MMG301 1st Edition Lecture 21Outline of Last Lecture I. BacteriaOutline of Current Lecture II. VirusesIII. BacteriophagesCurrent Lecture-virus: a DNA or RNA genetic element surrounded by a protein coat capable of replicating in cells as a parasite and exists in a free state -virion: virus particle-bacteriophage: bacterial virus (aka phage)-characteristics of viruses-obligate parasites: only replicate in host cells-contain a genome surrounded by a protective protein coat that allows this genome to be transmitted from one host organism to another; host can be eukaryotic or procaryotic(mostly bacteria, a few archaea)-exists in two states:-extracellular- nucleic acid surrounded by proteins (and sometimes a membrane):termed a virion or virus particle-intracellular- where the virus genome is introduced into the host cell (called infection) and replicates itself-viruses can contain either DNA or RNA in a circular or linear form, or go through DNA and/or RNA intermediates during their life cycle-inner core of nucleic acid: can be single or double stranded, single or multiple segments, circular or linear, DNA or RNAThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-capsid: protein coat surrounding nucleic acid-proteins assemble in subassemblies called capsomers-capsomers aggregate into protein coat-the entire capsid + nucleic acid = nucleocapsid-complex viruses: composed of separate subassemblies which then assemble into virus-example: T4 bacteriophage-lysis: host cell destruction, does not happen for all viruses-titer: virus concentration-plaque: clear zone on agar plate-bacteriophage lambda: two pathways of existence – lytic and lysogenic-lysogeny: incorporation of phage genome into the host E. coli genome to form a latent state called a prophage-a lysogen (cell containing prophage) is immune to infection by the same virus-induction: excision of viral genome from the host genome – cell then follows a lytic pathway-retrovirus life cycle1. entry by fusion of envelope with cell membrane2. uncoating of virion to release ssRNA3. reverse transcription4. travel to nucleus; integration into host genome5. integration of DNA into host genome6. transcription of viral DNA to make RNA genome copies and mRNA7. encapsidation8. budding and
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