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

2. 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

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) ~ genes
Accessory structures*
Lipid envelope – from membrane of the host cell
Structure and properties of viruses
TMV
adenovirus
influenza T4

4. 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 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

5. Types of animal viruses

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

10. Virus RNA  mRNA  proteins
RNA virus replication
Virus RNA  mRNA  proteins

11. RNA retrovirus replication Virus RNA  DNA  mRNA proteins
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

13. Bacterial transduction Phage-mediated DNA transfer

14. http://liquidbio. pbworks. com/w/page/11135299/f/SwineEvolution

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