Microbiology - Week 8 - Lecture 1 - Virology PDF

INTRODUCTION TO VIROLOGY H I S TO R Y, D I V E R S I T Y A N D TA XO N O M I C S Prepared by: Nick Inglis, Ph.D. BMS 100 Week 7 WHAT IS A VIRUS? Nucleic acid(s) surrounded by a coat of protein Cannot reproduce or carry out metabolic activities outside of a host cell Significant due to effects on hum...

INTRODUCTION TO VIROLOGY H I S TO R Y, D I V E R S I T Y A N D TA XO N O M I C S Prepared by: Nick Inglis, Ph.D. BMS 100 Week 7 WHAT IS A VIRUS? Nucleic acid(s) surrounded by a coat of protein Cannot reproduce or carry out metabolic activities outside of a host cell Significant due to effects on human health AND contributions to molecular biology research Beijernick (1898) Tobacco Mosaic Disease 1 Extracted sap from tobacco plant with tobacco mosaic disease 2 Passed sap through a porcelain filter known to trap bacteria THE DISCOVERY OF VIRUSES (LATE 1800S) 4 Healthy plants became infected 3 1935: WENDELL STANLEY ACTUALLY SEES THE TOBACCO MOSAIC VIRUS Crystallized the virus and then performed Xray crystallography. Crystallization: the process of getting a soluble structure out of solution and getting a precipitate for analysis ELECTRON MICROSCOPY REVEALS THE ACTUAL STRUCTURE TERMINOLOGY Capsid – protein coat surrounding nucleic acid Capsomere – protein subunit of the capsid Nucleocapsid – viral nucleic acid surrounded by its capsid Viral envelope – membrane surrounding nucleocapsid INFECTIOUS CYCLE / VIRAL REPLICATION 1.Attachment 2.Entry 3.Translation of viral mRNA & viral genome replication 4.Assembly 5.Release 1 Attachment LYTIC CYCLE OF PHAGE T4 Lysogenic cycle “Virulent” phage Attachment Bacteriophage genome Tail sheath Outer membrane Peptidoglycan Cytoplasmic membrane 1 Attachment LYTIC CYCLE OF PHAGE T4 Entry 2 Entry of phage DNA and degradation of host DNA 1 Attachment LYTIC CYCLE OF PHAGE T4 2 Entry of phage DNA and degradation of host DNA 3 Synthesis of viral genomes and proteins 1 Attachment LYTIC CYCLE OF PHAGE T4 2 Entry of phage DNA and degradation of host DNA Phage assembly 4 Assembly 3 Synthesis of viral genomes and proteins Head Tail Tail fibers 1 Attachment LYTIC CYCLE OF PHAGE T4 5 Release 2 Entry of phage DNA and degradation of host DNA Phage assembly 4 Assembly 3 Synthesis of viral genomes and proteins Head Tail Tail fibers Phage head Tail sheath Tail fiber Bacterial cell 100 nm DNA PHAGE LAMBDA “Temperate” phage Attachment Lambda phage Prophage in chromosome Entry Lytic cycle Lysogeny Synthesis Release Assembly Replication of chromosome and virus; cell division Induction Excision of viral DNA from chromosome Triggered by UV light, carcinogens, X-rays Further replications and cell divisions DIFFERENT TYPES OF CELL CULTURE USED IN VIROLOGY Monolayer CELL CULTURE IN VIROLOGY: 1. PRIMARY CELL CULTURES CELL CULTURE IN VIROLOGY: 2. CONTINUOUS CELL LINES HeLa cells L cells 3T3 cells CELL CULTURE IN VIROLOGY: 3. SUSPENSION CULTURES CYTOPATHIC EFFECTS Polio DEVELOPMENT OF CYTOPATHIC EFFECTS Cell rounding and lysis Murine leukemia virus Syncitium formation GROWTH OF VIRUSES IN EMRYONATED EGGS LABORATORY ANIMALS FOR VIRAL PROPAGATION ASSAY OF VIRUSES: PLAQUE FORMATION Photomicrograph of a single plaque created by rabies on kidney cells Polio on HeLa CALCULATING VIRUS TITER FROM THE PLAQUE ASSAY PFU = Plaque forming units CLASSIFYING VIRUSES: THE CLASSICAL SYSTEM Nature of the nucleic acid in virion (DNA/RNA) Symmetry of the protein shell (Capsid) Presence of absence of a lipid membrane (Envelope) Dimensions of the virion and the capsid Orders (3); Families (73); Subfamilies (9); Genera (287); Species (1950) RNA VIRAL SHAPES: 1. HELICAL - E.g. Tobacco Mosaic Virus Capsomere of capsid 18  250 nm 20 nm (a) Tobacco mosaic virus DNA VIRAL SHAPES: 2. POLYHEDRAL Capsomere - Often icosahedral (20 sided) - E.g. Common cold adenovirus Glycoprotein 70–90 nm (diameter) 50 nm (b) Adenoviruses Head VIRAL SHAPES: 3. COMPLEX VIRUSES E.g. Bacteriophages (phages) Smallpox DNA Tail sheath Tail fiber 80  225 nm Rabies 50 nm (d) Bacteriophage T4 Membranous envelope RNA Capsid VIRAL ENVELOPES - Steal host membranes to make envelopes - Viruses with envelopes called enveloped virion - Viruses without – naked virions Glycoproteins 80–200 nm (diameter) 50 nm (c) Influenza viruses VIRAL SIZE E. coli (bacterium) (1000 nm  3000 nm) Red blood cell (10,000 nm in diameter) Bacterial ribosomes (25 nm) Smallpox virus (200 nm  300 nm) Poliovirus (30 nm) Bacteriophage T4 (50 nm  225 nm) Bacteriophage MS2 (24 nm) Tobacco mosaic virus (15 nm  300 nm) HOW DO VIRUSES ‘PICK’ THEIR TARGETS? HOST RANGE The number of species (usually very few) a virus can infect Viral glycoproteins often key to this process ATTACHMENT OF ANIMAL VIRUSES: 1. DIRECT PENETRATION Capsid Receptors on cytoplasmic membrane Direct penetration Viral genome ATTACHMENT OF ANIMAL VIRUSES: 2. MEMBRANE FUSION Viral glycoproteins Envelope Viral glycoproteins remain in cytoplasmic membrane Receptors on cytoplasmic membrane of host Viral genome Uncoating capsid Membrane fusion ATTACHMENT OF ANIMAL VIRUSES: 3. ENDOCYTOSIS Cytoplasmic membrane of host engulfs virus (endocytosis) Viral genome Uncoating capsid Endocytosis THE ROLE OF THE VIRAL GENOME IN THE HOST CELL Capsomeres Other viral proteins Viral nucleic acid (can be RNA, DNA, single stranded, double stranded) New Viruses Assemble New copies of the viral genome GENOME DIVERSITY DNA or RNA DNA with short segments of RNA DNA or RNA with covalently attached protein + strand, - strand, ambisense, or double stranded Linear or circular Segmented or not Gapped or not CLASSIFYING VIRUSES: BY GENOME TYPE Central Dogma THE BALTIMORE CLASSIFICATION Positive Strand Negative Strand DOUBLE-STRANDED DNA (DSDNA) GAPPED DNA SINGLE-STRANDED DNA (SSDNA) DOUBLE STRANDED RNA (DSRNA) (+) STRAND RNA (+) STRAND RNA WITH DNA INTERMEDIATE Reverse Transcriptase (-) STRAND RNA WHAT DO VIRAL GENOMES LOOK LIKE? THANK YOU! A N D H AV E A L O V E LY D AY !