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Chapter 9 : Sizes of the Escherichia coli and Human Genomes
DNA is stored in cells in the form of chromosomes and plasmids. One of the wonders of biology is that cells are able to store and access the great lengths of DNA needed to encode their hereditary information. The "average" protein-encoding bacterial gene is considered to be 1,200 bp in length. It is capable of high degrees of folding and coiling, an essential feature for packing it into the cell. The Escherichia coli chromosome is circular and is attached to the cell membrane. The real E. coli chromosome occupies about 10% of the cell volume. The human genome can be related to a length of railroad track. The railroad ties represent the base pairs, and the rails represent the sugar-phosphate backbone of the DNA molecule.