1. To be considered living…
An organism must meet ALL 5 criteria:
Be made of cell(s); cells are the smallest living units
Metabolize nutrients for energy
Reproduce
Have a genetic blueprint
Maintain homeostasis

2. Cells are the smallest living units
They can live as individual entities, or work together to form multi-cellular organisms. 
Simple Complex
cell
tissue
organ
organ system
organism

3. Cells are the smallest living units
Cells convert nutrients to useable energy
Cells reproduce
Cells have DNA
Cells move, grow, respond to their surroundings, and exchange substances with their environment. 
Because of these characteristics, cells are classified as LIVING. 

4. Cells are classified as either…
Prokaryotes
Eukaryotes
Examples
Eubacteria, Archaebacteria
Plants, Animals, Protists, Fungi
Size
~1 µm µm
Organelles
No membrane bound organelles like a nucleus, but they do have ribosomes
YES! Membrane bound organelles
Genetic Material
DNA is in a circular shape
DNA is in chromosomes
Reproduction
Binary fission or conjugation
Mitosis or meiosis

5. Are Viruses Alive?
Viruses are particles containing DNA or RNA surrounded by a protein coat called a capsid. 
They do not contain cytoplasm, respire, or grow, and they cannot replicate without a host cell.
Because of these characteristics, scientists DO NOT consider viruses as living.

6. Viruses vs. Cells Viruses Prokaryotes Eukaryotes Examples
Influenza, HIV
Eubacteria, Archaebacteria
Plants, Animals, Protists, Fungi
Size nm
~1 µm µm
Organelles
None
No membrane bound organelles like a nucleus, but they do have ribosomes
YES! Membrane bound organelles
Genetic Material
DNA or RNA
DNA is in a circular shape
DNA is in chromosomes
Reproduce
MUST hijack host cell to reproduce
Binary fission or conjugation
Mitosis or meiosis

7. Viral Structure Basic structure:
Capsid: a protein coat which contains either RNA or DNA inside.
Nucleic acid core: contains either RNA or DNA.
Possible additional features:
Envelope: surrounds the capsid.
Helps virus enter cells.
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8. Viral Shapes Helical viruses (Tobacco Mosaic Virus)
Polyhedral viruses – many sides (Adenovirus)
Spherical viruses (Influenza)
Complex viruses (Bacteriophage)
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9. Virus Reproduction Viruses replicate in either the
LYTIC cycle - immediate replication of nucleic acids and lysis of host cell. or
LYSOGENIC cycle - delayed replication after latent (dormant) period including integration into host chromosome.

10. LYSOGENIC CYCLE Virus ATTACHES to host cell
Virus INSERTS DNA into host cell, which incorporates it into its own DNA
The inserted DNA (prophage) remains dormant until it is activated 
Once activated, it separates from the host cell's DNA and enters the lytic cycle

11. LYTIC CYCLE Virus ATTACHES to host cell
Virus INSERTS DNA into host cell
Host cell REPLICATES the viral DNA, thousands of new viruses are assembles
Host cell bursts to RELEASE the viruses into the body

12. HIV (human immunodeficiency virus)
HIV is a lysogenic virus. 
When the virus enters the lytic cycle, it causes AIDS (acquired immune deficiency syndrome). 
HIV targets white blood cells of the immune system, and AIDS destroys them. 
HIV is a retrovirus that transcribes DNA from RNA.

13. Influenza (flu)
Influenza (flu) virus is a lytic virus. It reproduces and affects the host quickly. 
The immune system is capable of destroying it, provided there are no other health complications. 
H1N1 is a type of flu virus that is highly contageous.

14. Viral Treatment Viruses must run their course.
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Viruses must run their course.
Only the symptoms of a disease caused by a virus can be treated.
Antibiotics do not treat viruses!
Vaccines: a substance prepared from killed or weakened pathogens and introduced into a body to produce immunity. It can only protect the body against future infections.
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