Prokaryotes divide by fission
1. Prokaryotic cells grow in size, replicate DNA, and divide into two new cells. This
process is called fission.
2. Escherichia coli (a bacterium) simply divides as quickly as resources permit. At 37oC, this is about once every 40 minutes. When resources are abundant, E. coli can divide every 20 minutes.
3. Prokaryotes generally have just one circular chromosome.
• The E. coli chromosome is 1.6 mm in diameter, making the unfolded circle 100
times greater than the size of the cell. The molecule is packaged by folding in on
itself with the aid of basic proteins that associate with the acidic DNA.
• Circular chromosomes appear to be characteristic of all prokaryotes.
4. The prokaryotes have a site called ori, where DNA replication begins, and a site ter, where it ends.
• Ori is short for origin of replication.
• Ter is short for terminus of replication.
5. As DNA replicates, each of the two resulting DNA molecules attaches to the plasma membrane. As the bacterium grows, new plasma membrane is added between the attachment points, and the DNA molecules are moved apart.
6. Cytokinesis, which is cell partitioning, begins around 20 minutes after chromosome duplication is completed. A pinching of the plasma membrane to form a constricting ring separates the one cell into two, each with a complete chromosome.
• A tubulin-like fiber is involved in the purse-string constriction.
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