Download Virus - Belle Vernon Area School District

Virus Drill 1
1.
What are the two essential components of
a virus?
2.
How do viroids & prions compare to
viruses?
3.
Name three differences between viruses &
cells.
Virus Drill 2
1. List the stages of the lytic cycle.
2. Describe the structure of the
bacteriophage.
3. Define a prophage.
4. How do scientist’s believe the first viruses
evolved?
Virus Drill 3

1. Explain why viruses are non living.

2. Define the following…
–
–
–
–
Capsid
Spikes
Enveloped
Naked
3. What are the 3 common shapes of viruses?
Virus Drill 4
1.
What are the three ways a virus can
interact with the host cell?
2. What does lytic mean?
3. What are the stages of the lytic life cycle?
Name a virus that uses the lytic cycle?
Drill 5

Define a virus.

What are the outer of virus called?

Explain why viruses are non living.
Drill 6

Define and give an example of a zoonotic
disease.

How is a persistent disease different from an
acute disease? Give examples of each.

What is meant by a latent virus? Give an
example of it.

How are chronic viruses different from slow
infections? Give an example of each.
Virus 7
1.
Describe the lytic life
cycle.
2.
Describe the lysogenic life
cycle.
Virus 8
1. What is the difference between active &
passive immunity?
2. Why are antibiotics not effective against
viruses?
3. What is a vaccine & how is it useful?
Virus
Viruses
I. General Characteristics
A. Non- living agents
Lacking energy - ATP
Lacking organelles (Ribosomes)
Has DNA or RNA, but not both
Can only grow within living cells
Has 2 phases in their life cycle
Outside - dead - metabolically inert - only considered a
macromolecule.
Inside - living- uses host machinery to produce virons (Viruses).
II. Size
Variety of shapes but size is well below the limit of visibility
in a light microscope.
100 - 1,000 X’s smaller than the cells they infect (20 - 250
nm).
III Shapes & Design
A. Polyhedral
B. Helical
C. Combination
D. Enveloped -lipid layer acquired from the infected cell’s
membrane during the release of the virus or Naked.
E. Capsid - protein coat for protection
F. Nucleic Acids
1. DNA - double (rare) or single stranded - contains all
the genetic information in a singular linear
molecule.
2. RNA - double (rare) or single.
G. Capsomere - Identical protein sub-units.
H. Nucleocapsid - viral capsid with it’s nucleic acid.
I. Spikes - Attachment proteins.
IV. Viral & Host’s Interactions
A. Little is understood between viruses & animal cell’s
because of the complexity of the animal cell.
10,000 X Bigger DNA
1,000 X bigger
100 X longer to divide
B. Viruses can have different relationships to their host cell.
May kill it.
May become apart of the hosts genome
Modify properties of the cell.
V. Life Cycles
A. Virulent or Lytic Life cycle - Host cell always dies.
DNA Virus
1. Attachment - Virus attaches to host cell at receptors.
2. Entry - Viral N.A. enters the cell.
(Lysozymes enzymes degrade the bacterial cell wall &
DNA is injected into the cell.
3. Replication
a. Phage -induced proteins - First enzymes to be
produced by the viral DNA.
Nuclease - degrades the host’s cell’s DNA
(early).
Enzymes that lyses the bacteria’s cell wall
(late).
b. Vegetative Replication - New viral components are
produced.
4. Assembly (maturation) - Viral components self asemby
(no enzymes are needed).
5. Release
a. Enzymes degrade the bacteria’s cell wall (weak).
b. Viruses burst out of the cell which kills it.
c. Releases up to 200 new viruses.
Review

What are the stages of the lytic cycle?

What are the three basic shapes of a
virus?
B. Temperate or Lysogenic - DNA becomes integrated into the host’s genetic
material
Prophage or Provirus - Viral DNA that has been incorporated into the host
cell.
Lysogenic or lysogen - Bacterial cell carrying the prophage.
1. Attachment - Virus attaches to host cell at receptors.
2. Entry - Viral N.A. enters the cell & is integrated into the host cells
DNA.
(Lysozymes enzymes degrade the bacterial cell wall & DNA
is injected into the cell.
3. Repressed or Dormant.
Repressor must function continuously.
Could last indefinitely.
Lysogenic cell is immune to further infections from
the same virus but not different ones.
Lysogenic conversion - Prophage gives the cell new
properities.
Corynebacterium diphtheriae - diptheria
Streptoccus pyogenes - scarlet fever
Clostridium botulinum - botulism
4. Induction to lytic cycle.
Propahge becomes active for any reason.
Activation of the SOS repair which destroys the repressor.
Review

What are the stages of the lysogenic
cycle?

