Dragline

Secondary Structure. The silkworm cocoon and spider dragline silks are characterized as an antiparaHel P-pleated sheet wherein the polymer chain axis is parallel to the fiber axis. Other silks are known to form a-hehcal (bees, wasps, ants) or cross- P-sheet (many insects) stmctures. The cross-P-sheets are characterized by a polymer chain axis perpendicular to the fiber axis and a higher serine content. Most silks assume a range of different secondary stmctures during processing from soluble protein in the glands to insoluble spun fibers. 

Crystallinity. Generally, spider dragline and silkworm cocoon silks are considered semicrystalline materials having amorphous flexible chains reinforced by strong stiff crystals (3). The orb web fibers are composite materials (qv) in the sense that they are composed of crystalline regions immersed in less crystalline regions, which have estimates of 30—50% crystallinity (3,16). Eadier studies by x-ray diffraction analysis indicated 62—65% crystallinity in cocoon silk fibroin from the silkworm, 50—63% in wild-type silkworm cocoons, and lesser amounts in spider silk (17). 

Thermal Properties. Spider dragline silk was thermally stable to about 230°C based on thermal gravimetric analysis (tga) (33). Two thermal transitions were observed by dynamic mechanical analysis (dma), one at —75° C, presumed to represent localized mobiUty in the noncrystalline regions of the silk fiber, and the other at 210°C, indicative of a partial melt or a glass transition. Data from thermal studies on B. mori silkworm cocoon silk indicate a glass-transition temperature, T, of 175°C and stability to around 250°C (37). The T for wild silkworm cocoon silks were slightly higher, from 160 to 210°C. 

Draglines are equipped with a 71-m bucket at the end of a 111-m boom and can be employed to dig both a portion of the overburden, which is free-cast into the mining pit, and the tar sand, which is piled in windrows behind the machine. Bucket-wheel reclaimers, similar to bucket-wheel excavators, load the tar sand from the windrows onto conveyor belts which transfer it to the plant. 

Simmons, A.H., Michal, C.A., Jelinski, L.W. Molecular orientation and two-component nature of the crystalline fraction of spider dragline silk. Science 271 84-87, 1996. 

Thiel, B.L., Kunkel, D.D., Viney, C. Physical and chemical microstructure of spider dragline a study by analytical transmission electron microscopy. Biopolymers 34 1089-1097, 1994. 

Xu, M., Lewis, R.V. Structure of a protein superfiber spider dragline silk. Proc. Natl. Acad. Sci. USA 87 7120-7124, 1990. 

Charlotte s Web Revisited Helix-Sheet Composites in Spider Dragline Silk... 

A dragline at Atlantic Richfield s Black Thunder strip mine in Gillette, Wyoming, loads coal into a dump truck. The coal is transported to cities around the country where it is burned to generate electricity. (Corbis-Bettmannj... 

Mechanical dredging. Mechanical dredging methods use mechanical excavation equipments such as backhoes, draglines, clamshells, and bucket ladder dredges. 

Figure 10 shows polarized spectra of two types of silks recorded by Raman spectromicroscopy the dragline silk (the lifeline) of the spider Nephila edulis and the cocoon silk of a wild silkworm Sarnia cynthia ricini. The position of the amide I band at 1,668-1,669 cm-1 for both threads is characteristic of the /i-sheet... 

Figure 10 Polarized spectra obtained by Raman microspectroscopy of (A) the dragline silk of the spider Nephila edulis and (B) the cocoon silk of the silkworm Sarnia cynthia ricini. Adapted with permission from Rousseau et al. [63]. Copyright 2004 American Chemical Society.

The dragline silk is composed of the two spidroins MaSpI and MaSpII. A 2.4-kb segment from the 3 end of the original MoSpl-mRNA and a 2-kb segment from the... 

MA Dragline radial threads MASp 1 and 2 ( ) (GA) /(A) / -structure GPGGX/GPGQQ /Lspiral GGX 3j helix =2-8 Gly (38), Ala (29), SSC (70), PC (21) Low concentration disorder/PPII High concentration helical/molten globule 0-Sheet 15-30 35... 

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