(1992) David Viskochil collects super coiled DNA from cesium chloride gradients (separates plasmid DNA from bacterial chromosomal DNA). . DNA consists of two sugar- phosphate backbones, arranged in a double helix, linked by nucleotide bases. There are 4 types of base; adenine (A), cytosine (C), guanine (G) and thymine (T). Sequences of these bases make up genes, which encode an organism's genetic information. Howard Hughes Medical Institute, University of Utah, Salt Lake City, Utah. DNA Fingerprinting..