| Chapter 5: An Introduction to CarbohydratesCarbohydrate- (sugar) that encompasses the monomers calledmonosaccharides,oligosaccharides, andpolysaccharides(CH2O)m.Monosaccharides- monomers with “one sugar”Oligosaccharides- small polymers with “few sugars”Polysaccharides- large polymers with “many sugars”Made up of carbonyl group (C-O), several hydroxyl groups (-OH), along w/multiplecarbon-hydrogen bonds (C-H).Formaldehyde is NOT a carbohydrate because it does not have a hydroxyl group.5.1: Sugars as MonomersSugars provide chemical energy in cellsWhat Distinguishes One Monosaccharide from Another?-Monosaccharides are monomers of carbohydrates-Difference between two monosaccharides is:1.structure-carbonyl groups (C-O) are in different places-Form different sugars (e.g. aldose, ketone)-Have multiple polar hydroxyl groups (-OH), even the simplest sugars havereactive and hydrophilic functional groups-why they dissolve in aqueoussolutions so easily2.number of carbon atoms presenttrioses- three-carbon sugarspentose- five carbon-sugars;in ribose, which acts as a building block for nucleotideshexose- six-carbon sugar (glucose)3.spatial arrangement of their atoms-think as direction (up or down) as the difference; (4thcarbon)
Updated November 22, 2019 By J. Dianne Dotson
Arthropods (insects and crustaceans) are known for their hard outside covering, or exoskeleton. The exoskeleton allows for joint movement while it covers up soft tissues inside an arthropod’s body.
The main structural material in some external skeletons is a complex carbohydrate called chitin.
Chitin is an organic compound that was discovered by Henri Braconnot, a chemist, in 1811. It gets its name from the Greek word chiton, which was the word for "mail" (as in "armor"). It is present in exoskeleton animals such as insects and crustaceans, but also in fungi cell walls. Chitin provides a frame structure for these animals to protect their internal organs and muscles.
Chitin is a complex carbohydrate, the most prevalent aminopolysaccharide polymer in nature. It is second only to cellulose as the most abundant polysaccharide on Earth. Its structure is quite similar to cellulose, but it has different glucose monomer units.
The chemical name for chitin is poly (β-(1-4)-N-acetyl-D-glucosamine. Chitin can be converted to the derivative called chitosan using enzymes or deacetylation. Chitosan is more water-soluble than chitin, and it is often used in bandages, seed coatings and in winemaking.
Chitin is a transparent, flexible material, and in some organisms such as crustaceans, it can be combined with calcium carbonate to make it even stronger. Chitin can be degraded in nature by bacteria.
Chitin provides the main structural material in some external skeletons. This framework is rigid and covers the soft tissues underneath. It also provides muscles with a material to pull.
The protective shell of chitin gives exoskeleton animals an advantage because it works as a kind of armor. Exoskeletons are made of joints that allow better leverage for animals to move their limbs.
This better leverage makes the animals stronger relative to their size than animals without an outer frame architecture of chitin. Chitin can also be found in the mandibles of some organisms, such as snails.
With increasing size, a chitin exoskeleton would become impractical for an animal, making it too heavy to move around. This is why arthropods tend to be tiny in comparison to large vertebrates.
Another distinct disadvantage happens when exoskeleton animals shed or molt their chitin shell as they grow. There can be as many as six molts between the hatching of an insect and when it becomes an adult.
When this occurs, breathing is impeded because the animal's tracheole lining comes out along with its exoskeleton. This puts insects at risk, and the situation worsens with increased temperatures.
In addition to being the main structural material in some external skeletons, chitin has proven to be useful in numerous manmade materials. Nanotechnology has used chitin and chitosan to make polymer scaffolds.
Chitin and chitin-based compounds have also been used for biomedical applications. The frame structure that chitin and chitosan provide make it invaluable for making composite scaffolds for wound healing and blood-clotting. This is due to the crystalline microfibrils within chitin that make it so stable for exoskeletons and the cell walls of fungi.
Chitin-based compounds are also used for drug delivery, biological recognition ligands for cancer diagnosis, ophthalmology, vaccine adjuvants and fighting tumors.
Chitin and chitosan are nontoxic, biocompatible, microbial and biodegradable. They have great structural integrity, are highly porous and can degrade at a predictable rate. Solvents can extract chitin from crustacean shells for use in other materials.
The second most abundant carbohydrate on Earth provides structure and function to organisms in the natural world, as well as modern technology.
Future advancements based on the stability and flexibility of chitin should provide agriculture, biotechnology, nanomedicine and other fields with a powerful component to aid humanity. Chitin (C8H13O5N)n (/ˈkaɪtɪn/ KY-tin) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. The second most abundant polysaccharide in nature[1] (behind only cellulose), it is a primary component of cell walls in fungi, the exoskeletons of arthropods such as crustaceans and insects, and the radulae, cephalopod beaks and gladii of molluscs.
It is also synthesised by at least some fish and lissamphibians.[2] The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. Chitin has proved useful for several medicinal, industrial and biotechnological purposes.
