<prompt> Clusters of twisted strands of β sheet are calledAmphiphatic helicesβ barrelsLoops and bendsSupersecondary structures  <response>: Most β sheets are not perfectly flat but tend to have a right-handed twist. Clusters of twisted strands of β sheet, sometimes referred to as β barrels, form the core of many globular proteins.Ref: Harpers illustrated biochemistry. 30th edition page no: 39 