BIOL 209 1st Edition Lecture 7Outline of Last Lecture I. Question/Answer’sII. Protein Transport & SecretionIII. DigestionIV. Energy AcquisitionV. Cytoskeletal StructuresA. MicrofilamentsB. MicrotubulesC. Assembled MicrotubulesVI. FungiA. Fungal PathogensB. Yeasts and MoldsVII. ProtozoaOutline of Current Lecture I. Question/Answer’sII. Classes of Viral StructuresIII. Viral Genomes – Diverse Structures IV. Viral GrowthV. Viral ReplicationA. Steps1. Absorption – binding to cell surface receptors2. & 3. Entry/Uncoating4. Synthesis of viral components5. Assembly of new virus6. Release of virusCurrent LectureI. Question/Answer’sA. Question: What is a virus? Answer: A small infectious microbe that replicates only inside host cells of other living organismsB. Question: Can you name some viruses? Norovirus, HIV, HPV, rhinovirus, Ebola, small poxC. Question: How do viruses compare to other microbes in size, composition, and location? Answer: They are the smallest microbe besides prions, they are composed of all four types of macromolecules, and they are located everywhereThese 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.D. Question: Which of the following processes are carried out by an isolated virus? Answer: None of the above… A virus can’t carry out any life processes without a host cellE. Question: Viral genomes are composed of? Answer: DNA (single and double stranded)and RNA (single and double stranded)F. Question: Virus genomes are only a tiny fraction of the size of a cell genome, yet viral reproduction requires synthesis of all the same complex macromolecules as cellular reproduction. How do viruses do it? Answer: They use host cell’s abilities to their own advantage by getting the cells to do work for themG. Question: Why do cells have receptors for viruses? Answer: *Trick question! Cells have receptor proteins designed to do a specific job, and the virus borrows the receptor for its own benefitII. Classes of Viral Structures: Naked, Enveloped, and ComplexA. All have genomes coated with protein – a “capsid” polymer – to create a nucleocapsid1. May also include accessory proteins – enzymes particular for that virus’ replication (naked structure)2. Enveloped structures have a membrane that surrounds the nucelocapsid3. Complex structures (ex. pox viruses & bacteriophages) have unique structuresIII. Viral Genomes – Diverse StructuresA. Viral genomes are either DNA or RNA – the nucleic acid can be either single or double strandedB. Usually the genomes are either circular or a single linear ‘chromosome’1. Some viral genomes are packaged as separate segmentsC. Size varies, but they are generally very smallIV. Viral GrowthA. Typically kills the host cell; either by cell lysis and release of new virions or by 'budding' from host cell membranes (enveloped viruses)1. Each infected cell releases large numbers of virus particles a. The extremely high rate of reproduction allows viruses to evolve very quicklyV. Viral ReplicationA. Steps1. Adsorption – binding to cell surface receptorsa. Viruses attach to cell surfaces through interactions between viral proteins and specific cell surface receptors - Enveloped viruses bind cell receptors using glycoproteins in the envelope - Naked viruses use capsid proteinsb. The ability of a virus to infect a cell is limited by whether the host cell expresses the appropriate receptor - Each virus has a specific 'host range'2. & 3. Entry/Uncoatinga. Entry mechanisms differ depending on the virus- Enveloped virus structures enter through either fusion or endocytosis - Naked virus structures enter through endocytosis only- Bacteriophages, such as T phages, bind to specific receptors on the cell envelope and directly inject their genomes into thehost cell4. Synthesis of viral componentsa. Virus controls host cell function to promote 1) viral genome replication and 2) viral protein productionb. Location of genome replication depends upon the virus - DNA viruses replicate in the nucleus - RNA viruses replicate either in the nucleus or cytoplasm, depending on the virus5. Assembly of new virusa. Replicated viral genomes are packaged by interaction with capsid proteins to create nucleocapsids6. Release of virusa. Enveloped viruses are released from the cytoplasmic or nuclear membrane b. Newly synthesized viral glycoproteins (spikes) are inserted in the membrane to create the viral envelope - Once bound by assembled nucleocapsids, the region buds off releasing the virusc. Non-enveloped viruses assemble into nucleocapsids, accumulate within the cell, and are released upon cell