Micro Chap 13/Exam 4
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How are viruses different from bacteria and other organisms?
- Viruses are acellular and ametabolic
- -cannot reproduce without a host cell
Name 5 Diseases caused by viruses
What is the structure of a virus?
- composed of a protein coat, with spikes. Some contain an envelope. The genes of nucleic acid are inside the protein coat
What is the function of the nucleic acid?
DNA or RNA, about 5-50 genes
What is the function of the capsid and capsomere?
- capsomere: a protein molecule
- capsid: the whole protein coat
What is the function of the envelope?
phospholipid bilayer--> the virus gets this from the host cell
What is the function of the spikes?
There are two types of spikes:
- 1. Neuraminidase: allows viron to exit the cell-"N" spikes
- 2.Hemoglutinin: attach virus to the host- "H"spikes
How do helical and polyhedral viruses differ?
- The shape of the capsule
How would you culture animal viruses in the laboratory using eggs?
- viruses require live host cells
- --> embryonated eggs
- ->they are full of live bird cells
- --> grow the virus in the egg, incubate it, crack the egg and you have the virus
*most flu vaccines today are grown in bird eggs
How would you culture animal viruses in the laboratory without using eggs?
- An animal cell culture
- 1. a tissue from a live animal is treated with enzymes to separate the cells
- 2. Cells are suspended in a liquid culture medium to be kept alive
- 3. Normal cells or primary cells grow in a monolayer across the bottom of the plate
- -->transformed cells or continuous cell cultures do not grow in a monolayer but a cytopathic effect
How is a virus infection identified in an animal?
- 1. Symptomatically
- 2. ELISA
- 3. Viral Nucleic Acid detection tests
What is the viral multiplication cycle?
- 1. Attachment
- -viral surface proteins bind to the surface proteins (act as receptors)on host cells (viruses are nonmotile so this happens at random)
- -this is like a lock and key mechanism
the viral nucleic acid enters the host cells
- 3. Biosynthesis: the host cell's transcription and translation machinery will transcribe and translate the virus' genes
- -A viron has both early and late genes
- *Early Genes- code for NA replication enzymes (polymerases) resulting in many viral NA molecults
- *Late Genes- code for capsomeres, spikes, and assembly enzymes resulting in the host cell containing all of these parts
- 4. Assembly: assembly enzymes catalyze reactions that put the viral bits together
- -now, the host cell contains many new virons
- 5. Release
- -some viruses have very late genes that code for enzymes that will kill and lyse the host cell
- -many enveloped viruses are "budded" out of the host cell
Why is the host cell almost certainly doomed?
- Viral replication will kill the cell unless...
- -a natural killer cell or killer T cell find the cell first and kills it
*host cell still doomed
What causes the symptoms of a viral infection?
- -Type of host cell attacked
- -chemicals that are secreted by and activated white blood cells
What makes a retrovirus so special?
- 1. RNA genes
- 2. Enzymes called reverse transcriptase
What is the multiplication cycle of a retrovirus?
- Once the virus attaches to the cell...
- 1. the reverse transcriptase matches DNA to the Virus's RNA creating viral DNA
- 2.The new viral DNA is transported into the host cell's nucleus
- -here, it is integrated into the host cell's chromosome as a provirus by viral integrase
- *the viral DNA may now be replicated when the host cell replicates
- 3. Transcription of the provirus will produce RNA for new retrovirus genomes and RNA that encodes for the retrovirus capsids, enzymes, and envelope proteins
What is the structure of HIV?
- *2 strands RNA
- * 2 reverse transcriptase molecules
Where, when, and how do we think HIV originated?
Western and central Africa in the 1930's
A simian immunodeficiency virus experienced a mutation that allowed it to infect humans. The virus probably first infected humans who killed and butchered monkeys harboring the virus
What kind of cell is a host cell for HIV? What features allow this?
- Human cells which care both CD4 and either CCR5 or CXCR4 co-receptors
- -such cells seem to be limited to helper T lymphocytes, macrophages, and dendritic cells (which are macrophage like cells found in mucosal tissues)
HIV's g120 spikes bind to the receptor and co-receptor on these human cells
How is an HIV infection diagnosed?
- *indirect ELISAS which test for the antibodies
- -since it takes a little time for these to show up, a person could be recently infected and test negative
confirmatory tests include western blot to look for proteins or tests which detect HIV nucleic acid in blood
How is HIV transmitted?
- -Blood to Blood contact
- -Sexual intercourse
- -Mother to fetus (preventable with medicine)
- -Breast Milk
Why does a person with AIDS suffer all sorts of opportunistic infections and cancers and ultimately die of them?
Their immune system has been compromised and they cannot fight off these infections
How do fusion inhibitors work to interrupt the HIV multiplication cycle?
Prevent attachment of the virus
How do integrase inhibitors work to interrupt the HIV multiplication cycle?
inhibit the viral DNA from being integrated into the host cell's chromosome as a provirus
How do reverse transcriptase inhibitors work to interrupt the HIV multiplication cycle?
inhibits the reverse transcriptase enzymes from creating viral DNA
What is HAART?
- High Activity AntiRetroviral Therapy
- -3 reverse transcriptase inhibitors of 2 different classes or
- -2 reverse transcriptase inhibitors plus 1 HIV protease inhibitor
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