Microbiology chp 5 notes PDF

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micro chp 5 notes 5.1 virus Microscopic, acellular agent composed of nucleic acid surrounded by a protein coat. 5.2 capsid The protein covering of a virus's nucleic acid core. Capsids exhibit symmetry due to the regular arrangement of subuniis called capsomers. See icosahedron. nucleocapsid In viruses, the close physical combination of the nucleic acid with its protective covering. virion An elementary virus particle in its complete morphological and thus infectious form. A virion consists of the nucleic acid core surrounded by a capsid, which can be enclosed in an envelope. capsomere A subunii of the virus capsid shaped as a mangle or disc. helical capsid Protein covering of viruses made of rod-shaped capsomeres that form a coiled nucleic acid/capsid structure. Icosahedron A regular geometric figure having 20 surfaces that meet to form 12 corners. Some virions have capsids that resemble icosahedral crystals. enveloped virus A virus whose nucleocapsid is enclosed by a membrane derived in part from the host cell. It usually contains exposed glycoprotein spikes specific for the virus. genome The complete set of chromosomes and genes in an organism. Genomic libraries Collections of DNA fragments representing the entire genome of an organism inserted into plasmids and stored in vectors such as bacteria or yeasts. genomics The systematic study of an organism's genes and their functions. 5.3

Adsorption- a process of adhering one molecule onto the surface of another molecule penetration (viral) The step in viral multiplication in which virus enters the host cell. uncoating The process of removal of the viral coat and release of the viral genome by its newly invaded host cell. synthesis (viral) The step in viral multiplication in which viral genetic material and proteins are made through replication and transcription/ translation. Assembly (viral)- the step in viral multiplication in which capsids and genetic material are packaged into virions release The final step in the multiplication cycle of viruses in which the assembled virus particle exits the host cell and moves on to infect another cell. host range The limitation imposed by the characteristics of the host cell on the type of virus that can successfully invade it. cytopathic effect The degenerative changes in cells associated with virus infection. Examples: the formation of multinucleate giant cells (Negri bodies), the prominent cytoplasmic inclusions of nerve cells infected by rabies virus. provirus The genome of a virus when it is integrated into a host cell's DNA. transformation In microbial genetics, the transfer of genetic material contained in "naked" DNA fragments from a donor cell to a competent recipient cell. oncovirus Mammalian virus capable of causing malignant tumors. Bacteriophage- a virus that specifically infects bacteria lyse To burst.

temperate phage A bacteriophage that enters into a less virulent state by becoming incorporated into the host genome as a prophage instead of in the vegetative or lytic form that eventually destroys the cell. prophage A lysogenized bacteriophage; a phage that is latently incorporated into the host chromosome instead of undergoing viral replication and lysis. lysogeny The indefinite persistence of bacteriophage DNA in a host without bringing about the production of virions. induction The process whereby a bacteriophage in the prophage state is activated and begins replication and enters the lytic cycle. lysogenic conversion A bacterium acquires a new genetic trait due to the presence of genetic material from an infecting phage. 5.4 plaque In virus propagation methods, the clear zone of lysed cells in tissue culture or chick embryo membrane that corresponds to the area containing viruses. In dental application, the filamentous mass of microbes that adheres tenaciously to the tooth and predisposes to caries, calculus, or inflammation. 5.5 prion A concocted word to denote "proteinaceous infectious agent"; a cytopathic protein associated with the slow-virus spongiform encephalopathies of humans and animals. viroid An infectious agent that, unlike a virion, lacks a capsid and consists of a closed circular RNA molecule. Although known viroids are all plant pathogens, it is conceivable that animal versions exist. virome The complete array of viruses in a given ecosystem, such as the human body.

Chapter Summary 5.1 The Position of Viruses in the Biological Spectrum • Viruses are noncellular entities whose properties have been identified through technological advances in microscopy and tissue culture. • Viruses are infectious particles that invade every known tYpe of cell. They are not alive, yet they are able to redirect the metabolism of living cells to reproduce virus particles. • Viruses have a profound influence on the genetic makeup of the biosphere. • The International Committee on the Taxonomy of Viruses oversees naming and classification of viruses. Viruses are classified into orders, families, and genera. • Viruses are grouped in various ways. This textbook uses their structure, genetic composition, and host range to categorize them. 5.2 The General Structure of Viruses • Virus size range is from 20 to 1,500 nm (diameter). Viruses are composed of an outer protein capsid enclosing either DNA or RNA plus a variety of enzymes. Some viruses also possess an envelope around the capsid. • Spikes on the surface of the virus capsid or envelope are critical for their attachment to host cells. 5.3 Modes of Viral Multiplication • Viruses go through a multiplication cycle that generally involves adsorption, penetration (sometimes followed by un- coating), viral synthesis and assembly, and viral release by lysis or budding. • These events turn the host cell into a factory solely for making and shedding new viruses. This results in the ultimate destruction of the cell. • Animal viruses can cause acute infections or can persist in host tissues as chronic latent infections that can reactivate periodically throughout the host's life. Some persistent animal viruses can cause cancer. • Bacteriophages vary significantly from animal viruses in their methods of adsorption, penetration, site of replication, and method of exit from host cells. • Lysogeny is a condition in which viral DNA is inserted into the bacterial chromosome and remains inactive for an extended period. The viral DNA is replicated with the chromosome every time the bacterium divides.

• Some bacteria express virulence traits that are coded for by the bacteriophage DNA in their chromosomes. This phenomenon is called lysogenic conversion. 5.4 Techniques in Cultivating and Identifying Animal Viruses • Animal viruses must be studied in some sort of living cell or tissue. • Cell and tissue cultures are cultures of host cells grown in special sterile chambers using aseptic techniques to exclude unwanted microorganisms. • Virus growth in cell culture and bacteriophage growth on bacterial lawns are detected by the appearance of plaques. 5.5 Other Noncellular Infectious Agents • Other noncellular agents of disease are the prions, which are not viruses at all but protein fibers; viroids, extremely small lengths of naked nucleic acid; and satellite viruses, which require the presence of larger viruses to cause disease. 5.6 Viruses and Human Health • Viruses are easily responsible for several billion infections each year. It is conceivable that many chronic diseases of unknown cause will eventually be connected to viral agents. • Viral infections are difficult to treat because the drugs that attack viral replication also cause side effects in the host....