Lecture 13 Outline of Last Lecture 1. Transcription2. Sigma Factor3. Regulation of Protein Synthesis & Metabolism4. TranslationOutline of Current Lecture 1. Viruses2. Virus Structures3. Life of A VirusCurrent LectureChapter 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 domainsProblems 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 assemblyProperties 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 BSC 160 1nd Edition- Lack enzymes for most metabolic processes- Lack machinery for synthesizing proteinsCapsid- Protein coat which protects nucleic acid; can be multiple proteins or copies of single protein- Protects from temperature, environmentAlso plays role in delivery- Nucleocapsid= Nucleic acid + capsidEnveloped- Host cell plasma membrane wrapped around them. Plyomorphic. - Peplomer- Attachment; Rod & circle off membrane. Naked viruses do not have envelopes, just have capsidPrimary Structures of Viruses- Proteins that make up acid are capsomers 1. Icosohedral- Simple. Soccer ball shape, nucleic acid inside- 20 sided, equilateral trianges- Constrained. Only certain size- Example: Adenovirus2. Helical- cylindrical, wrapped around nucleic acid- Phage- Virus that infects bacteriaEnveloped Viruses- that attacks animalsComplex Viruses- Atypical. Genome- Can be DNA or RNA- Single or double stranded- Each virus will contain only one typeNuclear Proteins- Present inside capsid with nucleic acidFunctions: Viral maturation & entrance into new host: DNA/RNA/Replicases/Reverse transcriptaseViruses 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 cello Have to
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