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What is a Virus?
• Virus: A biological particle composed of
nucleic acid and protein
• Intracellular Parasites: organism that must
“live” inside a host
• Not made of cells or
organelles
• Can’t reproduce on own
• Don’t metabolize energy
• Don’t perform cellular
processes
• Reproduce
• Have nucleic acid
• Adapt to
surroundings
• Have organization
• All Have:
– 1) Capsid: coat of
protein that surrounds
nucleic acid
– 2) Nucleic Acid: RNA
or DNA
• Some Have:
– Tail Fibers: Used for
attachment (not legs)
• Shapes vary
Virus Video
• Bacteriophages (infect bacteria) are often studied
– Replication is similar with many animal
viruses
1st Step: Attachment
– Virus lands on cell
membrane
– Virus attaches to a
cell receptor
– No attachment = No
infection
» Lock & key
analogy
endocytosis
2nd Step: Entry
– Virus enzyme weakens cell membrane
– Genetic material (DNA or RNA) enters host cell
3rd Step: Replication
– Virus DNA/RNA uses
ribosomes to make
virus proteins
– Virus proteins created
by transcription/
translation
Viral DNA  Viral RNA  Viral Amino Acids  Viral Proteins
4th Step: Assembly
– New virus proteins
are assembled in
the cytoplasm
5th Step: Release
– Virus enzyme causes cell membrane lyse (burst)
– Viruses are released to find new host
– Cycle repeats
1st step: Attachment =
Same
2nd Step: Entry =
Same
3rd step: Replication
– Virus DNA
combines with cell
DNA, and waits
• Provirus = cell DNA +
viral DNA
– Cell divides by
mitosis
– Each new cell will
contain the provirus
Host
Procell
virus
DNA
Provirus
Provirus
Provirus
Provirus
Provirus
4th Step: Assembly
Same, except many
new viruses are being
assembled in many
cells
5th Step: Release
Same, except many
cells burst releasing
many more viruses
The viral DNA become active and starts making new viral proteins
The infected cells burst…releasing the new viruses
Retroviruses
• RNA viruses
• Contains the enzyme
Reverse Transcriptase
• Steps
– 1) Virus RNA enters host
cell.
– 2) Reverse transcription
takes place to make virus
DNA
– 3) Virus DNA combines
with cell DNA (provirus
created)
– 4) Once active, normal steps
of transcription/translation
followed.
How is HIV contracted?
High Risk Activities
Low Risk Activities
• High risk activities: • Low risk activities:
– 1) Sex (oral, vaginal,
anal)
– 2) Sharing needles
(tattoos, piercings, drugs)
– 3) Mother to child in womb
– 4) Breast milk
– 5) Blood transfusions
Adults and children estimated to be living
with HIV/AIDS as of end 2001
North America
940 000
Caribbean
420 000
Latin America
1.4
million
Eastern Europe
& Central Asia
Western Europe
560 000 1 million
North Africa
& MiddleEast
440 000
Sub-Saharan
Africa
East Asia & Pacific
1 million
South
& South-East Asia
6.1 million
28.1
million
Total: 40 million
Australia
& New
Zealand
15 000
What is AIDS?
New
Exposures to
HIV (2006)
Gender of those living
with HIV (2003)
• Acquired Immunodeficiency Syndrome
• AIDS results when:
– 1) Amount of T-cells drop (200 T-cells per 1mm³ blood)
– 2) Multiple symptoms/infections appear
• Rash, fever, headache, sore throat, swollen lymph nodes
• Therefore, the HIV virus causes the disease AIDS by killing
your T-cells
Female Transmission of HIV
(2006)
Male Transmission of HIV
(2006)
Want more stats? Go to the Centers for Disease Control’s Website
http://www.cdc.gov/hiv/topics/surveillance/united_states.htm