PAP Biology Virus Cornell Notes
Answer guided
question here.
Answer guided
question here.
Answer guided
question here.
Explain why a virus is considered to be non-living.
 Viruses - Biological particles that are NOT made of
cells.
– Viral particles are extremely small in size.
– Don’t eat, respire or respond to their
environment. (No metabolism.)
– Parasitic: they require a host.
 Host is an organism that shelters and
nourishes something.
– Host provides the virus with all the materials
needed to make copies of itself can NOT
reproduce on its own.
– Therefore, viruses are considered to be nonliving.
Describe the Structure of a Virus.
 Capsid: protective coat made of protein
 DNA orRNA: nucleic acids
– Influenza virus has DNA
– Retrovirus has RNA
 Envelope: outer lipid layer and an inner protein layer
surrounding the capsid
 Projections: spike projections on the envelope that
helps recognize and attach to a host cell
What makes a retrovirus different from all other
organisms we study?
 A retrovirus is a virus that contains an RNA core as
it’s genetic material that replicates by transcribing it’s
RNA into DNA. The DNA is then incorporated into
the host’s genome.
– Retro means reverse order or backwards.
– Retroviruses have an enzyme called reverse
transcriptase which makes RNA transcribe
DNA.
PAP Biology Virus Cornell Notes
Draw 4 virus shapes:
Answer guided
question here.
Answer guided
question here.
 Shape (draw each in column to left)
– Polyhedral virus: geometric shapes (colds)
–
Binal virus: 2 parts – polyhedral capsid and
helical tail
–
Helical virus: helical with nucleic acid coil
(influenza)
–
Filovirus: threadlike or looped at the end (Ebola)
Compare and contrast how viruses reproduce.
 Lytic cycle ex. Chicken pox (Page 481)
– rapid cycle
– 1 Virus invades the cell by attaching and
injecting it’s genetic material
– replication occurs with genetic material
incorporated into host’s genome.
– many new viruses are made
– cell lyses (dies/breaks apart)
– many viruses are released to invade new cells
 Lysenogenic cycle ex. Cold sores
– delayed symptoms
– Does NOT kill cell immediately
– Viral DNA segment attaches to the cell’s
chromosome prophage
– Some prophage remains in the lysogenic cycle
indefinitely
– Environmental stimulus causes the prophage to
separate into lytic cycle
How are viral diseases different from those caused by
other factors?
Viruses are pathenogenic meaning they cause disease.
 Diseases caused by viruses:
– animal viruses (rabies, feline leukemia, mad cow)
PAP Biology Virus Cornell Notes
plant viruses (tobacco mosaic, turnip yellow
mosaic)
– bacterial viruses - bacteriophage is a virus that
infects bacterial cells.
– Can also cause disease in humans (flu, measles,
HIV, herpes, warts)
–
Viral diseases can NOT be treated using antibiotics. They
must run their course or be prevented by vaccination.
VIRUS
SUMMARY: