text: One structure with this shape exhibits a double peak at 208 and 222 nm in circular dichroism spectroscopy.
full_question: One structure with this shape exhibits a double peak at 208 and 222 nm in circular dichroism spectroscopy. Certain structures with this shape are formed via Hoogsteen interactions. A molecule with this structure typically exists in a B form and contains a major and minor groove. A protein which takes this shape has glycine at roughly every three residues, and contains high amounts of proline and hydroxyproline. Collagen's three strands form this shape. This structure was elucidated by the X-ray crystallography of Maurice Wilkins and Rosalind Franklin. For 10 points, name this shape, a "double" variety of which forms DNA.
first_sentence: One structure with this shape exhibits a double peak at 208 and 222 nm in circular dichroism spectroscopy.
raw_answer: helix [or double helix; or triple helix; or quadruple helix]