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