Virus - Latin name for poison

Characteristics

• Does not fit in the 6 kingdom classification system

• A chemical that carries out no life function of its own

• Invades a living/host cell; displays a trait that is shared with all living things: Reproduction

Cont’d

• 20-400 nm (nanometre=1 billionth of a metre)

• Less complex than simple organisms

• Nucleic acid core contains only DNA OR RNA.– Not both, unlike other living organisms

• Bacteriophages are a category of viruses that infect bacteria (eaters of bacteria)

– Outer protective protein coat (Capsid)– Inner nucleic acid core

Viral Diversity

• Viruses must enter cells to carry out life processes– not all are considered disease causing agents or

pathogens • Selective to specific host cells• First viruses discovered infected higher plants

and animals• Bacteriophages were discovered in 1940– they have been the main experimental subject for

examining biological properties of viruses

Viral Specificity

• Highly specialized relationship with host– Only plants OR animals OR bacteria

• Host Range: the limited number of host species or cells that a virus or parasite can infect

• Bacteria – restricted host range• Animals – broad host range• Plants – very wide host range

Viral Replication• Replication: process where genetic material is duplicated

before the cell divides1) Attachment: recognizes a host cell and attaches to it2)Synthesis: of protein and nucleic acid. Molecular

information in the DNA/RNA directs host cell in replicating components of the virus

3) Assembly: viral components are put together, making new virus particles

4) Release: new virus particles are released and the host cell dies

^^^^^^^^^^LYTIC CYCLE^^^^^^^^^

Cont’d

• 25-45 minutes results in 300 new virus particles• Lysogenic cycle:– does not kill the host cell– nucleic acid is injected into DNA/RNA of host cell– replicated with the host cell’s DNA acting as another

set of genes on the host chromosome– DNA is then passed along to daughter cells

• In a dormant state, until it is activated by a stimulus and the cycle becomes lytic again (ex. Cancer-causing virus)

Human Health

• As the virus reproduces it attacks the host cell, this damage to the cells is what causes the symptoms of a disease

• Vaccination: solutions that are prepared from viral components or inactivated viruses

• As if the body was infected with the real virus – produces antibodies– antibodies stay with us– we are then immune to that

specific disease

Any Question?

Activity

• Draw a picture of your own made up virus. Be creative!– Include a description of what its host is and what

kind of effect it has on it– Label the outer protective protein coat (Capsid)

and the inner nucleic acid core

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