Like a human cell, a dividing bacterium needs to copy its DNA. Unlike human cells, which have multiple linear (rod-like) chromosomes enclosed in a membrane-bound nucleus, bacterial cells usually have a single, circular chromosome and always lack a nucleus. However, the bacterial chromosome is found in a specialized region of the cell called thenucleoid.
Copying of DNA by replication enzymes begins at a spot on the chromosome called the origin of replication. The origin is the first part of the DNA to be copied. As replication continues, the two origins move towards opposite ends of the cell, pulling the rest of the chromosome along with them. The cell also gets longer, adding to the separation of the newly forming chromosomes.
Stages of binary fission.
Replication continues until the entire chromosome is copied and the replication enzymes meet at the far side. Once the new chromosomes have moved to opposite cell ends and cleared the center of the cell, division of the cytoplasm can take place.
In this process, the membrane pinches inward and a septum, or new dividing wall, forms down the middle of the cell. (Bacteria have a cell wall, so they must regenerate this wall when they undergo cell division.)
Finally, the septum itself splits down the middle, and the two cells are released to continue their lives as individual bacteria.
Copying of DNA by replication enzymes begins at a spot on the chromosome called the origin of replication. The origin is the first part of the DNA to be copied. As replication continues, the two origins move towards opposite ends of the cell, pulling the rest of the chromosome along with them. The cell also gets longer, adding to the separation of the newly forming chromosomes.
Stages of binary fission.
- We see the intact bacterial chromosome (which is circular). It has two regions called the origin of replication and the terminus of replication, which are located diametrically opposite to one another on the chromosome.
- The chromosome opens at the origin of replication, and the two DNA strands are copied, with replication proceeding in opposite directions on the two strands.
- Copying continues, and the cell elongates. The new origins of replication move apart, towards opposite ends of the cell.
- A septum (wall) forms down the middle of the cell, partitioning it into two new cells, each with one of the two (now-complete) bacterial chromosome copies.
- The cell pinches in two. We now have two new bacteria!
Replication continues until the entire chromosome is copied and the replication enzymes meet at the far side. Once the new chromosomes have moved to opposite cell ends and cleared the center of the cell, division of the cytoplasm can take place.
In this process, the membrane pinches inward and a septum, or new dividing wall, forms down the middle of the cell. (Bacteria have a cell wall, so they must regenerate this wall when they undergo cell division.)
Finally, the septum itself splits down the middle, and the two cells are released to continue their lives as individual bacteria.
