Viruses Living a borrowed life Discovery Structure and properties Types of viruses Significance Origin of viruses Viral reproductive cycles Viruses Living a borrowed life

Discovery of the tobacco mosaic virus Tobacco mosaic disease could be transferred between plants Adolf Mayer (1886) Pathogen is non-bacterial and can pass through fine filters Dmitri Ivanovsky (1892) Independently replicated Ivanovsky’s experiments Agent was able to reproduce and multiply in host cells of tobacco plants Coined term “virus” Martinus Beijerinck (1898) Discovery of the tobacco mosaic virus

Structure and properties of viruses Small infectious agent that can only replicate inside the living cell of an organism Virus particles (virions) Protein coat/capsid formed from capsomeres Nucleic acid core (DNA/RNA) ~ 4-1000 genes Accessory structures* Lipid envelope – from membrane of the host cell Structure and properties of viruses TMV adenovirus influenza T4

Virus classification Genetic material Shape Size Presence of envelope DNA (dsDNA, ssDNA) RNA (dsRNA, ssRNA) Linear/circular in form Shape Helical Icosahedral Enveloped viruses Complex Size Usually 17-300 nm Some can reach up to 14µm Presence of envelope Usually present in animal viruses Host specificity Due to specific attachment sites in hosts called receptors May infect bacteria, archaea, protists, algae, plants, fungi, animals Type of reproductive cycle Lytic cycle Lysogenic cycle Retroviruses (RNA viruses) Virus classification http://3.bp.blogspot.com/_QUryhHJZKbU/S8uRMF8FD3I/AAAAAAAACI0/CINIMHP5Cmc/s320/Rhinotracheitis+Capsid.jpg

Types of animal viruses

Virus reproductive cycles Enveloped Virus

LYTIC vs lysogenic cycles in dsdna bacteriophages/Animal viruses

examples LYTIC VIRUSES influenza rhinovirus (common cold) LYSOGENIC VIRUSES herpes I and II some retroviruses MIXED STAGE VIRUSES http://www.slic2.wsu.edu:82/hurlbert/micro101/images/vir5.gif

Virus RNA  mRNA  proteins RNA virus replication Virus RNA  mRNA  proteins

RNA retrovirus replication Virus RNA  DNA  mRNA proteins http://www.web-books.com/eLibrary/Books/B0/B22/MAIN/images/HIVcycle.gif RNA retrovirus replication Virus RNA  DNA  mRNA proteins

HYpotheses on viral origins Progressive theory Genetic material from cells escaped and mutated Regressive theory Evolved from bacteria that are obligate intracellular parasites Virus-First Hypothesis Evolved from the first RNA segments before the early cells Viroids – RNA sequences that infect plants http://blogs.sciencemag.org/origins/WindowsLiveWriter/bc47e94c78c7_9B1A/mutation-v-genome_3.jpg

Bacterial transduction Phage-mediated DNA transfer http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap9.html

http://liquidbio. pbworks. com/w/page/11135299/f/SwineEvolution http://liquidbio.pbworks.com/w/page/11135299/f/SwineEvolution.png, http://i2.squidoocdn.com/resize/squidoo_images/590/draft_lens4362032module30604592photo_1241127545geentic_makeup_of_flu.jpg

SIGNIFICANCE OF VIRUSES pathogens viral gene therapy phage typing of bacteria source of enzymes pesticides antibacterial and anticancer agents molecular biology breakthroughs genetics and evolution http://en.wikipedia.org/wiki/File:LambdaPlaques.jpg