β-sheets are extended structures; what directional characteristic do parallel β-sheets have?

Parallel β-sheets have strands that run in the same direction, which means that the amino acid sequences of the strands are oriented identically from N-terminus to C-terminus. This orientation leads to specific hydrogen bonding patterns, as the carbonyl oxygen of one amino acid on one strand forms a hydrogen bond with the amide hydrogen of an amino acid on the adjacent strand. This alignment is crucial for the stability and structural integrity of the β-sheet.

In contrast, antiparallel β-sheets feature strands that run in opposite directions, leading to a different hydrogen bonding arrangement. Random orientation or periodic switching of directions does not represent the typical structure of parallel β-sheets, which necessitate the strands to be uniformly aligned for optimal hydrogen bonding. Understanding this directional characteristic is essential for grasping protein secondary structures and their implications in biochemical functions.