TRANSDUCTION

Transduction is the process by which bacterial DNA is moved from one bacterium to another by a virus. It was first discovered by Joshua Lederberg in 1952. The most striking feature is the transfer of genetic material from cell to cell by viruses. The second feature is the fact that only a small part of the total genetic material of any one bacterial cell is carried by any particular transducing particle.

I. The bacteriophages (viruses that infect bacteria) infect a bacterial cell. Their normal mode of reproduction is to harness the DNA replication machinery of the host bacterial cell and make numerous copies of their own DNA or RNA. These copies of bacteriophage DNA or RNA are then packaged into newly synthesized copies of bacteriophage v Hons.

  1. However, the packaging of bacteriophage DNA is not fool-proof Small pieces of bacterial DNA also pack into a bacteriophage virion instead of the bacteriophage genome. Viruses with RNA genomes are not able to package DNA and so don’t usually make this mistake.
  2. These virions come out on lysis of the host cell. The mispackaged virions containing bacterial DNA can attach to other bacterial cells. They inject the DNA they have packaged. Thus they transfer the bacterial DNA from one cell to another. This DNA can become part of the new bacterium’s chromosome.

Type of Transduction

It has three forms:

(a)Generalized transduction: It occurs in lytic cycle of phage virus. DNA of phages virus enter into E.coli bacteria. This DNA replicates and develops many new DNA and capsids. The DNA of bacteria is broken. Some pieces of DNA also enter into capsid of virus. Bacteria burst and release new phage viruses. Now this phage enters into recipient bacteria and transfer DNA of donor bacteria into the DNA of recipient bacteria. Bacterial endo nucleases enzymes destroy the phage virus. Now these bacteria incorporate genes of donor bacteria and replicates.

(b)Specialized transduction: It occurs in Lysogenic cycle of phage virus.

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           Fig: Transduction


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In this cycle viral DNA incorporate into bacterial DNA as prophage. ‘t remains peacefully there. But sometime, it becomes lytic. It conies out of bacterial DNA. Some part of bacterial DNA remain attach with it. Viral DNA with a piece of bacterial DNA replicates andlops new capsids. Bacteria burst. Virus infects
other bacteria and transfer genes of donor bacteria to recipient bacteria.

(c) Restricted transaction: Certain phages carry out a more restricted kind of transduction. They carry only a specific section of bacterial genetic material. They transduce only a few genes. Retroviruses carry out specific or restricted transduction. These viruses can cause the formation of tumors (oncogenesis) in animals. It is now known that these viruses exchange a small portion of their genome for a mutant cellular gene that has a role in gene regulation or replication. These viruses carrying mutant genes infect cells. They transform these cells into tumor cells.

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