How was X-ray diffraction used to help discover the shape of DNA?

How was X-ray diffraction used to help discover the shape of DNA?

• A. It directly imaged the double helix
• B. It produced diffraction patterns that suggested a helical structure
• C. It measured the DNA base composition
• D. It produced diffraction patterns that indicated a helical structure

Answer: (D)

X-ray diffraction works by sending X-rays through highly ordered material and analyzing the resulting pattern of scattered waves. For DNA, the diffraction pattern from the fibers showed a distinctive X-shaped cross, which is a hallmark of a helix. The way the spots are arranged—their angles and spacing—encodes a regular, helical geometry, revealing a specific diameter and a repeating unit along the axis. This pattern provided strong evidence that DNA has a helical structure, which helped scientists settle on the idea of a helix and later the double-helix model. It’s important to note that this method doesn’t produce a direct image of the molecule, nor does it tell you what bases are present; it gives information about the overall shape and arrangement through the diffraction pattern.

X-ray diffraction works by sending X-rays through highly ordered material and analyzing the resulting pattern of scattered waves. For DNA, the diffraction pattern from the fibers showed a distinctive X-shaped cross, which is a hallmark of a helix. The way the spots are arranged—their angles and spacing—encodes a regular, helical geometry, revealing a specific diameter and a repeating unit along the axis. This pattern provided strong evidence that DNA has a helical structure, which helped scientists settle on the idea of a helix and later the double-helix model. It’s important to note that this method doesn’t produce a direct image of the molecule, nor does it tell you what bases are present; it gives information about the overall shape and arrangement through the diffraction pattern.