Study Guide Test 3

Study Guide Test 3 - Bio Test #3 Chapter 34: Viruses...

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Bio Test #3 Chapter 34: Viruses Viruses are obligate, intracellular parasites that have no phylogenic tree but can evolve Influenza outbreak in 1918-1919: “Spanish Flu”: most devastating epidemic Viruses use many structural motifs; 4 most common: helical (rods), polyhedrons, spheres, and complex shapes with heads and tails o Bacteriophages have the most complex capsids. HIV causes disease from helper T cells and macrophages being affected; kills indirectly o Current infected: 38 million with 5 million added each year o Env: gene for glycoproteins; gag: gene for capsid components; pol: gene for reverse transcriptase, integrase, protease; tat: gene for regulatory protein that speeds transcription of provirus Both vaccines and antiviral drugs are 2 goals of researchers in this “nanobiology” Viruses can either be enclosed by just a shell of protein called a capsid or enclosed by both a capsid and a membrane-like envelope (from the host cell) Most lysogenic viruses affect bacteria. If a bacterium is growing and dividing rapidly, then a virus’s fitness is maximized through lysogenic; if it is likely to stop growing or die, then the fitness is maximized through lytic growth. Envelope proteins are synthesized in rough ER, finished in Golgi (carbohydrates added), and attached to cell’s membrane; membrane becomes viral membrane when exiting. Core proteins are synthesized by ribosomes in the cytoplasm. Nonenveloped and enveloped differ in entry to cell: Non- inserts genome while capsid remains on outside membrane or wall; the entire capsid enters the cell for enveloped. Membrane protein CD4 was the “doorknob” to HIV; also coreceptors CXCR4 and CCR5 Retroviruses: reverse-transcribe DNA genome from RNA strand through reverse transcriptase into sscDNA and into dsDNA. Protease from the virus cuts polypeptide sequences into functional proteins to be used for production of viral proteins. Exiting: most budding viruses infect host cells without a cell wall; most viruses that burst infect host cells that do have a cell wall. Positive sense virus: genome contains same sequences as the mRNA required to produce viral proteins Negative sense virus: base sequences in the genome are complementary to those in viral mRNAs In ambisense virus, some sections are positive sense while others are negative sense Viruses’ origin o Escaped genes hypothesis: Viruses probably came from plasmids and transposable elements, as they are differentiated only by the presence of a protein/ membrane-like coat or envelope. o Degeneration hypothesis: DNA viruses may have descended from bacteria living in cells that degenerated by losing the genes to synthesize ATP, nucleic acids, amino acids, etc.
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Grouped into 70 families by structure of virion and nature of host species. o
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Study Guide Test 3 - Bio Test #3 Chapter 34: Viruses...

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