Читать книгу Cell Biology - Stephen R. Bolsover - Страница 15

One of the major distinctions between prokaryotic and eukaryotic cells is their mode of division. In prokaryotes the circular chromosome is duplicated from a single replication origin by a group of proteins that reside on the inside of the plasma membrane. At the completion of replication the old and new copies of the chromosome lie side by side on the plasma membrane which then pinches inwards between them. This process, which generates two equal, or roughly equal, daughter cells is described as binary fission. In eukaryotes the large, linear chromosomes, housed in the nucleus, are duplicated from multiple origins of replication by enzymes located in the nucleus. Sometime later the nuclear envelope breaks down and the replicated chromosomes are compacted so that they can be segregated without damage during mitosis. We will deal with mitosis in detail in Chapter 14. For the moment we should be aware that although it is primarily about changes to the nucleus, mitosis is accompanied by dramatic changes in the organization of the rest of the cell. A new structure, the mitotic spindle, is assembled specifically to move the chromosomes apart whilst other structures are dismantled so that their components can be divided among the two daughter cells following cell division.