Virus Basics. General Characteristics of Viruses 5/9/2011. General Characteristics of Viruses. Chapter 13 & 14. Non-living entities

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1 Virus Basics Chapter 13 & 14 General Characteristics of Viruses Non-living entities Not considered organisms Can infect organisms of every domain All life-formsf Commonly referred to by organism they infect General Characteristics of Viruses 1

2 General Characteristics of Viruses Virus architecture Consists of nucleic acid surrounded by protein coat Viruses have different shapes Isometric Helical Complex Two types of virion Naked without envelope Enveloped surrounded by lipid membrane General Characteristics of Viruses Viral genome Contains only single type of nucleic acid Either DNA or RNA NEVER BOTH Can be linear or circular Single-stranded or doublestranded Replication cycle overview Only multiply inside metabolizing cell Use host machinery to support reproduction Every virus contains information to make viral proteins, assure replication and move in and out of host cells Viruses live in two phases Extracellular phase Metabolically inert Intracellular phase Metabolically active Why does a virus need a host cell? Viral particle (virion) Host cell Release of many viral particles 2

3 Why does a virus need a host cell? Viral particle (virion) Host cell Release of many viral particles In general, enveloped viruses are more susceptible to drying and disinfectants Viruses that Infect Bacterial Cells: Bacteriophage Infections Infection Process (productive) Attachment - via specific receptors on host; lack of receptor resistance 3

4 Infection Process (productive) Penetration - genome is injected into cell Infection Process (productive) Transcription/translation early proteins - ex. nucleases Infection Process (productive) Replication of phage Replication of phage genome Transcription/translation late proteins - capsid proteins 4

5 Infection Process (productive) Assembly - self-assembly Infection Process (productive) Release - often lysis, sometimes extrusion (lytic phages lyse hosts) Burst size Infection Process (productive) 5

6 What is the Difference Between a Productive and Latent Infection? Viral particle (virion) Host cell What is the Difference Between a Productive and Latent Infection? Viral particle (virion) Host cell What is the Difference Between a Productive and Latent Infection? Viral particle (virion) Host cell 6

7 Virus Interactions with Host Cells Lysogeny Replication of a temperate virus This is a non-productive cycle Lysogeny begins like the lytic cycle Adsorption Penetration, then; Incorporation Latent infections Temperate phage Two options: 1) Lytic cycle 2) Lysogenic cycle Latent infections Temperate phage Two options: 1) Lytic cycle 2) Lysogenic cycle 7

8 Latent infections Temperate phage Two options: 1) Lytic cycle 2) Lysogenic cycle Integration/replication Phage senses stresslevel of the host cell repressor Latent infections Immunity of lysogens Lysogenic conversion repressor 8

9 Latent infections Immunity of lysogens repressor Lysogenic conversion Viruses that Infect Animal Cells Viral particle (virion) Host cell Release of many viral particles Infection Process Attachment Penetration fusion with the host membrane (enveloped viruses only) 9

10 Infection Process Attachment Penetration fusion with the host membrane (enveloped viruses only) receptor-mediated endocytosis Replication genome protein synthesis Assembly Release Cell death lysis Budding Infection Process Attachment Penetration fusion with the host membrane (enveloped viruses only) receptor-mediated endocytosis Replication genome protein synthesis Assembly Release Cell death lysis Budding acquisition of envelope Acute Infections 10

11 Persistent Infections shingles Key feature in viral classification QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. ATGCC TACGG Key feature in viral classification ds DNA ss DNA 11

12 ATGCC TACGG initial template DNA polymerase final product ds DNA ss DNA ATGCC TACGG ATGCC initial template DNA polymerase final product ds DNA ss DNA AUGCC UACGG ds RNA ss RNA 12

13 AUGCC UACGG RNA-dependent RNA polymerase Virally-encoded initial template enzyme (replicase) final product ds RNA ss RNA (+) strand (mrna) (-) strand (-) ss RNA viruses must bring own replicase made during prev. infec. AUGCC UACGG RNA-dependent RNA polymerase Virally-encoded initial template enzyme (replicase) final product ds RNA ss RNA (+) strand (mrna) (-) strand 5 3 (-) ss RNA viruses must bring own replicase made during prev. infec. Long ds RNA signifies to our cells that they are virally-infected AUGCC UACGG RNA-dependent RNA polymerase Virally-encoded initial template enzyme (replicase) final product ds RNA ss RNA (+) strand (mrna) (-) strand (-) ss RNA viruses must bring own replicase made during prev. infec. ^and ds RNA viruses 13

14 Retroviruses: ss (+) RNA ds DNA ss (+) RNA Reverse transcriptase DNA copy integrates into the host cell s genome Retroviruses: ss (+) RNA ds DNA ss (+) RNA * * Reverse transcriptase DNA copy integrates into the host cell s genome * Virally-encoded enzymes Target for antiviral drugs ex. AZT - nucleotide analog Error-prone ( mutations) Growing Bacteriophage in the Laboratory Lawn of host cells Plaques 14

15 Growing Eukaryotic Viruses in the Laboratory Tissue culture Growing Eukaryotic Viruses in the Laboratory Tissue culture 15