Читать книгу Cell Biology - Stephen R. Bolsover - Страница 69

The chromosome of the bacterium E. coli is a single circular DNA molecule of about 4.6 × 10⁶ base pairs. It has a circumference of 1 mm, yet must fit into the 1 μm cell so, like eukaryotic chromosomes, it is coiled, supercoiled, and packaged with basic proteins that are similar to eukaryotic histones. However, an ordered nucleosome structure similar to the “beads on a string” seen in eukaryotic cells is not observed in prokaryotes. Prokaryotes do not have nuclear envelopes so the condensed chromosome, together with its associated proteins, lies free in the cytoplasm, forming a mass that is called the nucleoid to emphasize its functional equivalence to the eukaryotic nucleus.