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21 Cards in this Set
- Front
- Back
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Describe how retroviruses replicate.
Where does this process take place? |
1. Enter as RNA
2. Use RNA dependent DNA polymerase to reverse transcribe themselves to DNA 3. DNA is inserted into the host genome (provirus), then becomes latent. 4. DNA is later transcribed and translated Enters cytoplasm as RNA, then reverse transcribed and moves to nucleus as DNA. |
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Describe the Peyton-Rous virus.
Why does it work? |
Avian sarcoma virus, oncornavirus with oncogenes.
It depends on a cell in order for it to replicate, so it codes for oncogenes that stimulate cellular replication. |
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What are the three categories of retroviruses, what are some examples, how do they work and what do they cause?
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1) Oncornaviruses. HTLV-1, 2, 5. Transform and immortalize cells, cause cancer. (Onco, RNA)
2) Lentivirus - HIV-1 and 2. Slow, neurologic, or immunosuppressive. 3) Supmaviriae - not associated with human diseases |
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Describe an:
1. A-type retrovirus 2. B-type 3. C-type 4. D-type What are these types based on? Are all retroviruses enveloped? |
1. A-type - immature
2. B-type - spherical, off center capsid 3. Spherical, central capsid 4. Central, cone shaped cylindrical capsid Part morphology, part where their capsid is. Yes. |
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Give an example of C type and D type retroviruses.
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C type - HTLV.
D type - HIV |
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What are the unique characteristics of retroviruses?
1) Makeup 2) Contents in virion 3) What does a retrovirus become after it's integrated into DNA? |
1) Two copies of positive strand RNA
2) RNA-dependent DNA polymerase, tRNA, integrase (translocates DNA and puts it into genome) 3) Provirus (latent) - DNA intermediate |
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Describe the structure of a retrovirus envelope
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- derived from host plasma membrane
- contains viral proteins (spikes) that facilitate budding (cytoplasmic face) and new cell infections (extracellular face - receptors) |
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Describe the structure of the HTLV envelope and what each subunit does.
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gp62 gets split into gp46 and gp21.
Larger protein determines tropism - binds to cell surface receptors Smaller protein promotoes cell-cell fusion. |
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What's contained in the internal structure (nucleocapsid) of a retrovirus?
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- two identical copies of positive strand RNA virus
- multiple copies of reverse transcriptase - tRNA primers for reverse transcriptase enzyme |
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Retrovirus vs. central dogma
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Central dogma = DNA -> RNA -> protein
Retrovirus = RNA -> DNA -> RNA -> protein (RNA template and integration into DNA template after) |
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Where does retroviral replication take place?
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RNA virus - cytoplasmic at first (RNA -> DNA)
DNA integrated into host (provirus), nucleus, may be latent |
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What are the four major retroviral genes?
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1) GAG (group-specific antigen) - capsid, matrix, binding proteins
2) POL (polymerase) - polymerases, proteases, integrase 3) ENV - envelope glycoproteins, used for assembly/budding (cytoplasm), or receptor binding (extracellular face) 4) LTR - long terminal repeats - promoters, enhancers, bind cellular transcription factors |
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What are the oncogenes contained in HTLV?
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tax and rex (all HTLV genes end in x)
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What is tax and what does it promote?
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HTLV gene - activates transcription of genes like IL-2, IL-2R (
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What diseases are caused by HTLV-1, HTLV-2, and HTLV-5?
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HTLV-1 - ATL (acute T-cell lymphotic leukemia)
HTLV-2 - atypical hairy cell leukemia HTLV-5 - malignant cutaneous lymphoma |
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What regulatory proteins are contained in lentiviruses and HIV?
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tat, rev, nef
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Where does uncoating of retroviruses occur? What does ribonuclease H do?
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Cytoplasm - RNA is reverse transcribed, then ribonuclease H degrades RNA and synthesizes complimentary DNA (cDNA)
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Is reverse transcription error prone? How many mistakes are usually made? What does this rate of error mean?
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Yes, it's error prone - 1 error per 2,000 bases (huge error rate, means that retroviruses mutate quickly, create new strains quickly and create escape variants)
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Describe the process of integration of newly synthesized dsDNA, and what happens when it comes out of latency.
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Reverse transcribed in cytoplasm, delivered to nucleus, INTEGRASE integrates it into the host genome as a PROVIRUS where it can remain latent for years.
Comes out of latency, mRNA transcribed by host RNA polymerase II. Some mRNA translated to GAG, POL, ENV. |
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Describe virion release by budding.
Will release by budding kill cells? |
1) Budding - glycosylation binds capsid and other proteins to mRNA. Acylation of some proteins allow binding to glycoprotein spikes (env). Binding of two copies of virion and tRNA promotes viral budding and release.
May not kill cells - may form syncytia or multinucleated cells |
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Retroviral env gene:
1) What is it a remnant of? 2) What does it cause in cells? 3) What is it required for? |
1) Extinct retroviral infection
2) Early cell clumping and fusion 3) Uterine implantation and placental formation |
