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Process of Reproduction in BacteriaBY: Amna Adnan | Category: Biology | Submitted: 2010-07-08 06:10:40
Article Summary: "Bacteria is a unicellular organism. It reproduces into two daughter cells by three processes that is conjugation, transduction and transformation. Plasmids, bacteriophages and DNA fragments are used during these processes..."
We are always surrounded by bacteria. They exist on earth in very large amounts and are playing their roles in the process of life. Some of them are beneficial and some are harmful for the humans, animals and plants. But the process of reproduction in both types of bacteria is the same that is binary fission. They reproduce into two daughter cells from one mother cell. Bacteria do not contain proper nucleus but their genetic material consists of a large circular chromosome which is attached to the bacterial cell wall. The replication of the chromosome occurs in the simple manner that it divides and makes two copies of chromosomes each passes in both daughter cells. The process of reproduction in bacteria is a continuous process in bacteria, it does not stop. Within 20 minutes, bacteria produce millions of daughter cells which are all identical to the mother cells. The genetic material transfers from mother to the daughter by vertical transmission.
When the process of horizontal transmission occurs in bacteria then beneficial mutations pass from one bacterial species to the other through three different phases that is conjugation, transduction and transformation. The transfer of genetic material in these phases occurs through plasmids, bacteriophages or genomic DNA sequences. Plasmid is a small circular DNA which is not part of the bacterial genetic material. A bacteriophage is actually a virus which attacks bacterial genetic material and transfers its own DNA into it. Genome DNA sequence is the genetic material of bacteria. When the genetic material is transferred into the bacterial cell, it either remains separated in the cell or becomes the part of the bacterial genetic material. This transfer of genetic material within bacterial species has allowed scientists to make different tools of molecular biology.
The process of conjugation starts when the two bacteria come together temporarily and exchange their genetic material in a friendly environment. This fusion of cells ad transfer of genetic material takes place through plasmids which are the source of transferring genes from donor cell to the recipient cell.
Process of conjugation was discovered in 1946 when a laboratory technician was performing an analytical test on bacteria. They discovered the F factor which is able to move between E.coli cells. F factor is actually a plasmid which is the source of transferring genetic material in bacterial species.
The process of conjugation starts with the mating between two cells. Once the stable mating is between the pair is formed then process of DNA replication starts. Due to the replication, a single stranded copy of Factor or plasmid produces unlike the normal mating in which double stranded DNA produces. This F factor is transferred into the recipient bacterial cell. The single stranded F factor when reaches the recipient cell, it copies to make double stranded DNA which is converted into a circular plasmid. At the end of the conjugation process, now recipient and donor cells both contain the similar copies of the F factor or plasmid. The recipient cell when mate with other cell, it will become donor and will transfer its new genes into the next cell. This is how the new genes are expressed in the bacterial cell. In some cases, instead of transferring of whole F factor, only the chromosomal genes can move to the recipient cell.
Process of transduction takes place through bacteriophage. This process was discovered in 1956 by Joshua Lederberg and Norton Zinder. In this process, the bacteriophage or virus injects its genetic material while killing the host cell and reproduces itself in the host cell. This is also called as Lytic cycle. It does not happen all the time. In some cases, when phage enters the bacterial cell, it does not kill the host cell but allows it to reproduce along with its own genetic material. This way the daughter cells get the genetic material of phage also. Some phages also make it possible to transfer the part of genetic material or plasmid between the bacterial cells.
Third form of bacterial reproduction is transformation. In this type, bacteria transfer their genetic material in the form of DNA. There are some bacteria which can transport free DNA from the outside into the bacterial cell. In this process, the double stranded DNA uses a protein receptor through which it binds to the surface of the recipient cell. It is possible that the sequences present in the outside DNA do not match the host cell's genetic material, then the outer DNA breaks down and its sequences are used to make new DNA during the replication process. It is thought that the DNA used in transformation is taken from other cells which release their genetic material. These cells are of the same population or specie.
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