Can the lysogenic cycle stay dormant
forever? What can trigger the lysogenic
cycle to go lytic?
C. Filamentous Phages
Extrusion - Constantly releases new viruses without
being destroyed.
Carrier cells - infected cells.
1. Long & thin
2. Infect only E. coli (F+).
3. Do not completely take over the host cells
metabolism.
4. Can not be detected in the cytoplasm of the host
cell, maybe stored in the cell’s membrane.
D. Transduction
Bacterial DNA is transferred from one bacteria to another by either
replacing or tagging along with viral DNA.
1. Generalized Transduction - replaces viral DNA
Both Virulent & Temperate life cycles.
Pieces of bacterial DNA fragments are placed into the capsid
instead of viral.
Transferred to another bacteria & integrated In the new
bacteria’s DNA.
Does not kill the bacteria because the viral genetic information
to do that is missing or replaced by bacterial DNA - known as a
defective phage.
2. Specialized Transduction - tags along with viral DNA
Only temperate viruses can carry them.
Review

How is a filamentous virus different from
lytic and lysogenic?

Define transduction.

How is generalized different from
specialized?
VI. Host Range of Viruses
Viruses can only infect a certain range of cells - Host range.
ex. Bacteria, fungi, algae, pants, & animals
Some are specific T4 - only with bacteria, Polio - only with
humans
Some may be wider – rabies
Determine by the presence of absence of receptors on the
host cell needed by the virus to attach.
VII Animal Viruses
A. Classification
 1. Nucleic Acids - single of double stranded DNA or RNA.
2. Capsid shape.
3. Presence or absence of an envelope.
4. Size.
5. Route of transmission.
 a. Enteric viruses - ingested on material
contaminated by feces.
 b. Respiratory viruses.
 c. Zoonosis - animal to human.
 d. Sexually transmitted viruses.
 6. Strategy of viral replication.




B. Interaction of Animal Viruses with their Hosts.
 1. Acute
.Fast acting
.Remains localized
.Mumps, measles, flu
2. Persistent Infections - always present in the body. Late
Complications - Subacute sclerosing panencephalitis (SSPE)
.Follows measles
.10 years after infection
.1 in 300,000
.Onset, few viruses in brain.
.Nerve cells prevent viral replication.
b. Latent Infections - Infectious particles cannot be detected
until reactivation of the disease.
1. Herpes (HSV-1, HSV-2)
Initial infection is acute, may not lead to ay
symptoms.
Infects sensory nerve cells where it remains
non-infectious.
Replication of viruses remains suppressed.
Activated by stress - fever, sunburn.
Infectious viruses are produced & carried to the
skin = cold sore.
Cold sores heal, virus is dormant again.
2. Chicken Pox (varicella- another member of the
herpes family).
Initial infection - rash
Remains latent for years
Reactivated - shingles (herpes zoster).
c. Chronic Infections - demonstrated all the time.
Hepatis B (serum hepatitis)
Carrier state - can be detected in body fluids.
Plasmid state - integrated into the liver cells
d. Slow Infections - Infection gradually increases over
time.
1. AIDS
e. Prions - Self replicating protein the causes
diseases in humans.
neurological
C. Oncogenic Viruses - RNA - causes cancer
1. Retro viruses - group of RNA viruses that produces cancer
Nondefective - replicates independently within the host cell.
Rapid transformation
Defective - requires a helper virus - malignancies
VIII. Plant Viruses - Majority are ssRNA (+) or (-)
A. Economic importance, a serious infection may reduce
crop yield by 50%.
B. Localized abnormalities.
Discoloration due to the destruction of chlorophyll
Tumors
Deformed structures
Sometime it’s desired - colors in tulips
C. Transmission
1. Infection due to injury to part of the plant which
permits the virus
to enter.
2. Contaminated soil from other infected plants.
3. Insect, worms, fungi, human handling.
a. Temporary transmission - virus is associated
around the mouth parts of the vector.
b. Circulative transmission - virus circulates but
does not replicate in the insects body.
c. Replication of virus in the insect, infects both
insect & plant.
Aphid & Leaf hoppers
D. Viroid
1. Unprotected ssRNA found ONLY in plants.
2. 1/10 the size of the smallest known RNA virus.
E. Satellite Viruses
1. Can only replicate if a HELPER Virus is present with in the
same infect cell.
Review

How many crops are affected by viruses each
year?

How can viruses that infect plants be spread?

What is a viroid? How is it different from
prions?

How is a satellite virus different from a regular
virus?