BSC 160 1nd Edition Lecture 13 Outline of Last Lecture 1 Transcription 2 Sigma Factor 3 Regulation of Protein Synthesis Metabolism 4 Translation Outline of Current Lecture 1 Viruses 2 Virus Structures 3 Life of A Virus Current Lecture Chapter 13 Basic Virology A virus for every organism most abundant microbe Because viruses attack every domain prokaryotes eukaryotes viruses play big role in evolution of domains Problems being a virus Timing is everything Replicating so fast that you kill your host before spreading progeny Very narrow host range Virus is dependent on certain proteins in host If too narrow virus can be eradicated Mutations More genes you have easier for host to attack you Viruses have to coordinate reproductive cycle right proteins made at right times for assembly Properties of Viruses Obligate intracellular parasites do harm to host inside cell Microscopic in size Acellular not made up of cells Compact structure Do not independently fulfill characteristics of life Inactive macromolecules outside host cell active only inside host cell Basic structure Protein shell capsid surrounding nucleic acid core Nucleic acid can be either DNA or RNA not both Nucleic acid can be double stranded DNA single stranded DNA s strand RNA or dub strand RNA Molecules on virus surface impart high specificity for attachment to host cell Ability to take over the host cell s transcription translation enzymes Lack enzymes for most metabolic processes Lack machinery for synthesizing proteins Capsid Protein coat which protects nucleic acid can be multiple proteins or copies of single protein Protects from temperature environment Also plays role in delivery Nucleocapsid Nucleic acid capsid Enveloped Host cell plasma membrane wrapped around them Plyomorphic Peplomer Attachment Rod circle off membrane Naked viruses do not have envelopes just have capsid Primary Structures of Viruses 1 2 Proteins that make up acid are capsomers Icosohedral Simple Soccer ball shape nucleic acid inside 20 sided equilateral trianges Constrained Only certain size Example Adenovirus Helical cylindrical wrapped around nucleic acid Phage Virus that infects bacteria Enveloped Viruses that attacks animals Complex Viruses Atypical Genome Can be DNA or RNA Single or double stranded Each virus will contain only one type Nuclear Proteins Present inside capsid with nucleic acid Functions Viral maturation entrance into new host DNA RNA Replicases Reverse transcriptase Viruses are not motile Random collision Move by heat of system until bump into appropriate host Life Cycle of a Virus Attachment Adsorption Bind to molecule on host to gain entry Early Phase Entry Penetrate Whole capsid doesn t have to enter cell o Have to uncoat
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