LS-MCRB 121 1st EditionExam # 3 Study Guide Chapters: 13-17 & 20Chapter 13: Viruses Viroids and PrionsGeneral Characteristics of Viruses- Viruses may be regarded as exceptionally complex aggregations of nonliving chemicals or as exceptionally simple living microbes- Viruses contain a single type of nucleic acid (DNA or RNA) and a protein coat, sometimes enclosed by an envelope composed of lipids, proteins, and carbohydrates- Viruses are obligatory intracellular parasites. o They multiply by using the host cell’s synthesizing machinery to cause the synthesis of specialized elements that can transfer the viral nucleic acid to other cellsHost Range- Host range: refers to the spectrum of host cells in which a virus can multiplyo Determined by the specific attachment site on the host cell’s surface and the availability of host cellular factors- Most viruses infect only specific types of cells in on host speciesViral Structure- Virion: A complete, fully developed viral particle composed of nucleic acid surrounded by a coat- Nucleic Acido Viruses contain either DNA or RNA, but never both, and the nucleic acid may be single or double-stranded, linear or circular, or divided into several separate molecules- Capsid and Envelopeo The protein coat surrounding the nucleic acid of a virus is called the capsid The capsid is composed of subunits, capsomeres, which can be a single type of protein or several types The capsid of some viruses is enclosed by an envelope consisting of lipids,proteins, and carbohydrateso Some envelopes are covered with carbohydrate-protein complexes called spikes- General Morphologyo Helical viruses resemble long rods and their capsids are hollow cylinders surrounding the nucleic acid Ebola viruso Polyhedral viruses are many-sided Adenoviruso Enveloped viruses are covered by an envelope and are roughly spherical but highly pleomorphic Influenza virus and simplexviruso Complex viruses have complex structures BacteriophagesTaxonomy of Viruses- Classification of viruses is based on type of nucleic acid, strategy for replication, and morphology- A viral species is a group of viruses sharing the same genetic information and ecological nicheIsolation, Cultivation, and Identification of Viruses- Viruses must be grown in living cells- The easiest viruses to grow are bacteriophagesViral Multiplication- Viruses don’t contain enzymes for energy production or protein synthesis- For a virus to multiply, it must invade a host cell and direct the host’s metabolic machineryto produce viral enzymes and componentsMultiplication of Bacteriophages- Lytic cycle: a phage causes the lysis and death of a host cell- Some viruses can either cause lysis or have their DNA incorporated as a prophage into the DNA of the host cell aka Lysogeny- Lytic Cycleo Attachment phase of lytic cycle: sites on the phage’s tail fibers attach to complementary receptor sites on the bacterial cello Penetration phase: phage lysozyme opens a portion of the bacterial cell wall, the tail sheath contracts to force the tail core through the cell wall, and phage DNA enters the bacterial cell. The capsid remains outsideo Biosynthesis: transcription of phage DNA produces mRNA coding for proteins necessary for phage multiplication.  Phage DNA is replicated and capsid proteins are producedo During the eclipse period, separate phage DNA and protein can be foundo Maturation: phage DNA and capsids are assembled into complete viruseso Release: phage lysozyme breaks down the bacterial cell wall and the new phages are released- Lysogenic Cycleo Prophage genes are regulated by a repressor coded for by the prophage The prophage is replicated each time the cell divides Exposure to certain mutagens can lead to excision of the prophage and initiation of the lytic cycleo Because of lysogeny, lysogenic cells become immune to reinfection with the same phage and may undergo phage conversiono A lysogenic phage can transfer bacterial genes from one cell to another through transduction Any genes can be transferred in generalized transduction and specific genes can be transferred in specialized transductionLatent Viral Infections- Latent viral infection: one in which the virus remains in the host cell for long periods without producing an infectiono Cold sores and shinglesPersistent Viral Infections- Persistent viral infections: disease processes that occur over a long period and are generally fatalo Caused by conventional viruses; viruses accumulate over a long periodPrions- Prions: infectious proteins first discovered in the 1980sChapter 14: Principles of Disease and Epidemiology- Pathogens: disease-causing microorganismsPathology, Infection, and Disease- Pathology is the scientific study of disease- Pathology is concerned with the etiology (cause), pathogenesis (development), and effectsof disease- Infection: the invasion and growth of pathogens in the body- Host: an organism that shelters and supports the growth of pathogens- Disease: an abnormal state in which part or all of the body is not properly adjusted or is incapable of performing normal functionsNormal Microbiota - Microorganisms begin colonization in and on the surface of the body soon after birth- Normal microbiota: microorganisms that establish permanent colonies inside or on the body without producing disease - Transient microbiota: microbes that are present for various periods and then disappearRelationships between the Normal Microbiota and the Host- Microbial antagonism: The normal microbiota can prevent pathogens from causing an infection- Three types of symbiosiso Commensalism: one organism benefits, the other is unaffectedo Mutualism: both organisms benefito Parasitism: one organism benefits, and one is harmedEtiology of Infectious Diseases- Koch’s Postulateso Koch’s postulates are criteria for establishing that specific microbes cause specificdiseaseso Requirements1. Same pathogen must be present in every case of the disease2. The pathogen must be isolated in pure culture3. The pathogen isolated from pure culture must cause the same diseasein a healthy, susceptible lab animal4. The pathogen must be reisolated from the inoculated lab animalExceptions to Koch’s Postulates- Koch’s postulates are modified to establish etiologies of diseases caused by viruses and some bacteria, which cannot be grown on artificial media- Some diseases, such as tetanus, have unequivocal signs and symptoms- Some diseases, such as pneumonia and