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