Session 13 (Viruses and Prokaryotes)

Session 13 (Viruses and Prokaryotes) - MCB 181 Study...

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MCB 181 Study Session 13 (Viruses and Prokaryotes) “Big fleas have little fleas, upon their backs to bite 'em, And little fleas have lesser fleas, and so, ad infinitum.”
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Learning Goals for Study Session 13 (Viruses and Prokaryotes) Be able to describe the general structures of viruses and the mechanisms they employ for reproduction. Distinguish between the lytic and lysogenic cycle employed by phages. Briefly describe the unique reproductive features of retroviruses. Be able to describe the difference between transformation, transduction, conjugation and how they contribute to genetic recombination in bacteria. Understand the difference between a chromosome and a plasmid and the role of each in the genetics of bacteria. Briefly describe transposable genetic elements and the role they play in creating genetic variation in bacteria. Be able to describe the structural features of bacterial operons and to specifically describe the lac and trp operons as examples of inducible and repressible operons, respectively.
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Viruses and bacteria have unique genetic mechanisms that allow them to survive in a changing environment! A virus has a genome but can reproduce only within a host cell. Their reproduction usually weakens or destroys the host cell leading to viral diseases suffered by plants, animals and other organisms. Bacteria , as representatives of prokaryotes are remarkable in their ability to reproduce rapidly and utilize a vast array of substance as sources of energy and nutrients. Viroids (circular RNA molecules of only several hundred nucleotides) and prions (misfolded form of a protein that appears to cause normal proteins to also misfold) are the simplest known agents that can cause disease. In this study session we consider the genetic mechanisms used by viruses and bacteria to reproduce. Information about viroids and prions is not presented, but is available in the textbook.
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Viruses are not living cells! Viruses are much smaller than the smallest bacterium and typically consist of just nucleic acid and a few proteins. Viruses enter cells and use the host cells capabilities for DNA replication and protein synthesis to reproduce themselves. The release of new virus particles from the host cell commonly results in its death. The term virion is used to refer to individual virus particles outside the host cell. A virion consists of a central core of either DNA or RNA surrounded by a protein capsid, and sometimes a membrane envelope . As shown to the right, viruses are diverse and classified by the type of genome (DNA or RNA; single or double stranded), complexity of structure, and whether surrounded by a membrane.
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Viruses are obligate intracellular parasites! Bacteriophages (or simply
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This note was uploaded on 03/24/2010 for the course MCB 181 taught by Professor Jorstad during the Spring '07 term at University of Arizona- Tucson.

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Session 13 (Viruses and Prokaryotes) - MCB 181 Study...

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