Download 3 rd Step: Replication

• They are not made of
cells or organelles
• They cannot reproduce
without a host
• They do not metabolize
energy
• They do not perform
cellular processes
• Reproduce
• They have DNA or
RNA
• They can adapt to
surroundings
• The have
organization
• Composed of protein coat & nucleic acid
• 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
– Virus acts as a “key”
to the receptor
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
4th Step: Assembly
(formation)
– New virus proteins
are assembled in
the cytoplasm
5th Step: Lyse & Release
– Virus enzyme causes cell membrane to “lyse”
– 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
4th Step: Assembly
Same, except many
new viruses are being
assembled in many
cells
5th Step: Release Same,
except many cells
“lyse” releasing many
more viruses
Retroviruses
• Type of RNA virus that
contains the enzyme
Reverse Transcriptase
• 1) Virus RNA is injected
into cell
• 2) Ribosome uses virus
RNA to create virus DNA
• 3) Virus DNA combines
with cell DNA (becomes
latent)
• 4) Once active, normal
steps of
transcription/translation
followed
How is HIV contracted?
• 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
MSM = men
having sex
with men
IDU =
intravenous
drug users