When Astbury steamed and stretched the wool and held it, the X-ray pattern showed a new repeating structural unit that was approximately 7.0 A long. When the stretched wool was allowed to shrink, the X-ray pattern again showed a repeating unit of approximately 5.2 A. What can you conclude about the structure of alpha-keratin in the steamed and stretched wool? When wool is steamed and stretched, the alpha-keratin backbone takes on a fully extended conformation and does not have any regular secondary structure elements. When wool is steamed and stretched, the disulfide bonds in alpha-keratin break. The polypeptide changes from the alpha conformation to the beta conformation, where the length of the repeated structural units is 7.0 A. When wool is steamed and stretched, the coiled-coil structure of alpha-keratin disrupts. The two strands of alpha-keratin become single alpha helices with repeating units that are approximately 7.0 A long. When wool is steamed and stretched, the alpha-keratin polypeptide extends and changes from the alpha conformation to the beta conformation, where the length of the repeated structural units is 7.0 A. Incorrect. Although it is true that steaming and stretching wool disrupts the coiled-coil structure of alpha-keratin, this process also disrupts the hydrogen bonds maintaining the stability of the individual alpha helices. Additionally, the length of each complete turn of an alpha helix is 5.4 A.