Principles of Biochemistry Volume 3 - A. Lehninger 1985

Molecular mechanisms of genetic information transfer
DNA: Structure of chromosomes and genes
Eukaryotic cells contain significantly more DNA than prokaryotes

Now we will make a major leap and move from Prokaryotic Cells to much more complex Eukaryotic cells. Eukaryotes contain significantly more DNA than prokaryotes. A single Cell of a slime mold, one of the most primitive eukaryotes, contains more than 10 times The amount of DNA found in an E. coli cell. In the Cells of the fruit fly

Drosophila, used in classical genetic research, the amount of DNA exceeds that in E. coli cells by more than 25 times. Meanwhile, human cells and those of many other mammals contain approximately 600 times more DNA than E. coli.

The total physical length of all DNA in a single human cell is ~2 m (for comparison, the length of E. coli DNA is 1.4 mm). Since an adult human body contains ~10¹³ cells, the total length of all human DNA is ~2∙10¹³ m, or 2∙10¹⁰ km. Compare this value with the Earth's circumference (4∙10⁴ km) or the distance from the Earth to the Sun (1.44∙10⁸ km)!

Microscopic observation of The Nucleus of dividing eukaryotic cells reveals that their genetic material is distributed among Chromosomes, the number of which varies depending on the species (Table 27-5). A human cell, for example, contains 46 chromosomes. It is now established that each chromosome in a Introduction/5.html">Eukaryotic Cell, such as the one shown in Fig. 27-21, contains a single very large double-stranded DNA molecule, the length of which can be 4 to 100 times greater than that of E. coli DNA. For instance, the physical length of the DNA molecule in one of the smallest Human chromosomes is ~30 mm, which is nearly 15 times the length of an E. coli DNA molecule. The DNA molecules in the forty-six human chromosomes vary in size, differing by more than 25-fold. Eukaryotic DNA is linear rather than circular. Each eukaryotic chromosome carries a unique set of genes. The entire Complement of a cell's genes constitutes its genome.

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Fig. 27-21. Electron micrograph of human chromosome 12.

Table 27-5. Normal chromosome number in various species

A typical human cell, such as a Liver cell, is ~25 µm across. Its nucleus, ~5 µm in diameter, contains 46 chromosomes with a total DNA length of 2 m. As we will see later, the packaging of DNA in eukaryotic chromosomes differs significantly from that in prokaryotic chromosomes.