what is the lambda of bacteriphage
Answers
Answer:
Enterobacteria phage λ (lambda phage, coliphage λ, officially Escherichia virus Lambda) is a bacterial virus, or bacteriophage, that infects the bacterial species Escherichia coli (E. coli). It was discovered by Esther Lederberg in 1950. The wild type of this virus has a temperate life cycle that allows it to either reside within the genome of its host through lysogeny or enter into a lytic phase, during which it kills and lyses the cell to produce offspring. Lambda strains, mutated at specific sites, are unable to lysogenize cells; instead, they grow and enter the lytic cycle after superinfecting an already lysogenized cell.
The phage particle consists of a head (also known as a capsid), a tail, and tail fibers (see image of virus below). The head contains the phage's double-strand linear DNA genome. During infection, the phage particle recognizes and binds to its host, E. coli, causing DNA in the head of the phage to be ejected through the tail into the cytoplasm of the bacterial cell. Usually, a "lytic cycle" ensues, where the lambda DNA is replicated and new phage particles are produced within the cell. This is followed by cell lysis, releasing the cell contents, including virions that have been assembled, into the environment. However, under certain conditions, the phage DNA may integrate itself into the host cell chromosome in the lysogenic pathway. In this state, the λ DNA is called a prophage and stays resident within the host's genome without apparent harm to the host. The host is termed a lysogen when a prophage is present. This prophage may enter the lytic cycle when the lysogen enters a stressed condition.
Answer:
Mature particles of bacteriophage lambda are composed of about equal amounts of protein and DNA. Each phage contains one double-stranded DNA molecule encapsulated in an icosahedral head, which is about 50 nm (0.05 μ) in diameter; a flexible tubular tail, which is about 150 nm (0.15 μ) long and terminates in a fiber, projects from the head (Kellenberger and Edgar, 1971). Lambda is an obligatory parasite of Escherichia coli. Growth begins when a phage particle attaches to the host by the tip of its tail and injects its DNA molecule. Lambda is a temperate phage and, thus, can multiply in E. coli by one of three ways: (1) In productive growth, the injected DNA molecule directs the synthesis of numerous gene products; these promote replication of the phage DNA, synthesis of the phage heads and tails, packaging of the DNA into mature phage particles, and eventual lysis of the cell. At 37°C it takes about 40 minutes for a lytic cycle, and about 100 infective progeny phage are produced. (2) Lambda DNA can also persist in the host cell as a prophage and replicate passively as an integral part of the bacterial genome. In this case the injected DNA must first direct the synthesis of the gene products that promote its linear insertion into the genome of the host. Next, it turns on the synthesis of the repressor, which blocks transcription of those genes responsible for autonomous lambda DNA replication and most other phage functions.
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