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Day_8_-_Bacteriophage - Lytic Bacteriophages Development...

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1. There is a need for new types of antimicrobial therapies. 2. 100 million bacteriophages in environment: sequences are untapped. 3. Reservoir of information for genomics for all biology. 4. Complexity of biology argues for return to experimentation on model systems such as specific bacteriophages. 5. High school science teaching should be inquiry-based. 6. Phage provide opportunities for experimentation. 7. Therefore, need new influx of researchers into field of bacteriophage research. Why phage matter in the 21 st century Bruce Alberts, 1993 – 2005 President of the National Academy of Sciences Lytic Bacteriophages: Development, Genetics, and Generalized Transduction
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Viruses that infect bacteria are called BACTERIOPHAGE (eaters of bacteria). Bacteriophages are NOT considered to be ALIVE because they can not multiply on their own. This point can be argued because they can reproduce after they infect a cell (obligate parasite – so are some bacteria). Bacteriophages are infectious particles: 1. they have relatively small nucleic-acid genomes , either DNA or RNA, single-stranded or double-stranded. 2. Their genomes are packaged in protein or membrane coat ( capsid ) for protection. Bacteriophages usually are identified by the Greek letter φ followed by letters and/or numbers . Examples: φ T4 , φ 29 , φ N4 . However, the φ often is omitted; e.g., T4 , λ , N4. Bacteriophage
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Phages differ in their complexity : φ MS2 has only four genes and a capsid that consists of only two different types of proteins, whereas φ T4 has a genome that includes about 200 genes and has a capsid that consists of at least 20 different proteins, some being represented in as many as 1000 copies . Electron micrographs Phage from Enterococccus sp. Bacteriophages from E. coli T4 λ Bacteriophage diversity Plaques M13 T3 Fig. 7.1 RNA phage MS2
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Lytic cycle of bacteriophages Lytic bacteriophages infect bacteria, go through the lytic cycle. Within less than an hour, 200-400 progeny are released from the infected cell, which then infect neighboring cells. On an agar surface, this results in a plaque at a site where an infected cell was located in a lawn of uninfected cells
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T4 phage particle Fig 7.8
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Bacteriophage T4 Bacteriophage T4 (phage T4)
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An artist’s perception of lysis Bacteriophage infection DNA injection by a T-even bacteriophage
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Bacteriophage multiplication: the lytic cycle After the phage injects its DNA , the early genes are transcribed and translated . Most early genes encode products involved in phage transcription and replication . Then DNA replication begins , and the late genes are transcribed and translated to form the head and tail of the phage. The DNA is packaged into the heads ; the tails are attached , then cells lyse , releasing the phage to infect other cells. Fig 7.2
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Regulatory Cascade One or more gene products synthesized during each stage of development regulates expression of genes in the next stage Fig 7.3 2 early regulatory genes (activators) 1 middle activator 1 middle repressor 1 late repressor
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Regulatory genes Regulatory genes are identified by 1.
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