The English word "chitin" comes from the French word chitine, which was derived in 1821 from the Greek word χιτών (khitōn) meaning covering.[3] A similar word, "chiton", refers to a marine animal with a protective shell. Chemical configurations of the different monosaccharides (glucose and N-acetylglucosamine) and polysaccharides (chitin and cellulose) presented in Haworth projection The structure of chitin was determined by Albert Hofmann in 1929. Hofmann hydrolyzed chitin using a crude preparation of the enzyme chitinase, which he obtained from the snail Helix pomatia.[4][5][6] Chitin is a modified polysaccharide that contains nitrogen; it is synthesized from units of N-acetyl-D-glucosamine (to be precise, 2-(acetylamino)-2-deoxy-D-glucose). These units form covalent β-(1→4)-linkages (like the linkages between glucose units forming cellulose). Therefore, chitin may be described as cellulose with one hydroxyl group on each monomer replaced with an acetyl amine group. This allows for increased hydrogen bonding between adjacent polymers, giving the chitin-polymer matrix increased strength. A cicada emerges from its chitinous larval exoskeleton. In its pure, unmodified form, chitin is translucent, pliable, resilient, and quite tough. In most arthropods, however, it is often modified, occurring largely as a component of composite materials, such as in sclerotin, a tanned proteinaceous matrix, which forms much of the exoskeleton of insects. Combined with calcium carbonate, as in the shells of crustaceans and molluscs, chitin produces a much stronger composite. This composite material is much harder and stiffer than pure chitin, and is tougher and less brittle than pure calcium carbonate.[7] Another difference between pure and composite forms can be seen by comparing the flexible body wall of a caterpillar (mainly chitin) to the stiff, light elytron of a beetle (containing a large proportion of sclerotin).[8] In butterfly wing scales, chitin is organized into stacks of gyroids constructed of chitin photonic crystals that produce various iridescent colors serving phenotypic signaling and communication for mating and foraging.[9] The elaborate chitin gyroid construction in butterfly wings creates a model of optical devices having potential for innovations in biomimicry.[9] Scarab beetles in the genus Cyphochilus also utilize chitin to form extremely thin scales (five to fifteen micrometres thick) that diffusely reflect white light. These scales are networks of randomly ordered filaments of chitin with diameters on the scale of hundreds of nanometres, which serve to scatter light. The multiple scattering of light is thought to play a role in the unusual whiteness of the scales.[10][11] In addition, some social wasps, such as Protopolybia chartergoides, orally secrete material containing predominantly chitin to reinforce the outer nest envelopes, composed of paper.[12] Chitosan is produced commercially by deacetylation of chitin; chitosan is soluble in water, while chitin is not.[13] Nanofibrils have been made using chitin and chitosan.[14] Chitin-producing organisms like protozoa, fungi, arthropods, and nematodes are often pathogens in other species.[15] Humans and other mammalsHumans and other mammals have chitinase and chitinase-like proteins that can degrade chitin; they also possess several immune receptors that can recognize chitin and its degradation products in a pathogen-associated molecular pattern, initiating an immune response.[15] Chitin is sensed mostly in the lungs or gastrointestinal tract where it can activate the innate immune system through eosinophils or macrophages, as well as an adaptive immune response through T helper cells.[15] Keratinocytes in skin can also react to chitin or chitin fragments.[15] According to in vitro studies, chitin is sensed by receptors, such as FIBCD1, KLRB1, REG3G, Toll-like receptor 2, CLEC7A, and mannose receptors.[15][16] The immune response can sometimes clear the chitin and its associated organism, but sometimes the immune response is pathological and becomes an allergy;[17] allergy to house dust mites is thought to be driven by a response to chitin.[16] PlantsPlants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1 and chitin elicitor-binding protein.[15] The first chitin receptor was cloned in 2006.[18] When the receptors are activated by chitin, genes related to plant defense are expressed, and jasmonate hormones are activated, which in turn activate systematic defenses.[19] Commensal fungi have ways to interact with the host immune response that, as of 2016[update], were not well understood.[18] Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors.[19][20] Zymoseptoria tritici is an example of a fungal pathogen that has such blocking proteins; it is a major pest in wheat crops.[21] Chitin was probably present in the exoskeletons of Cambrian arthropods such as trilobites. The oldest preserved chitin dates to the Oligocene, about 25 million years ago, consisting of a scorpion encased in amber.[22] Chitin is a good inducer of plant defense mechanisms for controlling diseases.[23] It has potential for use as a soil fertilizer or conditioner to improve fertility and plant resilience that may enhance crop yields.[24][25] IndustrialChitin is used in industry in many processes. Examples of the potential uses of chemically modified chitin in food processing include the formation of edible films and as an additive to thicken and stabilize foods and food emulsions.[26][27] Processes to size and strengthen paper employ chitin and chitosan.[28][29] How chitin interacts with the immune system of plants and animals has been an active area of research, including the identity of key receptors with which chitin interacts, whether the size of chitin particles is relevant to the kind of immune response triggered, and mechanisms by which immune systems respond.[17][21] Chitin and chitosan have been explored as a vaccine adjuvant due to its ability to stimulate an immune response.[15] Chitin and chitosan are under development as scaffolds in studies of how tissue grows and how wounds heal, and in efforts to invent better bandages, surgical thread, and materials for allotransplantation.[13][30] Sutures made of chitin have been explored for many years, but as of 2015[update], none were on the market; their lack of elasticity and problems making thread have prevented commercial development.[31] In 2014, a method for using chitosan as a reproducible form of biodegradable plastic was introduced.[32] Chitin nanofibers are extracted from crustacean waste and mushrooms for possible development of products in tissue engineering, medicine, and industry.[33] In 2020, chitin was proposed for use in building structures, tools, and other solid objects from a composite material of chitin combined with Martian regolith.[34] In this scenario, the biopolymers in the chitin act as the binder for the regolith aggregate to form a concrete-like composite material. The authors believe that waste materials from food production (e.g. scales from fish, exoskeletons from crustaceans and insects, etc.) could be put to use as feedstock for manufacturing processes.
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What holds chitin molecules together to be able to form a stiff protective armor in some animals?
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