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Wrapped up prey Gluey aggregate beads up on flagelliform fibers. Spigot Protein motifsSpider silks contain proteins made up of blocks of recurring alanine and glycine amino acids. Alanineblocks typically pack together in dense, tiny crystals. These areseparated by glycine blocks that make up amorphous regions.The combination makes the silkstrong and flexible. This spider has six spinnerets (two shown, right), each with many silk spigots. Spidroidproteinssecreted Liquid silkstored, acidicglycoproteincoat added Excess water removed Major ampullateFrame, dragline, radii, hub Glands: PiriformCementlike bonding TubuliformOuter layer of egg case Minor ampullateTemplate spiral FlagelliformPermanent spiral lines AggregateGlue for prey capture and web structure A SPINNER’S SECRETSAll spiders spin silk, with glands that produce custom blends of proteins with different “motifs” that impart just the right properties for each use. The silks exit the abdomen through spinnerets. Spinneret LegoThese regions contain repeating alanines that lock together, adding toughness. SlinkyThese motifs are rich inthe amino acids glycineand proline and help givesilks their stretchiness. ZipperOther glycine-rich regions zip together, forming helixes that confer flexibility. A living textile factory The golden orb-weaver has seven kinds of silk glands (distinguished left, by color), with each generating a specific liquid of silk proteins, or spidroids, that are chemically modified, solidified into a fiber, and extruded from a spigot. (Only one of the many glands of each type is shown.) Silk’s many uses Colors denote the type of silk used in the different parts of the web, as well as for wrapping and pinning down prey and for making egg cases. One protein Graphic by Valerie Altounian;Text by Elizabeth PennisiandRobert F. Service Egg sacs AciniformPrey wrapping and egg case insulation

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