Download Virus of Bacteria - Introduction to Biology - Lecture Slides and more Slides Biology in PDF only on Docsity! Chapter 13: Virus of Bacteria Docsity.com W ha t i s a P ha ge ? “The agents were called filterable viruses… Virus means ‘poison,’ a term that once had been applied to all infectious agents. With time, the adjective filterable was dropped and only the word virus was retained.” Bacteriophage were originally described as a macroscopic phenomenon that was slightly different from the “poisoning” of a plant or animal. Instead, what was observed was the destruction of a bacterial culture. People weren’t all that sure what a bacterium was so the destruction was seen more as an “eating” of the culture (by an otherwise unseen agent) rather than a poisoning. The filterable agent in this case was described as an “eater” of bacteria, or “Phage” from Greek: Bacteriophage = “Bacteria Eater.” “The word bacteriophage or phage that infect bacteria is both singular and plural when referring to one type of virus. The word phages is used when different types of phages are being referenced.” Docsity.com Vi ru s A rc hi te ct ur e Note spikes projecting from protein capsid surrounding nucleic acid. Note spikes projecting from lipid envelope- surrounding capsid (which in turn surrounds the nucleic acid). Docsity.com Vi rio n A tta ch m en t O rg an s Some virions are isometric: they have a fully symmetrical capsids, almost spherical. Isometric virions attach to cells via Attachment Proteins, a.k.a., Spikes which are proteins that symmetrically project from their virions. Spikes project from capsids in Naked viruses. Spikes project from envelopes in Enveloped viruses. Some virions are helical with attachment proteins at end or ends. Most phages have tailed virions which sort of combine the morphology of isometric and helical virions, with the isometric part called a head and the helical part called a tail. Attachment is made at the end of the tail opposite the head, and often is mediated by thin “feelers” called tail fibers. Docsity.com Vi ra l G en om es Nucleic-Acid Virus Genome ssDNA DNA dsDNA ssRNA dsDNA ssRNA (the retroviruses) Negative Positive dsRNA RNA ssRNA http://www.virology.net/Big_Virology/BVFamilyGenome.html One way to distinguish different types of viruses (e.g., influenza virus from HIV) is in terms of the characteristics of their nucleic-acid genomes. Docsity.com La te nt In fe ct io n S tra te gy For phages this is called Lysogeny. Only Temperate phages are able to display lysogeny. For phages this is called Lysogenic Conversion. Docsity.com Vi ra l I nf ec tio n S tra te gi es Docsity.com Te m pe ra te P ha ge L ife C yc le (s ) The prophage DNA can remain integrated indefinitely. This is a process called Induction. Docsity.com
