BIO 2200 Lecture Notes Exam 3.docx

For most people an asymptomatic vaccine is available

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For most people, an asymptomatic vaccine is available: recommended at 12 yrs old Circular dsDNA genome; 8 kbp Viruses using Reverse Transcriptase Retroviruses: have RNA genomes Hepadnaviruses: have DNA genomes Characteristics of Reverse transcriptase: o Performs reverse transcription (RNA-dependent DNA polymerase) o Replication: DNA dependent DNA polymerase o RNase H: Degrades RNA when it is paired to DNA or DNA/ RNA duplexes o Makes errors in replication every 1/10000 (10 -4 ) nucleotides (high mutation rate)
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Retroviruses (+) ss RNA viruses that replicate through a DNA intermediate Enveloped viruses Contain a reverse transcriptase, integrase, and protease Virion contains specific tRNA molecules (act as primer for replication) HIV/AIDS ~37 million people living with HIV infection worldwide o 70% in Sub-Saharan Africa o 1.2 million people in US living with HIV infection 39 million people have died from AIDS related illnesses since epidemic began o 1.2 people died in 2014; 2 million new cases of AIDS in 2014 HIV infects and kills T-cells (CD4) o Causes immunodeficiency disease (AIDS) o Body can’t find other diseases → death from opportunistic diseases and infection related cancers No cure and no vaccine; antiretroviral therapy (ART) significantly extends life and quality of life
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Retroviruses have a unique genome o Two identical ssRNA molecules of the plus (+) orientation o Contain specific genes gag: encode structural proteins pol: encode reverse transcriptase and integrase env: encode envelope proteins Plant RNA Viruses Most plant viruses are positive-strand RNA viruses
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o Example: tobacco mosaic virus, first virus identified Gain entry through wounds in leaf Genomes can move within the plant host through intercellular connections that span the cell walls Subviral Agents: Viroids and Prions Viroids: infectious RNA molecules that lack a protein coat o Smallest known pathogens (246–399 bp) o Cause a number of important plant diseases o Small, circular, ssRNA molecules o Do not encode proteins; completely dependent on host-encoded enzymes Prions: infectious proteins whose extracellular form contains no nucleic acid o Resistant to very high heat (>600 C) o Known to cause disease in animals (transmissible spongiform encephalopathies) “Mad cow disease” in cows (Bovine spongiform encephalopathy; BSE)-- 1980’s outbreak in UK Scrapie in sheep Creutzfeld-Jakob (CJD) in humans vCJD from consuming cows with BSE “kuru” in Papua New Guinea tribes practicing mortuary o Host cell contains gene (PrnP) that encodes native form of prion protein that is found in healthy animals o Prion misfolding results in neurological symptoms of disease (e.g., resistance to proteases, insolubility, and aggregation) Chapter 10: Genetics of Bacteria and Archaea Mutations and Mutants Mutation : a heritable change in DNA sequence that can lead to a change in phenotype (observable properties of an organism)
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