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DNA. X-ray diffraction image of part of a molecule of DNA (Deoxyribonucleic Acid). DNA is the carrier molecule of the genetic code. A repeated pattern is seen here which reveals the helical (spiral) structure of DNA around a core. X-ray diffraction (or X-ray crystallography) is a way of determining the structure of molecules by bombarding a crystal sample with X-rays. An image such as this played the major role in the unraveling of the double helix structure of the DNA molecule by James Watson and Francis Crick in 1953. (KEYSTONE/SCIENCE PHOTO/Science Source) === ===