silks and insect fibers.

In addition, there are the collagens of tendons and hides, which form connective ligaments within the body and give extra support to the skin where needed. Keratins There is a great variety in the structures of the various fibrous proteins, more than we can look at in this lesson. But let's take a look at one common example, the keratin structure of hair, which is shown in example 7 in your workbook. The basic unit of hair is a long strand of protein chain which forms into an alpha helical secondary structure. Three of these alpha-helical lengths of protein wind around each other to form a structure called a protofibril. In turn, a microfibril is assembled from eleven protofibrils arranged in a way that involves nine protofibrils wound around two protofibrils. Hundreds of microfibrils are then packed together with a sort of protein glue to form a macrofibril. These macrofibrils are, in turn, packed within the body of a dead hair cell. A typical hair fiber is about ten hair cells in diameter. A typical growth rate for human hair is about one half of an inch per month.

This requires that the hair follicle produce approximately ten turns of alpha helical protein every second. Ten turns, by the way, is about thirty-six amino acids. The protein strands within hair and other alpha-keratins are crosslinked to some extent by covalent bonds between cysteine residues to form disulfide bonds. The more such disulfide bonds there are between the strands, the more rigid the protein becomes as a whole. The alpha keratins can be classed as "soft" or "hard" according to their sulfur content, which is to say, the relative number of cysteines in the polypeptide chains. The low-sulfur keratins of skin and callous are much more flexible than the high-sulfur, hard keratins of horns, claws and hooves. Cysteine-Cystine Transformation The basic principle of the permanent wave process for hair involves breaking the existing disulfide bonds between a-helices and then reforming new disulfide bonds after the hair fibers have been shaped and rearranged by the hair stylist. A reducing agent is first applied to the hair to break the disulfide bridges.

The hair is then arranged into the desired shape and an oxidizing agent applied to cause reformation of the disulfide bonds. A "permanent" is really only permanent for the portion of the hair that was processed, and it lasts until new, untreated keratin replaces it. Keratin - New World Encyclopedia Keratin Next (Kermit Roosevelt, Jr.) Microscopy of keratin filaments inside cells. Keratin is any one of the family of tough and insoluble fibrous structural proteins that form the chief, hard, nonmineralized structural component of hair , wool , horns , nails , claws, hooves, and other vertebrate tissues, as well as part of various invertebrate structures. Keratins are rivaled as biological materials in toughness only by chitin . Keratins are present in all epithelial cells, both those covering the external surfaces of organisms and those on internal surfaces, such as the lining of the digestive tract . Keratins aid the epithelial cells in maintaining their connected integrity, as the keratins typically span the full interior width of a cell and are connected indirectly to keratins in adjoining cells through cell-to-cell junctions called desmosomes.

The horn, hooves, nails, hair, and other keratin-based hard, tough materials growing on animals are produced by epithelial cells adapted to growing an abundance of keratin and then dying as individual cells while leaving the keratin to help form a structure valuable to the whole animal. Keratin's characteristic toughness and resilience depend on its amino acid composition and sequence and the particular protein folding that results. In particular, the prevalence in Keratin of the sulfur -containing amino acid cysteine , with its ability to form strong covalent chemical bonds between sulfur atoms (disulfide bridge), helps confer strength and rigidity. The complexity involved in just this one type of protein is remarkable, and yet it is formed by a vast diversity of living organisms. There are various types of keratins within a single animal . Keratin is nutritionally useless to humans, since it is not hydrolyzed by digestive enzymes , but it can be used as fertilizer, being slowly broken down by bacteria (Bender and Bender 2005). Contents Uses in animals Keratins are the chief constituent of structures that grow from the skin of vertebrates .

These structures include: Among mammals , the hair (including wool), horns, nails, claws, corns, and hooves, which are made primarily of α-keratins Among reptiles , the scales , claws, and, in the chelonians, such as tortoise , turtle , terrapin, the shells, which are made primarily of β-keratins Among birds , the feathers , beaks, and claws, which are made primarily of β-keratins The α-keratins are formed primarily as helical fibers, while the β-keratins are formed primarily in beta sheets. Some beta sheets are also found in α-keratins (Kreplak et al. 2004). For example, hair, a filamentous outgrowth from the skin that is found only on mammals, involves fibers comprising nonliving cells whose primary component is the protein keratin, a long chain (polymer) of amino acids that naturally forms an α-helix fiber and subsequently winds two of the α-helix fibers together to form a much stronger "coiled coil" fiber characteristic of α-keratin.

The keratinized cells arise from cell division in the hair matrix at the base of a hair follicle and are tightly packed together. Keratin (high molecular weight) in bile duct cell and oval cells of mouse liver Keratins also are a principle part of the cells in the tooth enamel of mammals and the baleen plates of filter-feeding whales . Although it is now difficult to be certain, the prevailing view among paleontologists is that the scales, claws, beaks, and some protective armor of dinosaurs most likely were composed of a type of keratin. In Crossopterygian fish, the outer layer of cosmoid scales was keratin. Among the invertebrates , arthropods such as crustaceans often have parts of their armor or exoskeleton made of keratin, sometimes in combination with chitin , which is a hard, semitransparent polysaccharide that is the main component of the shells of crustaceans, such as crabs , lobsters , and shrimp .

