Sheets fitted, folding

Fold a sheet of paper lengthwise. Curl the folded paper so that it fits inside the 600 mL beaker. Invert the beaker on your lab bench. 

Not all of the fibroin protein is in / -sheets. As the amino acid composition in Figure 6.12 shows, fibroin contains small amounts of other, bulky amino acids like valine and tyrosine, which would not fit into the structure shown. These are carried in compact folded regions that periodically interrupt the sheet segments, and they probably account for the amount of stretchiness that silk fibers have. In fact, different species of silkworms produce fibroins with different extents of such non - / -sheet structure and corresponding differences in elasticity. The overall fibroin structure is a beautiful example of a protein molecule that has evolved to perform a particular function — to provide a tough, yet flexible fiber for the silkworm s cocoon or the spider s web. 

While not a completed model of a single-strand sheet, Tew s extended sheet-like structures [75,76] lack only connections between individual strands to fit the definition. In this case, structures were assembled at an air-water interface, and controlled by amphiphilic patterning as well as TT-stacking. X-ray studies confirmed an organized sheet-like structure in aqueous solution indicating that the patterning of polar and non-polar functionality is a path to sheet formation [76b]. These strand-Uke stractures were shown to have biological activity similar to many sheet folded peptides [26]. 

The influence of the protein component of cytochrome c on the haem has also been investigated with the new technique of Raman difference spectroscopy. The basis of the method is similar to conventional difference spectroscopy and the resolution of the haem resonance has been increased S-fold. The method has also been used to study structural changes in methaemoglobin. Williams et a/. have used numerical methods to produce and interpret Raman difference spectra. These workers subtracted solvent spectra from protein spectra and showed that the amide I Raman scattering intensity could be used to define helix, sheet, and reverse turns with unparalleled accuracy. The method depends on computing reference spectra for each variety of secondary structure and fitting these in linear combination to the observed spectrum. The same technique has also been successfully applied to the amide III spectrum of proteins in deuterium oxide. ... 

The proposal that transverse sectioning of natural cellulose fibres can be used to test theories on the structure of microfibrils has been examined theoretically. It was concluded that fibre-sectioning experiments described in the literature do not disprove the folded-chain model, and it was suggested that clearly divided sections exist along the axis of the microfibril at intervals of 200 A. This cannot be explained in terms of a fringed micelle model. However, it is possible that cellulose II has a folded-chain conformation, since a single molecule of cellulose can be folded back and forth in the (101) plane to form a sheet-like structure that fits into the unit cell. A cellulose molecule can achieve a sharp U-tum in the... 

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