VIRUSES

LIVING A BORROWED LIFE

DISCOVERY OF THE TOBACCO MOSAIC

VIRUS

• 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 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

RNA virus replicationVirus RNA mRNA proteins

RNA retrovirus replicationVirus RNA DNA mRNA proteins

http://www.web-books.com/eLibrary/Books/B0/B22/MAIN/images/HIVcycle.gif

• 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

HYPOTHESES ON VIRAL ORIGINS

http://blogs.sciencemag.org/origins/WindowsLiveWriter/bc47e94c78c7_9B1A/mutation-v-genome_3.jpg

Viroids – RNA sequences that infect plants

BACTERIAL TRANSDUCTIONPhage-mediated DNA transfer

http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap9.html

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

• pathogens

• viral gene therapy

• phage typing of bacteria

• source of enzymes

• pesticides

• antibacterial and anticancer agents

• molecular biology breakthroughs

• genetics and evolution

SIGNIFICANCE OF VIRUSES

http://en.wikipedia.org/wiki/File:LambdaPlaques.jpg