Virology

Virology

Tuesday, January 26, 2010

Virus


Virus ✴Particle made of
nucleic acid and a
protein coat


nucleic acid and a
protein coat
✴~100x smaller than
our cells


nucleic acid and a
protein coat
✴~100x smaller than
our cells
✴Virology-the study of
viruses (structure,
classification, isolation,
potential uses)

The Great Debate


The Great Debate
✴Are viruses living organisms?


You Be the Judge


You Be the Judge
✴They have nucleic acids (DNA or RNA)


You Be the Judge
✴No membrane bound organelles


You Be the Judge
✴They cannot metabolize or divide


You Be the Judge
✴They cannot metabolize or divide
✴Must use a host to reproduce


Structure


Structure
✴Nucleic acid surrounded by a capsid
coat


Structure
coat
✴4 types:


Structure
coat
✴4 types:
✴helical


Structure
coat
✴4 types:
✴helical
✴icosahedral


Structure
coat
✴4 types:
✴helical
✴icosahedral
✴enveloped


Structure
coat
✴4 types:
✴helical
✴icosahedral
✴enveloped
✴bacteriophage

Helical Virus


Helical Virus
✴Spiral tube of protein (“stair case”)


Helical Virus
✴Spiral tube of protein (“stair case”)
✴Tobacco mosaic virus, rabies


Icosahedral Virus


Icosahedral Virus
✴Appear spherical at low mag.


Icosahedral Virus
✴They actually have 20 triangular sides


Icosahedral Virus
✴They actually have 20 triangular sides
✴Hepatitis B


Enveloped Virus


Enveloped Virus
✴Spherical shape


Enveloped Virus
✴Spherical shape
✴These viruses highjack a host’s cell
membrane, forming an envelope


Enveloped Virus
✴Spherical shape
✴Glycoproteins (“receptors”) on the surface
of the envelope allow the virus to appear
“friendly”


Enveloped Virus
✴Spherical shape
✴Glycoproteins (“receptors”) on the surface
of the envelope allow the virus to appear
“friendly”
✴HIV, influenza


Bacteriophage
“Complex Viruses”


Bacteriophage
✴Hexagonal head bound to a helical tail


Bacteriophage
✴Resemble a lunar landing pod


Bacteriophage
✴Tail fibers act (“legs”) help to inject DNA
into the host cell


Bacteriophage
✴Tail fibers act (“legs”) help to inject DNA
into the host cell
✴T Phages (E.coli)


Bacteriophage


Bacteriophage
Replication


Bacteriophage
Replication
✴Lytic Cycle- during the lytic cycle a
virus invades a host, produces new
viruses, and destroys the host (lysis)


Bacteriophage
Replication
✴Viruses that replicate this way are
known as virulent


Bacteriophage
Replication
✴Viruses that replicate this way are
known as virulent
✴T phages are virulent

Bacteriophage
Replication
wLysogenic Cycle- sometimes a virus may
infect a host cell and remain dormant


Bacteriophage
Replication
wThis type of virus is known as a
temperate virus


Bacteriophage
Replication
wThis type of virus is known as a
temperate virus
wTemperate virus DNA will combine with
host DNA creating a prophage

Viral Replication


Viral Replication
✴Infection begins when a virus recognizes
and attaches to or enters a host cell


Viral Replication
✴The viral genome takes over the cell,
making it a factory for more viruses


Viral Replication
✴The viral genome takes over the cell,
making it a factory for more viruses
✴Because they can only replicate with the
help of a host, viruses are known as
obligate intracellular parasites


✴DNA Viruses:


✴DNA Viruses:
✴Some DNA enters a host and makes mRNA


✴DNA Viruses:
✴Other DNA may actually insert into a host
cell’s chromosome (provirus)


✴DNA Viruses:
✴RNA Viruses:


✴DNA Viruses:
✴RNA Viruses:
✴Some RNA enters the host and serves
directly as RNA


✴DNA Viruses:
✴RNA Viruses:
✴Some RNA enters the host and serves
directly as RNA
✴Other RNA may be transcribed and serve
as a template for more viral DNA

✴Some RNA viruses (retroviruses) contain
the enzyme reverse transcriptase


✴This enzyme is used to transcribe viral
RNA into DNA (reversing the normal
process of transcription)


✴This viral DNA is used to make more
viruses


✴This viral DNA is used to make more
viruses
✴HIV is a retrovirus


Virology
Part Deux


Human Viral Diseases


Human Viral Diseases
✴Because viruses aren’t “alive” they must
be spread by an intermediate host
(vector)


Chicken Pox/Shingles:


✴Caused by vericella-zoster herpesvirus


✴Spread through the air and contact


✴Spread through the air and contact
✴May remain dormant as a provirus and
become shingles


Viral Hepatitis


Viral Hepatitis
✴Inﬂammation of the liver caused
by 5 different viruses


Viral Hepatitis
✴A and E spread by fecal matter


Viral Hepatitis
✴A and E spread by fecal matter
✴B,C and D spread by sexual
contact or blood transfusion


AIDS


AIDS
✴Acquired Immune Deficiency Syndrome


AIDS
✴Caused by the HIV virus


AIDS
✴Glycoproteins on the surface of the virus
bind to receptor sites of immune cells
(macrophages)


AIDS
(macrophages)
✴Retrovirus, Provirus


AIDS
(macrophages)
✴Retrovirus, Provirus
✴Genetically diverse


Is there a cure ?


Is there a cure ?
✴Azydothymidine- inhibits reverse
transcriptase


Is there a cure ?
transcriptase
✴Protease inibitors- blocks synthesis of
new capsids


Is there a cure ?
transcriptase
✴Protease inibitors- blocks synthesis of
new capsids
✴These drugs can only slow the
progression to full-blown AIDS


Emerging Diseases


Emerging Diseases
✴Caused by infections in animal
populations


Emerging Diseases
populations
✴Rainforest animals-> Ebola


Emerging Diseases
populations
✴Hanta virus (pneumonia)-> mice


Emerging Diseases
populations
✴Hanta virus (pneumonia)-> mice
✴SARS-> civet cats


✴Epidemic- quickly spreading infectious
disease


disease
✴Pandemic- disease spreads over large
regions


disease
✴Pandemic- disease spreads over large
regions
✴Bubonic plague, Small pox


Treatment


Treatment
✴Vaccine- harmless version of a virus used to
build an immune response (microevolution)


Treatment
✴Inactivated virus- not able to replicate


Treatment
✴Attenuated virus- weakened form of a virus; no
ability to cause disease


Treatment
✴Vector control


Treatment
✴Vector control
✴Drug therapy- interfere with DNA/RNA
synthesis


Treatment
✴Vector control
✴Drug therapy- interfere with DNA/RNA
synthesis
✴Acyclovir- blocks DNA polymerase

Viroids vs. Prions


Viroids vs. Prions
✴Viroids


Viroids vs. Prions
✴Viroids
✴Single-stranded
RNA


Viroids vs. Prions
✴Viroids
✴Single-stranded
RNA
✴Disrupt plant
metabolism


Viroids vs. Prions
✴Viroids
✴Single-stranded
RNA
✴Disrupt plant
metabolism
✴Coconuts,
oranges,
potatoes

Viroids vs. Prions
✴Viroids ✴Prions
✴Infectious
✴Single-stranded protein
RNA particles
✴Disrupt plant ✴Clump in brain;
metabolism cause cell
death
✴Coconuts,
✴Mad cow,
oranges, Creutzfeldt-
potatoes Jakob disease

Virology

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