Viruses and Prions(Chapter 13)Lecture MaterialsforAmy Warenda Czura, Ph.D.Suffolk County Community CollegeEastern CampusPrimary Source for figures and content:Tortora, G.J. Microbiology An Introduction 8th, 9th, 10th ed. San Francisco: PearsonBenjamin Cummings, 2004, 2007, 2010.Amy Warenda Czura, Ph.D.1SCCC BIO244 Chapter 13 Lecture SlidesVirus: Latin for “poison”-discovered as “contagious fluid”-obligate intracellular pathogen-contains few enzymes of its own-must get most enzymes and all biomoleculebuilding blocks and energy from host cellCharacteristics of a virus:1. contains a single type of nucleic acid: eitherDNA or RNA but not both2. has a protein coat (capsid) surrounding thenucleic acid, some also have a lipid envelope around the capsid3. multiply inside living cells by using the synthesizing machinery of the host cell4. cause the synthesis of specialized viral structures that can transfer the viral nucleicacid to other cells5. have a specific host rangeAmy Warenda Czura, Ph.D.2SCCC BIO244 Chapter 13 Lecture SlidesHost range = the spectrum of host cells typesthe virus can infect-viruses are usually specific to a single species(or even strain) of host-a virus has molecules on its surface that specifically adhere to some molecule on the host cell surface, each virus is specialized to attach to and infect one typeof cell-in multicellular hosts viruses usually infect only certain specific cell types in that speciese.g. HIV: human T helper cells-host range is determined by the virus requirements for attachment and entry intothe cell and the availability of of host factors necessary for viral replicationAmy Warenda Czura, Ph.D.3SCCC BIO244 Chapter 13 Lecture SlidesViral Size-must be smaller than the cells they infect: 20-1,000nm in length-smaller than bacteria (E. coli 1000 x 3000nm)-too small to be seen by light microscopyAmy Warenda Czura, Ph.D.4SCCC BIO244 Chapter 13 Lecture SlidesViral StructureVirion = infectious viral particle:completely assembled with a protein coatsurrounding the nucleic acid1. Nucleic Acid:- either RNA or DNA, but not both- single or double stranded- linear or circular- if RNA, it can be plus/sense strand (has codons) or minus/antisense (need to makecomplement sense strand for translation)-2,000 to 250,000 nucleotides(E. coli → 4 million, human → 3 billion)2. Capsid = protein coat-composed of subunits called capsomeresAmy Warenda Czura, Ph.D.5SCCC BIO244 Chapter 13 Lecture Slides-some capsids have protein-carbohydrate pointed projections called pentons-if pentons are present they areused for attachment to thehost cell3. Envelope (not all viruses)-some viruses have an envelope around the capsid consisting of lipids, proteins and carbohydrates (cell membrane like)-with envelope = enveloped virus-if a virus does not have an envelope it is called a non-enveloped virus-the envelope may be coded for by the virus ortaken from the host cell plasma membrane-some envelopes havecarbohydrate-protein complexes calledspikes which areused for attachmentto the host cellAmy Warenda Czura, Ph.D.6SCCC BIO244 Chapter 13 Lecture Slidesinteresting note:-Coronavirus (cold) and influenza virus (flu)have high mutation rate in spike genes-by changing the spikes, they can evade the host immune system-you get infected by colds and the flu over andover since each one with slightly differentspikes looks completely new to your immune systemAmy Warenda Czura, Ph.D.7SCCC BIO244 Chapter 13 Lecture SlidesMorphologyThe capsid architecture can be distinct and sometimes identifies a particular virus1. Helical-cylindrical capsid-made up of a helicalstructure of capsomereswith the nucleic acidwound up inside e.g. Rabies virus, Ebola virushttp://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/t045/T045376A.jpgAmy Warenda Czura, Ph.D.8SCCC BIO244 Chapter 13 Lecture Slides2. Polyhedral-most are icosahedrons:20 equilateral triangle faces & 12 corners-may have pentonse.g. Adenovirus,Polio virusPoliovirusAmy Warenda Czura, Ph.D.9SCCC BIO244 Chapter 13 Lecture Slides3. Enveloped Viruses-appear spherical due tothe lipid envelope, but contain a shaped capsid:Enveloped helicale.g. influenza virusEnveloped polyhedrale.g. Herpes Simplex Virus-may have spikeshttp://www.bact.wisc.edu/themicrobialworld/hsv1struc.jpghttp://www.zephyr.dti.ne.jp/~john8tam/main/Library/influenza_site/influenza_virus.jpgHerpes simplex virusInfluenza virusAmy Warenda Czura, Ph.D.10SCCC BIO244 Chapter 13 Lecture Slides4. Complex Viruses-unique shapee.g. bacteriophage: capsid & accessory structurese.g. pox virus: no clear capsid, just several protein layers around the nucleic acidAmy Warenda Czura, Ph.D.11SCCC BIO244 Chapter 13 Lecture SlidesTaxonomy-a viral “species” is a group of viruses sharingthe same genetic information and the sameecological niche (host range)-species names are not used; usually viruses are just given a Genus name (ends in ‘virus’) and a common nameViruses are grouped into families (names endin ‘-viridae’) based on:1) Nucleic acid type2) Strategy for replication3) MorphologyViruses are more commonly identified by theircommon name – learning the family groups has little relevance to disease ID.e.g.Family: HerpesviridaeGenus: SimplexvirusHerpes Simplex Virus 2 (HSV2)(Also known as HHV-2: human herpesvirus 2)Amy Warenda Czura, Ph.D.12SCCC BIO244 Chapter 13 Lecture SlidesChart of families – Table 13.2Note all the various possibilities:-Single stranded DNA, non-enveloped-Double stranded DNA, non-enveloped-Double stranded DNA, enveloped-Single stranded RNA, plus strand,non-enveloped-Single stranded RNA, plus strand, enveloped-Single stranded RNA, minus strand, enveloped-Single stranded RNA, minus strand,non-enveloped-Multiple strand RNA, minus strand, enveloped-Double strand RNA, non-enveloped-Double strand RNA, envelopedViruses are more commonly identified by theircommon name – learning the family groups has little relevance to disease ID.Amy Warenda Czura, Ph.D.13SCCC BIO244 Chapter 13 Lecture SlidesAmy Warenda Czura, Ph.D.14SCCC BIO244 Chapter 13 Lecture Slidesenvelopednon-envelopedenvelopedDoublestrandRNA envelopedAmy Warenda Czura, Ph.D.15SCCC BIO244 Chapter 13 Lecture SlidesCultivation of viruses for study:-viruses must be grown in living cells, usuallytheir specific host-viruses cannot be grown in culture media alone (obligate intracellular parasites)Three ways to grow animal viruses in lab:1. Animal Models-infect live animals with the viruspositive