Sequential polypeptides result in new polypeptide conformations with diverse biological roles. Collagen, a polytripeptide, is a familiar and unique structural protein: gramicidin A, an L-D polydipeptide, forms cation selective channels in biomembranes; a synthetic polytripeptide forms cation-selective voltage-dependent channels in lipid bilayers; the polypentapeptide of tropoelastin is a biological elastomer; and the pohtelra- and polyhexapeptides of tropoelastin can be ascribed specific functional roles. From these few examples one recognizes the almost limitless potential of studies on polysequential peptides. In the description of new helical conformations derived from repeating peptide sequences, the concept of cyclic conformations with linear conformational correlates is useful particularly in derivation, or even design, of single-stranded helical structures with a large number of residues per turn. The repeating peptide becomes a repeating conformational unit that can repeat on a helix axis. A common repeating conformational feature is the β turn, and helical repetitions of conformational units in which the β turn is the dominant conformational feature are designated β spirals.