The Structure of Life


Metal working model used by James Watson and Francis Crick to determine the double-helical structure of the DNA molecule in 1953

 
 

In molecular biology, the term double helix refers to the structure formed by double-stranded molecules of nucleic acids such as DNA. The double helical structure of a nucleic acid complex arises as a consequence of its secondary structure, and is a fundamental component in determining its tertiary structure. The term entered popular culture with the publication in 1968 of The Double Helix: A Personal Account of the Discovery of the Structure of DNA, by James Watson.

In 1953, James Watson and Francis Crick suggested what is now accepted as the first correct double-helix model of DNA structure in the journal Nature. Their double-helix, molecular model of DNA was then based on a single X-ray diffraction image (labeled as “Photo 51”) taken by Rosalind Franklin and Raymond Gosling in May 1952, as well as the information that the DNA bases are paired—also obtained through private communications from Erwin Chargaff in the previous years. Chargaff’s rules played a very important role in establishing double-helix configurations for B-DNA as well as A-DNA.

 
 

A segment of the very long DNA molecule—the double helix. Physically, DNA resembles a spiral staircase. Each rung of the ladder is composed of two chemicals, called nucleotides or base pairs, that are chemically bonded to each other. DNA has four nucleotides: adenine, thymine, guanine, and cytosine, usually abbreviated by the first letter of their names- A, T, G, and C.

 
 

A caduceus—the staff carried by Hermes, “the messenger of the gods.” Is its double-helical structure an ancient Greek premonition of the most vital ‘message of the gods,’ or simply a coincidence. It is said the wand would wake the sleeping and send the awake to sleep. If applied to the dying, their death was gentle; if applied to the dead, they returned to life.

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