Lecture 4_ Ch 29.5-29.6 General Properties of Viruses.pdf

Chapter 29.5-29.6: General Properties of Viruses Jawetz, Melnick, & Adelberg’s Medical Microbiology Twenty-Eighth Edition...

Chapter 29.5-29.6: General Properties of Viruses Jawetz, Melnick, & Adelberg’s Medical Microbiology Twenty-Eighth Edition Stefan Riedel Slides by Dr. Jose Sapien Jawetz, Melnick, & Adelberg’s Medical Microbiology, Twenty-Eighth Edition  29.5: Principles of Virus Structure Types of Symmetry of Virus Particles Symmetry of the capsid is important in classifying viruses a. Cubic/Icosahedral b. Helical c. Complex Image credit: PPT - VIRUS STRUCTURE AND CLASSIFICATION PowerPoint Presentation, freedownload -ID:2274975 (slideserve.com) © McGraw-Hill Education, 2019  The particular structural features of each virus family are determined by: The functions of the virion Morphogenesis and release from infected cells Transmission to new hosts Attachment, penetration, and uncoating in newly infected cells. © McGraw-Hill Education, 2019 29.5: Principles of Virus Structure A. Cubic Symmetry 20 faces & 12 vertices 60 viral identical subunits → 60 structural units → capsids. Form independently of the nucleic acid Both RNA and DNA viruses can have cubic symmetry capsids All cubic symmetry observed with animal viruses is of the icosahedral pattern, the most efficient arrangement for subunits in a closed shell. Example: Adenovirus © McGraw-Hill Education, 2019 Zhuang, X., et al. (2022) © 2021 John Wiley & Sons, Inc. © McGraw-Hill Education, 2019  29.5: Principles of Virus Structure B. Helical Symmetry Proteins that make the capsid are bound to the nucleic acid and wind it into a helix shape Nucleocapsid is coiled within the envelope Unlike the cubic symmetry, there are not empty helical particles forming separate from the nucleic acid © McGraw-Hill Education, 2019 29.5: Principles of Virus Structure C. Complex Structures Do not have cubical or helical shape, but can vary. Example: Poxviruses have a unique structure (brick shaped). © McGraw-Hill Education, 2019 29.5: Principles of Virus Structure Measuring the Sizes of Viruses Electron microscopes most common for estimating size. Viruses can be visualized in preparations from tissue extracts and in ultrathin sections of infected cells. Must coat the virus in heavy metal. Sedimentation in an ultracentrifuge can be used by looking at rates of sedimentation and particle density © McGraw-Hill Education, 2019  29.6: Chemical Composition of Viruses Viral Proteins serve many functions Main purpose: move the viral genome into the host & enzymes for replication Protect from inactivation by nuclease Help attach virus to potential host cells Structural symmetry of capsid Proteins = antigenic characteristics © McGraw-Hill Education, 2019  Example of antigenic characteristics of the virus: H1N1 Influenza A virus Some surface proteins may also exhibit specific activities (eg, influenza virus hemagglutinin agglutinates red blood cells). © McGraw-Hill Education, 2019 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10892522/ © McGraw-Hill Education, 2019  Example of proteins as enzymes: RNA polymerase carried by negative sense, single strand RNA viruses like orthomyxoviruse © McGraw-Hill Education, 2019  29.6: Chemical Composition of Viruses Viral Nucleic Acid Only contain one form of nucleic acid (RNA or DNA) contains the genetic information Can be single stranded, double stranded, segmented, linear or non segmented DNA RNA Genome size: 3.2kbp-375 kbp Genome size: 4 kb-32 kb Linear or circular Linear, segmented configuration Double or single strand Double or single strand A kilobase pair is a unit of length of nucleic acids = 1000 base pairs. The term 'kilobase' ( kb ) is commonly used interchangeably, but technically this refers to a single-stranded nucleic acid. © McGraw-Hill Education, 2019 29.6: Chemical Composition of Viruses Viral Lipid Envelopes Some viruses have envelopes surrounding the capsid Envelope is made of lipids It forms when the maturing nucleocapsid buds through the cell membrane Can only happen at sites where specific proteins are in the host cell membrane Budding process varies depending on the replication and nucleocapsid © McGraw-Hill Education, 2019 29.6: Chemical Composition of Viruses Viral Lipid Envelopes Example: Influenza Note: viruses with lipid envelopes may be more susceptible to being disrupted by certain solvents and therefore reduce infection © McGraw-Hill Education, 2019 © McGraw-Hill Education, 2019 29.6: Chemical Composition of Viruses Viral Glycoproteins Glycoproteins: Are envelope embedded proteins for attaching the virus particle to cell receptors of host cell Also involved in membrane fusion and act as viral antigens. They can prevent neutralization of the virus with specific antibodies © McGraw-Hill Education, 2019  29.6: Chemical Composition of Viruses Viral Glycoproteins Examples: On the surface of influenza, hemagglutinin (HA) and neuraminidase (NA) are made of polypeptides Viruses | Free Full-Text | Competitive Cooperation of Hemagglutinin and Neuraminidase during Influenza A Virus Entry (mdpi.com) © McGraw-Hill Education, 2019 Questions? © McGraw-Hill Education, 2019