- Hfr cell
An hfr cell (also called hfr strain) is a
bacteriumwith a conjugative plasmid(often F) integrated into its genomic DNA. Hfr is the abbreviation for "high frequency recombination", which was first characterized by Luca Cavalli-Sforza. Unlike a normal F+ cell, hfr strains will, upon conjugation with a F− cell, attempt to transfer their "entire" DNA through the mating bridge, not to be confused with the pilus. This occurs because the F factor has integrated itself via an insertion point in the bacterial chromosome. Due to the F factor's inherent nature to transfer itself during conjugation, the rest of the bacterial genome is dragged along with it, thus making such cells very useful and interesting in terms of studying gene linkage and recombination. Because the genome's rate of transfer through the pilus is constant, molecular biologists and geneticists can use Hfr strain of bacteria (often " E. coli") to study genetic linkage and map the chromosome. The procedure commonly used for this is called interrupted mating. A bacterium may undergo conjugation. During this process, genetic material is transferred to another bacterium through the mating bridge. Piliare often incorrectly believed to transfer DNA, but these structures are simply used to bring mating bacteria close enough to form a mating bridge. To form pili, an F plasmid is required. The F plasmid consists of around 25 genes which are mostly required for the production of the pilus. F+ denotes cells that contain the F plasmid, while F− cells do not. The F plasmid is considered to be an episomewhich may become integrated into the main chromosome. When the F genes become integrated into the chromosome, the cell is said to be Hfr (high frequency of recombination). An Hfr cell may transfer F genes to an F− cell. During this transfer of genetic material, the F episome may take chromosomal DNA with it. The donor cell does not lose any genetic material as anything transferred is also replicated concurrently. It is extremely rare that an Hfr cell's chromosome is transferred in its entirety. Homologous recombinationoccurs when the newly acquired DNA crosses over with the homologousregion of its own chromosome.
A structure as fragile as a mating bridge will, however, likely break, and so the transfer is rarely complete. Thus, the F− cell uses only part of the genomic DNA of the Hfr cell for recombination. Though there is some debate on the issue, the pili themselves do not seem to be the structures through which the actual exchange of DNA takes place; rather, some proteins seem to open a channel between the bacteria.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Hfr strain — A bacterial strain that donates its genes with high frequency to a recipient cell during conjugation because the F factor is integrated into the bacterial chromosome … Dictionary of microbiology
HFR — high frequency recombination * * * high frequency of recombination; see under cell … Medical dictionary
Hfr — heart frequency; high frequency * * * high frequency of recombination; see under cell … Medical dictionary
List of topics in cell biology — Cell invokes a major branch of theory and research known variously as cell biology, cellular biology or cytology. The study of cell tissues is known as histology. Cell types are often referred to using the suffixes blast, clast, cyte, especially… … Wikipedia
Outline of cell biology — Light micrograph of a moss s leaf cells at 400X magnification. The following outline is provided as an overview of and topical guide to cell biology: Cell biology (formerly cytology, from the Greek kytos, container ) – academic discipline that… … Wikipedia
Merozygote — is a state when a cell, usually bacterial, is temporarily diploid as result of DNA transfer processes like conjugation. One example of how merozygotes can be formed is the transfer of genetic material during an HFR transformation. In HFR… … Wikipedia
episome — episomal, adj. episomally, adv. /ep euh sohm /, n. Genetics. bacterial DNA that is extrachromosomal and that may replicate autonomously as a plasmid or become incorporated into the chromosome and replicate with it. [1930 35; EPI + SOME3] * * *… … Universalium
List of biochemistry topics — This page aims to list articles on Wikipedia that are related to biochemistry. This is so that those interested in the subject can monitor changes to the pages by clicking on .This list is not necessarily complete or up to date if you see an… … Wikipedia
List of biology topics — Biology is the study of life and its processes. Biologists study all aspects of living things, including all of the many life forms on earth and the processes in them that enable life. These basic processes include the harnessing of energy, the… … Wikipedia
Neutron Capture Therapy of Cancer — Neutron Capture Therapy (NCT) is a noninvasive therapeutic modality for treating locally invasive malignant tumors such as primary brain tumors and recurrent head and neck cancer. It is a two step procedure: first, the patient is injected with a… … Wikipedia