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Chapter 9 : Modeling Genome Size
The activity described in this chapter uses models to show the relative sizes of an Escherichia coli cell, the E. coli chromosome, a typical plasmid, and a gene. The models demonstrate graphically how much longer the E. coli chromosome is than the cell. Calculations included in the student questions use the analogies of letters in a book and miles of railroad track to suggest the size of the human genome. DNA is stored in cells in the form of chromosomes and plasmids. The amount of DNA required to store the information necessary for making even a simple organism, such as a bacterial cell, is very large. 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. It is capable of high degrees of folding and coiling, an essential feature for packing it into the cell. Although the degree of folding required to fit the DNA of E. coli into the bacterium is impressive, the folding necessary for packaging DNA into a human cell is even more remarkable. The DNA models consist of appropriate lengths of thread, yarn, or string. At the end of the activity students will able to list some differences between the E. coli and human genomes.