Sheet conformation

The VMS sulphides define a broadly conformable sheet 5-50 m below the base of the BLUC. This synformal surface of mineralisation generally coincides with the transition from ultramafic cumulates and strongly foliated metavolcanic rocks to an underlying sequence of metavolcanic rocks and interflow metawacke and metasiltstone rocks (Fig. 2). Sphalerite-pyrrhotite mineralisation in hydrothermal veins was also observed within the BLUC several km west of this study area. 

There are two fundamental conformations that are essentially strain-free, namely ( ) = 120° and / = 120° (Figs. 9.2.4 and 9.2.5 only linear conformation, sheet) and = -60° (a-helix) (Fig. 9.2.6). They have minimal Pitzer and Newman strains, and the linear conformer is even free of allylic strain. Furthermore, interchain (intercatenar) NHCO-hydrogen bonding is optimal in the ( ) = -120° and / = -60° conformation. The allylic strain present in the latter conformer is overcome by this favorable dipole interaction in the right-handed helix (Fig. 9.2.6) (Ramachandran and Sasisekharan, 1968). 

Since the early 1980s, techniques for producing relatively coarse but very useful fibers or fiber-like tapes from films have been developed. Obviously, the first step in this operation is the production of a film. Films are manufactured in two conformations—sheet and blown films. Because the blown film operation is more complicated and because it produces a less fibrillatable film due to a more ordered crystalline structure and lateral orientation, it is not widely used and will not be discussed further. 

The primary structure of a peptide is its ammo acid sequence We also speak of the secondary structure of a peptide that is the conformational relationship of nearest neighbor ammo acids with respect to each other On the basis of X ray crystallographic studies and careful examination of molecular models Linus Pauling and Robert B Corey of the California Institute of Technology showed that certain peptide conformations were more stable than others Two arrangements the a helix and the (5 sheet, stand out as... 

Secondary structure (Section 27 19) The conformation with respect to nearest neighbor ammo acids m a peptide or pro tern The a helix and the pleated 3 sheet are examples of protein secondary structures... 

PCTFE plastic is available in products that conform to ASTM 1430-89 Type 1 (Grades 1 and 2) and is suitable for processing into parts that meet MIL-P 46036 (Federal Specification LP-385C was canceled 1988). Standards for fabricated forms are available for compression molded heavy sections (AMS-3645 Class C), thin-walled tubing, rod, sheet, and molded shapes (AMS-3650). PCTFE plastics have been approved for use in contact with food by the FDA (55). 

Fig. 2. Protein secondary stmcture (a) the right-handed a-helix, stabilized by intrasegmental hydrogen-bonding between the backbone CO of residue i and the NH of residue t + 4 along the polypeptide chain. Each turn of the helix requires 3.6 residues. Translation along the hehcal axis is 0.15 nm per residue, or 0.54 nm per turn and (b) the -pleated sheet where the polypeptide is in an extended conformation and backbone hydrogen-bonding occurs between residues on adjacent strands. Here, the backbone CO and NH atoms are in the plane of the page and the amino acid side chains extend from C ...

Figure 2.5 Schematic illustrations of antiparallel (3 sheets. Beta sheets are the second major element of secondary structure in proteins. The (3 strands are either all antiparallel as in this figure or all parallel or mixed as illustrated in following figures, (a) The extended conformation of a (3 strand. Side chains are shown as purple circles. The orientation of the (3 strand is at right angles to those of (b) and (c). A p strand is schematically illustrated as an arrow, from N to C terminus, (bj Schematic illustration of the hydrogen bond pattern in an antiparallel p sheet. Main-chain NH and O atoms within a p sheet are hydrogen bonded to each other.

Chothia, C. Conformation of twisted p-pleated sheets in proteins. /. Mol. Biol. 75 295-302, 1973. 

Figure 13.10 Rearrangements of the hydrogen bond network between strands 1, 2, and 3 in the p sheet of Go. as a consequence of the switch from the GDP (blue) to the GTP (green) conformation. Strand P3 pulls away from pi and disrupts two hydrogen bonds in order to bring Gly 199 into contact with the y-phosphate of GTP. As a consequence new hydrogen bonds are formed between P2 and P3. (Adapted from D. Lambright et al.. Nature 369 621-628,...

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