Virology

Virology

Tuesday, January 26, 2010

Virus


Virus ✴Particle made of nucleic acid and a protein coat



✴~100x smaller than our cells



✴~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

✴They have nucleic acids (DNA or RNA)✴No membrane bound organelles


You Be the Judge

✴They have nucleic acids (DNA or RNA)✴No membrane bound organelles✴They cannot metabolize or divide


You Be the Judge

✴They have nucleic acids (DNA or RNA)✴No membrane bound organelles✴They cannot metabolize or divide✴Must use a host to reproduce


Structure


Structure✴Nucleic acid surrounded by a capsid

coat



coat✴4 types:



coat✴4 types: ✴helical



coat✴4 types: ✴helical✴icosahedral



coat✴4 types: ✴helical✴icosahedral✴enveloped



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✴Appear spherical at low mag.✴They actually have 20 triangular sides


Icosahedral Virus✴Appear spherical at low mag.✴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



membrane, forming an envelope✴Glycoproteins (“receptors”) on the surface

of the envelope allow the virus to appear “friendly”



membrane, forming an envelope✴Glycoproteins (“receptors”) on the surface

of the envelope allow the virus to appear “friendly”

✴HIV, influenza


Enveloped Virus


Bacteriophage“Complex Viruses”



✴Hexagonal head bound to a helical tail



✴Hexagonal head bound to a helical tail✴Resemble a lunar landing pod



✴Hexagonal head bound to a helical tail✴Resemble a lunar landing pod✴Tail fibers act (“legs”) help to inject DNA

into the host cell



✴Hexagonal head bound to a helical tail✴Resemble a lunar landing pod✴Tail fibers act (“legs”) help to inject DNA

into the host cell✴T Phages (E.coli)


Bacteriophage


Bacteriophage Replication



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




✴Viruses that replicate this way are known as virulent




✴Viruses that replicate this way are known as virulent

✴T phages are virulentTuesday, January 26, 2010


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




wThis type of virus is known as a temperate virus




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:✴Some DNA enters a host and makes mRNA✴Other DNA may actually insert into a host

cell’s chromosome (provirus)



cell’s chromosome (provirus)✴RNA Viruses:



cell’s chromosome (provirus)✴RNA Viruses:✴Some RNA enters the host and serves

directly as RNA



cell’s chromosome (provirus)✴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


VirologyPart Deux


Human Viral Diseases


Human Viral Diseases✴Because viruses aren’t “alive” they must

be spread by an intermediate host (vector)


Chicken Pox/Shingles:


Chicken Pox/Shingles:✴Caused by vericella-zoster herpesvirus


Chicken Pox/Shingles:✴Caused by vericella-zoster herpesvirus✴Spread through the air and contact


Chicken Pox/Shingles:✴Caused by vericella-zoster herpesvirus✴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



by 5 different viruses✴A and E spread by fecal matter



by 5 different viruses✴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✴Acquired Immune Deficiency Syndrome✴Caused by the HIV virus


AIDS✴Acquired Immune Deficiency Syndrome✴Caused by the HIV virus✴Glycoproteins on the surface of the virus

bind to receptor sites of immune cells (macrophages)




✴Retrovirus, Provirus




✴Retrovirus, Provirus✴Genetically diverse


Is there a cure ?


Is there a cure ?✴Azydothymidine- inhibits reverse

transcriptase



transcriptase ✴Protease inibitors- blocks synthesis of

new capsids



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



populations✴Rainforest animals-> Ebola



populations✴Rainforest animals-> Ebola✴Hanta virus (pneumonia)-> mice



populations✴Rainforest animals-> Ebola✴Hanta virus (pneumonia)-> mice✴SARS-> civet cats


✴Epidemic- quickly spreading infectious disease



✴Pandemic- disease spreads over large regions



✴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)



build an immune response (microevolution)✴Inactivated virus- not able to replicate



build an immune response (microevolution)✴Inactivated virus- not able to replicate✴Attenuated virus- weakened form of a virus; no

ability to cause disease




ability to cause disease✴Vector control




ability to cause disease✴Vector control✴Drug therapy- interfere with DNA/RNA

synthesis




ability to cause disease✴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


RNA ✴Disrupt plant

metabolism


Viroids vs. Prions



metabolism✴Coconuts,

oranges, potatoes


Viroids vs. Prions



metabolism✴Coconuts,

oranges, potatoes

✴Prions✴Infectious

protein particles

✴Clump in brain; cause cell death

✴Mad cow, Creutzfeldt-Jakob disease


Virology

Education

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