Domain walls on graphite mimic DNA.

We show that domain walls on graphite are very likely to mimic features of extended macromolecules like DNA strands, when imaged with an STM. We explain with a simple model how different translational periods along a grain boundary originate from different relative orientations of the graphite lattice at the domain wall. We show how simple geometrical analysis of the images can be used to distinguish true macromolecular features from artifacts.