A-Helix form

In 1951, American chemists Linus Pauling and Robert Corey suggested that proteins could exist in the shape of an a-helix, a form in which a single protein chain twists so that it resembles a coiled helical spring (see P Figure 9.6). The chain is held in the helical shape... 

Both DNA and RNA are polymers their monomer units are called nucleotides and consist of three parts a phosphate group, a pentose (5-carbon sugar) and a nitrogen-containing base. The DNA molecules vary in size, but they can have as many as 30,000 base pairs, and they are the largest of all natural molecules. We now know that the three-dimensional staicture of DNA is a double helix a form resembling a spiral staircase. The outside handrails are the sugar-phosphate... 

Figure 2, WAXD and SAXS patterns of P(3HB-co 8%-3HV) cold-drawn and annealed films (A and B) 10 times drawn film, and (C and D) 16 times drawn film, (E) Two kinds of molecular conformations (21 helix (a-form) and planar zi ag form) conformations) of P(3HB) built by using the atomic coordinates reported, in ref. 16 and ref 18, respectively. Arrow indicates a reflection derivedfrom form.

Both stretched films and fibers had two kinds of molecular conformations, 21 helix (a-form) and planar zigzag (/9-form) conformations. The improvement of mechanical properties is due to the generation of -form that exists between a-form lamellar crystals. In SAXS patterns of highly stretched films and fibers, the intensities of reflections along the stretching direction, which indicate the long period of lamellar crystals, remarkably decreased, suggesting that two crystalline forms have almost same crystal densities. 

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See also in sourсe #XX -- [ ]

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