In arthropods, however, chitin is frequently modified by being embedded in a hardened proteinaceous matrix of keratin, giving a more rigid exoskeleton, than seen, for example, in the use of chitin in the soft, more pliable body wall of a caterpillar . Keratins also can be integrated in the chitinophosphatic material that makes up the shell and setae (bristles) in many brachiopods . Keratins also are found in the gastrointestinal tracts of many animals, including roundworms (who also have an outer layer made of keratin). Molecular biology and biochemistry The properties that make structural proteins like keratins useful depend on their supermolecular aggregation, i.e., their pattern of protein ( polypeptide strand) folding. The properties of collectives of protein strands 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 the disulfide bridges, are central to the architecture and aggregation of keratins. Disulfide bridges Cysteine , an amino acid with the thiol functional group -SH.

Cystine, showing a disulfide bond (-S-S-) joining two cysteine residues. Keratins have large amounts of the sulfur -containing amino acid cysteine , which is characterized by the thiol functional group, -SH, comprising a sulfur atom and a hydrogen atom. In the keratin polymer, which is originally extremely flexible, the thiol groups tend to pair up and, through oxidation , form a covalent sulfur-sulfur, that is, disulfide, bond with the loss of two protons and two electrons. A disulfide bond, also called a SS-bond or disulfide bridge, achieves an overall connectivity represented by C-S-S-C, in which "C" represents the immediate next carbon atom and all the remainder of the associated amino acid. Expressed more formally, when cysteine is oxidized it can form cystine, which is two cysteine residues (cys) joined by a disulfide bond (cys-S-S-cys) between the -SH group. Disulfide bridges confer additional strength and rigidity by permanent, thermally-stable crosslinking—a role sulfur bridges also play in vulcanized rubber .

Human hair is approximately 14 percent 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. 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 wound together into superhelical or coiled-coil 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. Glycine and alanine The general structure of an amino acid molecule. For glycine, the simplest amino acid, R in the figure is replaced by -H. For alanine, R is replaced by the methyl group -CH3.

The amino group (-NH2) is on the left and the carboxyl group (-COOH) is on the right. Keratins contain a high proportion of the smallest of the 20 amino acids , glycine , whose "side group" is a single hydrogen atom. They also contain a high proportion of the next smallest, alanine , whose functional side group is the small and noncharged methyl group. In the case of β-sheets, this high proportion of simple and neutral side groups allows sterically-unhindered hydrogen bonding between the amino and carboxyl groups of peptide bonds on adjacent protein chains, facilitating their close alignment and strong bonding. Fibrous keratin molecules can twist around each other to form double-wound helical intermediate filaments. The triple helix of the (unrelated) structural protein collagen , found in skin, cartilage , and bone , likewise has a high percentage of glycine, as does the connective tissue protein elastin, which also has a high percentage of alanine.

Spider silk fibroin, considered a β-keratin, can have glycine and alanine as 75–80 percent of its total amino acids, with an additional 10–15 percent being serine, and the rest being amino acids that have bulky side groups. The chains are antiparallel, with an alternating C → N orientation (Ophardt 2003). 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. 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. 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 (such as dandruff). 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 molt and regenerate. The constituent proteins may be phylogenetically homologous but differ somewhat in chemical structure and super molecular 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. Another example of keratinzed cells are nails . According to Levit and Boissy (2001), the nail plate is composed of "closely packed, fully keratinized, multilayered lamellae of cornified cells" (Levit and Boissy 2001). Essentially, cells in the epidermis contain a structural matrix of keratin.

The nail matrix cells differentiate and create the nail plate by flattening, broadening, and by nuclear fragmentation, with an accumulation of cytoplasmic microfibrils (Levit and Boissy 2001). As skin cells become cornified, and the nucleus and cytoplasmic organelles disappear and metabolism ceases, the cells become fully keratinized. Hard structures are formed by intercellular cementing of fibers formed from the dead, cornified cells.The keratins in the nail plate are believed to be held in place by surrounding globular matrix proteins with a high concentration of disulfide bonds between cystine (rather than by means of calcium, as in bones), creating the rigid structure (Levit and Boissy 2001). 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. 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 micrometers (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 (AMO 2002). 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.

Medical significance Some infectious fungi , such as those that cause athlete's foot, ringworm, and the amphibian disease chytridiomycosis (caused by the chytrid fungus, Batrachochytrium dendrobatidis), feed on keratin. Diseases caused by mutations in the keratin genes include: Epidermolysis bullosa simplex Epidermolytic hyperkeratosis Steatocystoma multiplex Although keratin is insoluble and is not easily hydrolysed by digestive enzymes (Bender and Bender 2005), it can be used for coating pills designed to be dissolved when in the intestine . A supplement for ruminants also is made from steamed feather meal (Bender and Bender 2005). References Australian Museum Online. 2002. Spiders: Silk structure. Australian Museum Online. Retrieved May 23,2008. Bender, D. A., and A. E. Bender. 2005. A Dictionary of Food and Nutrition. New York: Oxford University Press. ISBN 0198609612 .

