TheMcGraw-HillCompaniesChapter 6AnIntroductionFoundationsinto VirusesMicrobiologyEIGHTHEDTTIOKathleenParkTalaroBarryChessCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Chapter 6 An Introduction to Viruses Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
The Searchfor the Elusive Virus: Louis Pasteur postulated that rabies wascaused by a virus (1884) Ivanovski and Beijerinck showed a disease intobacco was caused by a virus (1890s): 1950s virology was a multifaceted discipline- Viruses: noncellular particles with a definitesize, shape, and chemical composition2
The Search for the Elusive Virus • Louis Pasteur postulated that rabies was caused by a virus (1884) • Ivanovski and Beijerinck showed a disease in tobacco was caused by a virus (1890s) • 1950s virology was a multifaceted discipline – Viruses: noncellular particles with a definite size, shape, and chemical composition 2
ThePositionofViruses intheBiological SpectrumCopyrightTheMcGraw-Hil Companes,ine.PemissionrquiredforreproductionordisplayThere is no universalTABLE6.1Properties of VirusesObligate intracellular parasitesofbacteria,protozoa,fungi,algaeagreement on how andplants,andanimalswhen viruses originated.Ultramicroscopic size.ranging from 20nm upto450nm(diameter)Viruses are considered.Not cellular in nature: structure is very compact and economical..Do not independently fulfill the characteristics of lifethe most abundant.Inactive macromolecules outside the host cell and active only insidemicrobes on earthhostcellsBasic structureconsists of protein shell (capsid)surroundingVirusesplayed arole innucleic acid core..Nucleic acid can beeitherDNA orRNAbut notboththe evolution of BacteriaNucleicacidcanbedouble-strandedDNA,single-stranded DNAArchaea, and Eukaryasingle-stranded RNA,or double-stranded RNA-Molecules on virus surface imparthigh specificity for attachmenttoVirusesareobligatehost cell..Multiply by taking control of host cell's genetic material andintracellularparasitesregulating the synthesis andassembly of new viruses.LackenzymesformostmetabolicprocessesLackmachineryforsynthesizingproteins3
The Position of Viruses in the Biological Spectrum • There is no universal agreement on how and when viruses originated • Viruses are considered the most abundant microbes on earth • Viruses played a role in the evolution of Bacteria, Archaea, and Eukarya • Viruses are obligate intracellular parasites 3
FEXGeneralSizeofVirusesSize range - most <0.2 μm; requires electronmicroscopeCopyright The McGraw-Hill Companies, nc. Permission required for reproduction or display.BACTERIALCELLSRickettsia0.3μmVirusesStreptococcus(1)E.coli1.Poxirus250nm1um2μmlong2.Herpessimplex150nm(10)125nm3.Rabies4.HV110nm(9)5.Influenza100nm6.Adenovrus75nm65nm7.T2bacteriophage30nm(2)8.Poliomyelitis(8)22nm9.YellowfeverProtein Molecule10.Hemoglobin15nmmolecule(7)(3)6(4)(5)4YEASTCELL-7μm
4 General Size of Viruses • Size range – most <0.2 μm; requires electron microscope YEAST CELL – 7 mm Streptococcus 1 mm Viruses 1. Poxvirus (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) 250 nm Protein Molecule 10. Hemoglobin molecule 15 nm 2. Herpes simplex 150 nm 3. Rabies 125 nm 4. HIV 110 nm 5. Influenza 100 nm 6. Adenovirus 75 nm 7. T2 bacteriophage 65 nm 8. Poliomyelitis 30 nm 9. Yellow fever 22 nm Rickettsia 0.3 mm E. coli 2 mm long BACTERIAL CELLS Copyright© The McGraw -Hill Companies, Inc. Permission required for reproduction or display
Viral Structure: Viruses bear no resemblance to cells- Lack protein-synthesizing machinery: Viruses contain only the parts needed to invadeand control a host cellCopyrightTheMcGraw-HilCompanies, Inc.Permission requiredforreproduction ordisplayCapsidEnvelope(notCoveringfound inall viruses)VirusparticleNucleicacidmolecule(s)(DNA or RNA)CentralcoreMatrixproteinsEnzymes(notfoundin5all viruses)
Viral Structure • Viruses bear no resemblance to cells – Lack protein-synthesizing machinery • Viruses contain only the parts needed to invade and control a host cell 5 Virus particle Capsid Envelope (not found in all viruses) Nucleic acid molecule(s) (DNA or RNA) Matrix proteins Enzymes (not found in all viruses) Covering Central core Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display
