Page 8 of 11

Helix Flexibility

Both the model and real DNA helices can be deformed from their linear shape into curves and bends. Real DNA does this as a result of normal thermal motion and under the influence of certain proteins which bind to DNA. The nucleosome which is a DNA packing structure is one example where DNA is held in a non-linear form. Each nucleosome consists of a core of   histone proteins around which the DNA double helix is wrapped some 1.6 turns. Other proteins such as DNA transcription factors also alter the geometry of DNA and thereby modify its ability to be transcriped into RNA. Above is a model of DNA deformed into a circle. This requires just over 8 helical turns (50 base pairs). If you build this model, be sure to attach the same strand to itself when closing the circle.