Download Virus

Virus: A
biological particle composed
of nucleic acid and protein
Intracellular Parasites: organism that
must “live” inside a host
 They
are not made of
cells or organelles
 They cannot reproduce
without a host
 They don’t have both
DNA and RNA
 They do not
metabolize energy
 Reproduce
 They
have DNA
or RNA
 They can adapt
to surroundings
 The have
organization
 All
Have:
• 1) Capsid: coat of
protein that
surrounds DNA or
RNA
• 2) Nucleic Acid: RNA
or DNA
 Some Have:
• Tail Fibers: Used for
attachment (not
legs)
 Shapes vary
 Cannot
reproduce w/o a host cell
• Virulent: cause disease
 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
• Proteins created by
transcription/translat
ion
• Virus proteins make
new virus parts
 4th
Step:
Assembly
(formation)
• New virus parts
are assembled in
the cytoplasm
 5th
Step: Lysis & Release
• Virus enzyme causes cell membrane to
“lyse”
• New viruses are released to find new host
• Cycle repeats
 If
DNA Virus:
• 1) Viral DNA injected
• 2) Viral DNA
transcribed into viral
mRNA
• 3) Viral mRNA
translated into viral
proteins
 If
RNA Virus:
• 1) Viral RNA injected
• 2) Viral mRNA
translated into viral
proteins
 1st
step:
Attachment =
Same
• 2nd Step: Entry =
Same
 3rd
step:
Replication
• Virus DNA
combines with
cell DNA, and
waits…
• Cell divides as
usual
• Each new cell will
have virus DNA
inside
 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
 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