ABSTRACT
In the age of genomics, the biology of the cell is dominated by a DNA-centered view. The DNA molecule is a nucleic acid built from two single strands of nucleotides. DNA is wrapped around the nucleosome in a left-handed manner, opposite to the winding of the DNA helix. Specific divalent ions, however, and in particular ions of higher valency, have important structural effects on the DNA molecule itself. When comparing the bands of the broken DNA strands in gel electrophoresis, a gap will appear in the resulting gel ladder at the position of the protected sequence. The B-DNA structure is the biologically most relevant one, and also the one originally observed in X-ray crystallography. X-rays and transmission electron microscopy (TEM) are two methods for the imaging of molecular or material structures since both energetic photons and electrons can be diffracted at the molecular structure.
