Conjugation

Topic: Genetics Of Prokaryotic Cells

Conjugation is the transfer of genetic material between two bacterial cells in direct contact.

Conjugation is one of the three modes of genetic transfer in prokaryotes in which two bacteria transfer genetic material by direct contact. In conjugation, cell to cell contact is required so that DNA can be transferred from one bacterial cell to another. Bacterial pili are responsible for bringing the cells, a donor and a recipient, into contact with one another. Donor cells contain an F plasmid; they are sometimes called F+ cells. The recipient cell that receives the plasmid is called an F- cell. The DNA transferred can be in the form of a plasmid, a small circular piece of extrachromosomal DNA, or as a hybrid, containing both plasmid and chromosomal DNA.

During typical conjugation, the pilus brings the two cells into contact. A single-stranded copy of the plasmid is transferred through to the recipient cell, which then synthesizes the complementary strand, making it double-stranded. The F cell now becomes an F+ cell capable of making its own pili. Eventually, in a mixed bacterial population containing both F+ and F cells, all cells will become F+ cells.

Conjugation. Conjugation of the F plasmid from an F+ cell to an F cell is brought about by the conjugation pilus bringing the two cells into contact. A single strand of the F plasmid is transferred to the F cell, which is then made double-stranded.

 

 

Practice Questions

 

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Key Points

• Conjugation is a type of prokaryotic reproduction in which DNA is transferred between prokaryotes utilizing a pilus.

• Typical conjugation of the F plasmid from an F+ cell to an F cell is brought about by the conjugation pilus bringing the two cells into contact. A single strand of the F plasmid is transferred to the F cell, which is then made double-stranded.


Key Terms

conjugation: transfer of DNA through direct contact using a conjugation pilus

pilus: a hairlike appendage found on the cell surface of many bacteria

prokaryotes: an organism whose cell (or cells) are characterized by the absence of a nucleus or any other membrane-bound organelles

plasmid: a small circular piece of extrachromosomal DNA,

F plasmid:  contains genes that allow the plasmids DNA to be transferred between cells

complementary strand: a section of one nucleic acid chain that is bonded to another by a sequence of base pairs



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