Keratin - The Full Wiki The Full Wiki Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles . Related top topics the casque of the Tarictic hornbill is hollow and made of keratin ? the casque of the Tarictic Hornbill is hollow and made of keratin ? Not to be confused with kerogen , carotene , creatine , or keratan sulphate . Microscopy of keratin filaments inside cells. Keratin refers to a family of fibrous structural proteins . Keratin is an intermediate filament ; when assembled in bundles, it is tough and insoluble forming hard, un mineralized structures found in reptiles , birds , amphibians , and mammals . They are rivalled as biological matter in toughness only by chitin . There are various types of keratins within a single bioform. The outer layer of hair is also made of keratin. Notice that if you bend a piece of hair, it does does not break.

Contents the α-keratins in the hair (including wool ), horns , nails , claws and hooves of mammals the harder β-keratins found in nails and in the scales and claws of reptiles , their shells ( chelonians , such as tortoise , turtle , terrapin ), and in the feathers , beaks , claws of birds and quills of porcupines. [1] (These keratins are formed primarily in beta sheets . However, beta sheets are also found in α-keratins.) [2] Arthropods such as crustaceans often have parts of their armor or exoskeleton made of keratin, some times in combination with chitin . The baleen plates of filter-feeding whales are made of keratin. It can be integrated in the chitinophosphatic matter that composes the shell and setae in many brachiopods . Keratin is also found in the gastrointestinal tracts of many bioforms, including roundworms (which also have outer layers of keratin).

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 keratin.[citation needed] Cornification It used to be thought that keratins were separable into 'hard' and 'soft,' or ' cytokeratins ' and 'other keratins', but those designations are now understood to be incorrect. A new nomenclature adopted in 2006 to describe keratins takes this into account [3] . Keratins are intermediate filaments . Like all intermediate filaments, keratin proteins form filamentous polymers in a series of assembly steps beginning with dimerization; dimers assemble into tetramers and octamers and eventually, the current hypothesis holds, into unit-length-filaments (ULF) capable of annealing end-to-end into long filaments. During the process of epithelial differentiation , cells become cornified as keratin protein is incorporated into longer keratin intermediate filaments. Eventually the nucleus and cytoplasmic organelles disappear, metabolism ceases and cells under go a programmed death as they become fully keratinized.

In many other cells types, such as dermis , keratin functions in the cytoplasm to mechanically stabilize the cell against physical stress. It does this through connections to desmosomes , cell-cell junctional plaques, and hemidesmosomes , cell-basement membrane adhesive structures. 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 ). 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 super molecular 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.

Molecular biology and biochemistry The usefulness of keratins depends 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. Glycine and alanine Keratins contain a high proportion of the two smallest amino acids: glycine (whose " side group " is a single hydrogen atom ) and 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. 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. [4] A preponderance of amino acids with small, nonreactive side groups is characteristic for structural proteins, for which H-bonded close packing is more important than chemical specificity . 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 in solubility of keratins, except in dissociating or reducing agents.

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. 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. 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 . [5] 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. Pairing Keratin | Define Keratin at Dictionary.com keratin noun 1. a scleroprotein or albuminoid substance, found in the dead outer skin layer, and in horn, hair, feathers, hoofs, nails, claws, bills, etc. Origin of keratin Examples from the Web for keratin Expand The Nuttall Encyclopaedia Edited by Rev.

James Wood British Dictionary definitions for keratin Expand noun 1. a fibrous protein that occurs in the outer layer of the skin and in hair, nails, feathers, hooves, etc Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for keratin Expand n. basic substance of horns, nails, feathers, etc., 1847, from Greek keras (genitive keratos) "horn" (see kerato- ) + chemical suffix -in (2).

Online Etymology Dictionary, © 2010 Douglas Harper Keratin Facts for Kids | KidzSearch.com the α-keratins in the hair (including wool ), horns , nails , claws and hooves of mammals the harder β-keratins in the scales and claws of reptiles , their shells ( chelonians , such as tortoise , turtle , terrapin ), and in the feathers , beaks , and claws of birds . (These keratins are formed primarily in beta sheets . However, beta sheets are also found in α-keratins.) [1] Arthropods such as crustaceans often have parts of their armor or exoskeleton made of keratin, sometimes in combination with chitin . Keratins are also found in the gastrointestinal tracts of many animals, including roundworms (who also have an outer layer made of keratin). 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.

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. 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. References ↑ 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 . Other websites

Question: What is the name for the protein which is the main constituent of hair, horns, nails, claws and hooves of mammals?
Answer: Keratin