BIOLOGY 207 1st Edition Lecture 9 Outline of Previous Lecture I. Mutations and mutagenesisII. Gene transfer in bacteriaIII. CRISPR interferenceOutline of Current Lecture I. Nature of virusesII. Lytic vs. LysogenicCurrent LectureGenetics of VirusesI. Nature of Virusesa. Viron: consists of nucleocapsid (capsid [protein coat] with nucleic acid)i. Two main categories of viron1. Naked2. Enveloped b. Viral genomes come in different typesi. DNA or RNAii. Single or double strandiii. Linear or circulariv. Plus sense or minus sense (for single stranded genomes)c. Viruses can infect anything that it can make a hosti. Bacteria 1. Viruses that affect bacteria are called bacteriophages)These 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.ii. Archaeaiii. Animal cellsiv. Plant cellsv. Protists d. Lysis/Lytic virusesi. Involve virus replication leading to the destruction of the host cellii. The host metabolism is redirected, supporting the virus replication and development; eventually the virus bursts the host cell due to replication and then the new virons go on to infect other cellse. Lysogenic virusesi. More long term infectionii. Viral genome integrates itself into the host genomeiii. The genetic alteration by the phage to the host does not destroy it, but creates a cell that serves the virus’ needsf. 5 steps of viral replicationII. Lytic vs. Lysogenica. T4- lytic infectioni. “Head-and-tail” bacteriophage, meaning that it has both helical and icosahedral symmetry1. Icosahedral head; linear DNA; complex tailii. ~300 proteins encoded by genome1. Encodes 8 of its own tRNA (differing from E. coli, which it infects)iii. Attachment occurs with proteins on the virus and cell receptors on the host1. Receptors must be present on the host for viral attachment2. These can be different types of receptors- they are not virus specific; rather they perform other functions for the cell, but are receptive to viruses as well3. Can use different cell receptors for attachment iv. T4 lysozyme forms a hole in the peptidoglycan layerv. During penetration, the tail contracts and T4 DNA in injected into the host, leaving the capsid behindvi. T4 must modify its DNA to evade being ejected or destroyed by the host1. CRISPR defense mechanism protects the cell from viral attacks2. The virus DNA is modified to match that of the host, so it appears to be harmless, when in reality it is just in an altered formvii. The entire time it takes from start to finish for T4 to undergo transcriptionand translation in the cell is about 30min1. After only 1min, the host cell stops synthesizing its own DNA/RNA and the phage gene begins to undergo transcription2. Within 4min, phage DNA replication begins3. Since T4 doesn’t have its own RNA polymerase, it requires the host cell’s- it modifies the RNA polymerase so that the phage promoters are recognized and the host genes are not viii. Protein synthesis involves translation of:1. Early proteinsa. Process initiation; protect viral genome; mediate the virus’ own functions2. Middle proteinsa. RNA polymerase-modifying enzymes; used to express the genes3. Late proteinsa. Structural and release proteins; package viral DNA and burst cellb. Lambda phage- lysogenyi. Long term relationship between host and virus; temperate virusii. Lysogen: host cell that harbors the temperate virusiii. Prophage: viral DNA in host celliv. Lysogenetic state maintained by phage-encoded repressor proteinc. Difference between lytic and lysogenic