Structural mechanics of bent DNA.

The DNA molecule is a familiar object. It is often depicted in magazines and advertisements as a double helix, with the letters of the genetic code strung along the two spiral backbones and joined together in pairs. In such pictures the molecule is usually shown as straight; yet in the chromosomes of living organisms, DNA is curved and wound up into condensed packages. This article explains what is involved in such bending of DNA in the cell. It uses the ideas of structural mechanics--a tool of engineers--to show how the various components fit together when the molecule is bent.