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Red = extra from lecture Yellow Highlight = Teacher says is importantBlue Highlight = From ReviewKNOW THE DIFFERENCE: Lytic and lysogenic cycle pathways (virus video) Chapter 6: An Introduction to the Viruses Section 6.1: The Search for the Elusive Viruses The Search for the Elusive Viruses-Early Discoveries: Pasteur developed a vaccine for rabiesCoined the term “virus” (Latin for poison) Ivanovski and Beijernick: tobacco disease caused by a virus Loeffler and Frosch: foot-and-mouth disease caused by a virus -Filterable virus: Infectious fluids were passed through filters designed to trap bacteriaThe cell-free filtered fluid remained infectious This proved that an agent smaller than bacteria was the cause of disease *one of the largest viruses is smallpox – 200 nm = .2 micrometer*cells should not be smaller than 1.5 micrometer Concept Check: T/F: viruses can be cultured using the same methods as bacteria and fungi: false Pasteur developed a vaccine for the rabiesvirus Viruses were discovered by filtering infectious fluid through a filter designed to trap bacteriaSection 6.2: The Position of Viruses in the Biological Spectrum Viruses on the Biological Spectrum -Viruses can infect every type of cell: Bacteria -t4 e. coli Algae Fungi ProtozoaPlantsAnimals What is the Nature of Viruses? -Are they organisms? Are they alive? -What role did viruses play in the evolution of life? -What are their distinctive characteristics?
-How can a particle so small, simple, and seemingly insignificant be capable of causing disease and death? -What is the connection between viruses and cancer? -What role did viruses play in the development of all other organism? Unique Properties of Viruses-Infectious particlesRather than organisms -Active or inactive *virion (viruses outside the cell) Rather than alive or dead-Obligate intracellular parasites: Cannot multiply unless they invade a specific host cell Must instruct the genetic and metabolic machinery of the host cell to make and release new viruses Table 6.1: Properties of Viruses Are not cells Are obligate intracellular parasites of bacteria, protozoa, fungi, algae, plants, and animals Do not independently fulfill the characteristics of lifeAre inactive macromolecules outside the host cell and active only inside host cells Have basic structures of protein shell (Capsid) surrounding nucleic acid core Are ubiquitous in nature and have had major impact on development of biological lifeAre ultramicroscopic in size, ranging from 20 nm to 450 nm (diameter) Can have either DNA or RNA but not both Can have double-stranded DNA, sing-stranded DNA, single-stranded RNA, or double-stranded RNACarry molecules on surface that determine specificity for attachment to host cell Multiply by taking control of host cell’s genetic aterial and regulating the synthesis andassembly of new viruses Lack enzymes for most metabolic processes Lack machinery for synthesizing proteins Concept Check: T/F: viruses are alive: false