In the spiral line, there is no crystalline β-sheet region.Įach spider and each type of silk has a set of mechanical properties optimised for their biological function. In the structural modules diagram, a microscopic structure of dragline and radial lines is shown, composed mainly of two proteins of MaSp1 and MaSp2, as shown in the upper central part. The large amount of β-spiral structure gives elastic properties to the capture part of the orb web. In the dragline and radial line, a crystalline β-sheet and an amorphous helical structure are interwoven. Microscopically, the spider silk secondary structure is formed of spidroin and is said to have the structure shown on the right side. Attachment cement secreted from the piriform gland is used to connect and fix different lines. Sticky balls drawn in blue are made at equal intervals on the spiral line with viscous material secreted from the aggregate gland. The red lines represent the dragline, radial line, and frame lines, the blue lines represent the spiral line, and the centre of the orb web is called the "hub". On the left is shown a schematic drawing of an orb web. Schematic of the spider's orb web, structural modules, and spider silk structure. The results show that ordered regions (i) mainly reorient by deformation for low-stretched fibres and (ii) the fraction of ordered regions increases progressively for higher stretching of the fibres. It has been possible to relate microstructural information and macroscopic mechanical properties of the fibres. Sizes of the nanofibrillar structure and the crystalline and semi-crystalline regions were revealed by neutron scattering. This model has refined over the years: semi-crystalline regions were found as well as a fibrillar skin core model suggested for spider silk, later visualised by AFM and TEM. This first very basic model of silk was introduced by Termonia in 1994 who suggested crystallites embedded in an amorphous matrix interlinked with hydrogen bonds. Potassium nitrate is believed to prevent the protein from denaturing in the acidic milieu. Potassium hydrogen phosphate releases hydrogen ions in aqueous solution, resulting in a pH of about 4, making the silk acidic and thus protecting it from fungi and bacteria that would otherwise digest the protein. It occurs in especially high concentration in glue threads. Pyrrolidine has hygroscopic properties which keeps the silk moist while also warding off ant invasion. Various compounds other than protein are used to enhance the fibre's properties. It is the interplay between the hard crystalline segments, and the strained elastic semi-amorphous regions, that gives spider silk its extraordinary properties. On a secondary structure level, the short side chained alanine is mainly found in the crystalline domains ( beta sheets) of the nanofibril, glycine is mostly found in the so-called amorphous matrix consisting of helical and beta turn structures. The primary structure is the amino acid sequence of its proteins ( spidroin), mainly consisting of highly repetitive glycine and alanine blocks, which is why silks are often referred to as a block co-polymer. Silks, like many other biomaterials, have a hierarchical structure. The crystals are beta-sheets that have assembled together. Inside a typical fibre there are crystalline regions separated by amorphous linkages. Properties Structural Structure of spider silk. However, the function of male-produced silk in mating has received very little study. Observations of male spiders producing silk during sexual interactions are also common across phylogenetically widespread taxa. Silk produced by females provides a transmission channel for male vibratory courtship signals, while webs and draglines provide a substrate for female sex pheromones. While methods have been developed to collect silk from a spider by force, it is difficult to gather silk from many spiders compared to silk-spinning organisms such as silkworms.Īll spiders produce silk, and even in non-web-building spiders, silk is intimately tied to courtship and mating. In some cases, spiders may even use silk as a source of food. Most spiders vary the thickness and adhesiveness of their silk for different uses. They can also use the silk to suspend themselves from height, to float through the air, or to glide away from predators. Spiders use silk to make webs or other structures that function as adhesive traps to catch prey, to entangle and restrain prey before biting, to transmit tactile information, or as nests or cocoons to protect their offspring. Spider silk is a protein fibre or silk spun by spiders. Indian Summer by Józef Chełmoński (1875, National Museum in Warsaw) depicts a peasant woman with a thread of gossamer in her hand. For the genus of bryozoans, see Arachnidium (bryozoan).Ī female specimen of Argiope bruennichi wraps her prey in silk.
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