In a protein structure diagram, how can you distinguish an alpha helix depicted as a ribbon from one depicted as a cylinder?

• A. A ribbon depiction shows a flat, twisted shape, while a cylinder depiction shows a solid, tubular shape.
• B. A ribbon depiction shows a solid, tubular shape, while a cylinder depiction shows a flat, twisted shape.
• C. A ribbon depiction is always colored, while a cylinder depiction is always gray.
• D. Both depictions are identical and cannot be distinguished.

Answer: (A)