exam iv willoughby notes

exam iv willoughby notes - Chapter 13 The Genetics of...

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The Genetics of Viruses and Prokaryotes Probing the Nature of Genes Prokaryote/virus advantages for study of genetics: small genomes quickly produce large numbers of progeny usually haploid (easier genetic analyses) prokaryotes are tools for biotechnology and cell research prokaryotes are important ecologically some prokaryotes and viruses are pathogens Viruses: Reproduction and Recombination Most viruses are composed of a nucleic acid and a few proteins. Viruses are acellular (noncellular) and do not metabolize energy. viruses are made of nucleic acid and protein – some also have additional molecule types they are acellular (noncellular) and do not metabolize energy or produce ATP the first virus discovered was the tobacco mosaic virus in the 1950s, electron microscopes showed how much viruses differ from bacteria the simplest infective agents are viroids , made up only of nucleic acid (they are not viruses) Viruses are obligate intracellular parasites reproduce using the host’s synthetic machinery, often destroying host cell in the process Virion genetic material is either DNA or RNA and is surrounded by protein capsid characteristic shapes determined by capsid viruses are unaffected by antibiotics because they lack the structures and biochemistry of bacteria Viruses are described using four criteria: genome: DNA or RNA nucleic acid: single-stranded or double-stranded shape: simple or complex whether or not the virion is surrounded by a membrane Viruses that infect bacteria are bacteriophages . like other viruses, they recognize host by specific binding between capsid proteins and host cell receptor proteins the virions have “tail” assemblies that inject the nucleic acid into the host cell Two types of virus reproductive cycles: lytic cycle – reproduce immediately and kill the host cell lysogenic cycle – postpone reproduction by integrating its nucleic acid into host cell genome Lytic cycle: infected bacterium lyses, releasing progeny virions those that only have lytic cycles are called virulent viruses virus nucleic acid takes over the host’s synthetic machinery in two stages early stage: viral genes adjacent to the virus promoter are transcribed - late stage: viral genes code for the protein coat and an enzyme that causes host cell lysis for viral release Lysogenic cycle : host cell does not lyse, but harbors the viral nucleic acid for many generations bacteria harboring phage that are not lytic are called lysogenic bacteria . the viruses are called
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exam iv willoughby notes - Chapter 13 The Genetics of...

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