5.03: The Double Helix of DNA

Diagram of the DNA double helix drawn as two thick black ribbons twisting around each other. The strands run antiparallel: at the top, the left strand is labeled 5' and the right strand 3'; at the bottom, the left strand is 3' and the right strand 5'. Horizontal black bars between the ribbons represent paired bases. Red labels with arrows identify the components: 'Phosphates' points to circles in the backbone near the upper left; 'Bases' points to the horizontal bars in the middle; 'Deoxyribose' points to pentagon-shaped sugars in the backbone near the lower left. In two uncoiled regions (upper right and lower left), the backbone chemistry is drawn out, showing alternating circles (phosphates) and pentagons (deoxyribose) connected in chains, each sugar attached to a base bar, with 5' and 3' positions marked on the sugars. Vertical dimension arrows on the right indicate 3.4 ?? between adjacent base pairs and 34 ?? for one complete helical turn (about ten base pairs per turn).

This structure of DNA was worked out by Francis Crick and James D. Watson in 1953. It revealed how DNA - the molecule that Avery had shown was the physical substance of the genes. It could be replicated and so passed on from generation to generation. For this epochal work, they shared a Nobel Prize in 1962.