Reproduction And Recombination

Prokaryotes usually reproduce by binary fission, which is a form of asexual reproduction. During binary fission, shown in Figure 23-11, the DNA replicates and the two daughter DNA molecules are pulled to opposite ends of the cell. Finally, the cell membrane pinches in two to form two identical daughter cells.

Prokaryotes can exchange pieces of DNA that can be added to the cell's DNA without reproduction. This process is called recombination. Prokaryotes can get DNA from other prokaryotes in three ways: transformation, bacterial conjugation, and transduction. Transformation occurs when a prokaryote takes in DNA from its outside environment. Conjugation is the process by which two prokaryotes bind together and one cell transfers DNA to the other cell through a structure called a sex pilus. In transduction, a virus obtains a small part of DNA from a host prokaryote. The virus then copies itself inside the host, and new copies of the prokaryotic DNA are made with the viral DNA. After the new viruses have been released, they carry the prokaryotic gene to the next prokaroyote.

Understanding these methods of bacterial genetic exchange is of great importance to our understanding of genetics. Transformation provided the evidence that DNA is the genetic material of cells. Investigations on the process of conjugation gave scientists key information about the mechanisms of genetic recombination common to all organisms. Transformation is used every day in thousands of labs to transfer bits of human and other DNAs into bacterial cells to identify and isolate certain genes. The sequencing of the human genome, one of the greatest feats in history, relied on recombining human genes into artificial plasmids and artificial chromosomes called bacterial artificial chromosomes (BACs). The BACs and plasmids were then inserted into bacterial cells by transformation. The results of such studies are being used to develop a better understanding of human health and to find improved treatment for disease.

DNA in the prokaryotic cell is copied.

DNA in the prokaryotic cell is copied.

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