FEXGeneralStructureofViruses: CapsidsCopy right@ The McGraw-Hill Companies, Inc. Pemission requied forreproduction or display-All viruseshave capsids100(protein coats thatCapsidQO00OOenclose and protect theirnucleic acid)Nucleicacid- The capsid together withthe nucleic acid is the(a)NakedNucleocapsidVirusnucleocapsid- Some viruses have anEnvelopeexternal covering calledSpikee00009an envelope; thoselacking an envelope areCapsidnakedNucleic acid Each capsid is made ofidentical protein subunits6(b)EnvelopedViruscalledcapsomers
6 General Structure of Viruses • Capsids – All viruses have capsids (protein coats that enclose and protect their nucleic acid) – The capsid together with the nucleic acid is the nucleocapsid – Some viruses have an external covering called an envelope; those lacking an envelope are naked – Each capsid is made of identical protein subunits called capsomers (a) Naked Nucleocapsid Virus Nucleic acid Capsid (b) Enveloped Virus Envelope Spike Capsid Nucleic acid Copy right © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
GeneralStructureofVirusesCopyright The McGraw-HillCompanies, Inc. Permission required for reproduction or displayTwo structuralDiscscapsid types:Nucleic acidCapsomersQ9220208208282- Helical -continuous helix(a)of capsomersforming acylindricalnucleocapsid(b)-IcosahedralNucleic acidCapsidbeginsforming helix.(c)
7 General Structure of Viruses • Two structural capsid types: – Helical - continuous helix of capsomers forming a cylindrical nucleocapsid – Icosahedral Discs Capsomers (a) (b) (c) Nucleic acid Capsid begins forming helix. Nucleic acid Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display
FEXGeneralStructureof VirusesCopyightTheMeGrardisplayTwostructural(a) Ccapsid types:- Helical --Icosahedral Nuclei20-sided with 12corners08(d)
8 General Structure of Viruses • Two structural capsid types: – Helical - – Icosahedral - 20-sided with 12 corners Facet Vertex (a) Capsomers Nucleic acid (b) Capsomers Capsomers Vertex Fiber (c) (d) © Dr. Linda Stannard, UCT/Photo Researchers, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
FLEXGeneralStructureofVirusesCopy right @ The McGraw-Hill Companies, Inc. Permission required forreproduction or display. Viral envelope- Mostly animal virusesCapsidNucleocapsid- Acquired when theNucleic acidvirus leaves the hostcell(a)(b)Hemagglutinin spike-Exposed proteins onninidase spikethe outside of theMatrix proteinenvelope, calledLipid bilay erspikes, are essentialfor attachment of thevirus to the host cellNucleocapsid(c)50nmSpikesNucleocapsid9MuehcD(d)
9 General Structure of Viruses • Viral envelope – Mostly animal viruses – Acquired when the virus leaves the host cell – Exposed proteins on the outside of the envelope, called spikes, are essential for attachment of the virus to the host cell Capsid Nucleic acid Nucleocapsid (a) (b) Hemagglutinin spike Neuraminidase spike Matrix protein Lipid bilay er Nucleocapsid (c) 50 nm Spikes Nucleocapsid Dr. F. A. Murphy/CDC (d) © Dennis Kunkel/CNRI/Phototake Copy right © The McGraw-Hill Companies, Inc. Permission required f or reproduction or display
FunctionsofCapsid/EnvelopeCopy right @ The McGraw-Hill Companies, Inc. Permis sion required for reproduction or dis play .Protectsthe nucleicacidwhen the virus is outsideof the host cellHelps thevirusbindtoacell surface and assistsCapsomersilliams, JrJEPAthe penetration of the(a)Envelope CapsidDNAcoreviral DNA or RNA into asuitable host cell10(b)
10 Functions of Capsid/Envelope • Protects the nucleic acid when the virus is outside of the host cell • Helps the virus bind to a cell surface and assists the penetration of the viral DNA or RNA into a suitable host cell Capsomers (a) Fred P. Williams, Jr./EPA © Dr. Linda Stannard, UCT/Photo Researchers, Inc. Envelope Capsid DNA core © Eye of Science/Photo Researchers, Inc. (b) Copy right © The McGraw-Hill Companies, Inc. Permission required f or reproduction or display