Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 76

So far, we have discussed the details of DNA replication, but we have not discussed how bacterial DNA as a whole is replicated, nor have we discussed how the replication process is coordinated with division of the bacterial cell. To simplify the discussion, we first consider only bacteria that grow as individual cells and divide by binary fission to form two cells of equal size, even though this is far from the only type of multiplication observed among bacteria.

Figure 1.13 Physical blocks on template DNAs. (A) When DNA polymerase III stalls on the lagging-strand template strand, a new Okazaki fragment can be initiated and the stalled polymerase can be moved to the new RNA primer. The process leaves a gap that must be repaired by other means, probably involving RecFOR (see chapter 9). (B) When DNA polymerase III stalls on the leading strand, primase can restart DNA replication, leaving a gap that must be repaired by other means. (C) In some cases where DNA polymerase III stalls at damaged DNA, translesion polymerase can utilize the same sliding clamp to replicate through the lesion, often by error-prone DNA replication. The translesion polymerases have low processivity and fall off the template after a short distance, allowing the accurate DNA polymerase III replication to resume high-fidelity DNA replication.

The replication of the bacterial DNA occurs during the cell division cycle, which is the time during which a cell is born, grows larger, and divides into two progeny cells. Cell division is the process by which the larger cell splits into the two new cells. The division time, or generation time, is the time that elapses from the point when a cell is born until it divides. This time is usually approximately the same for all the individuals in the population under a given set of growth conditions. The original cell before cell division is called the mother cell, and the two progeny cells after division are called the daughter cells.