Viruses Living a borrowed life

1
VirusesLiving a borrowed life
2
Discovery of the tobacco mosaic virus
3
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

TMV
adenovirus
influenza
T4
4
Virus classification
http//3.bp.blogspot.com/_QUryhHJZKbU/S8uRMF8FD3I/
AAAAAAAACI0/CINIMHP5Cmc/s320/RhinotracheitisCapsi
d.jpg
5
Types of animal viruses
6
(No Transcript)
7
Virus reproductive cycles
Enveloped Virus
8
LYTIC vs lysogenic cycles in dsdna
bacteriophages/Animal viruses
9
examples

• LYTIC VIRUSES
• influenza
• rhinovirus (common cold)
• LYSOGENIC VIRUSES
• herpes I and II
• some retroviruses
• MIXED STAGE VIRUSES

http//www.slic2.wsu.edu82/hurlbert/micro101/imag
es/vir5.gif
10
RNA virus replication Virus RNA ? mRNA ? proteins
11
http//www.web-books.com/eLibrary/Books/B0/B22/MAI
N/images/HIVcycle.gif
RNA retrovirus replication Virus RNA ? DNA ?
mRNA? proteins
12
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/WindowsLiveWri
ter/bc47e94c78c7_9B1A/mutation-v-genome_3.jpg
13
Bacterial transductionPhage-mediated DNA transfer
http//www.slic2.wsu.edu82/hurlbert/micro101/page
s/Chap9.html
14
http//liquidbio.pbworks.com/w/page/11135299/f/Swi
neEvolution.png, http//i2.squidoocdn.com/resize/s
quidoo_images/590/draft_lens4362032module30604592p
hoto_1241127545geentic_makeup_of_flu.jpg
15
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/FileLambdaPlaques.jp
g