Sunday, March 17, 2013
Prompt 2: Retroviruses and Big Idea 4
On page 148-149, Moalem talks about something called retroviruses. These are viruses that are made out of RNA and reproduce by transcribing themselves into DNA using reverse transcriptase. By reversing the transcription process, retroviruses are permanently integrated into the genetic material of an organism, which is passed down to the organism's offspring. Retroviruses relate to Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties, with the way they will graft its own genes into the host cell's DNA.
Describe the process of retrovirus replication. Also research a disease caused by a retrovirus (Adult T-cell Leukemia, Tropical Spastic Paraparesis, AIDS) and what is being used to treat the patients with the disease. How can retroviruses be dealt with when they integrate their genes into our own?
(Posted by Tina Tian, ttian4@students.d125.org)
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A retrovirus will use a host cell to replicate. Retroviruses contain viral RNA and have several copies of reverse transcriptase which is an enzyme that makes DNA from RNA. Once a DNA strand has been made from the viral RNA using reverse transcriptase, a complementary viral DNA strand is made. The double stranded viral DNA is then inserted into the host-cell’s chromosomes and the host-cell will express the viral DNA through transcription and translation. The host cell makes the viral proteins that make new copies of the retrovirus. The virus then buds from the plasma membrane of the host cell and is released into the organism’s body to infect more cells. On page 150, Dr. Moalem says “virus and organism become one and the same” which describes what happens when a retrovirus infects a cell, making the host-cell produce viral proteins. The idea of the interaction between retroviruses and host cells is related to big idea 4 which states “biological systems interact, and these systems and their interactions possess complex properties”.
ReplyDeleteTropical Spastic Paraparesis (TSP) is a disease caused by the human T-cell lymphotrophic virus type 1 (HTLV-1) retrovirus. The HTLV-1 retrovirus infects the spinal cord of the organism. The immune system’s response to the infection causes nerve damage which can cause the legs to gradually lose strength and flexibility. Other symptoms of the disease include deafness, double vision, facial paralysis, tingling sensations, spastic muscle movements and bladder abnormalities. The HTLV-1 virus can be spread from mother to child during pregnancy via the placenta, blood transfusions, contaminated needles, and sexual contact. The disease can remain undetected for years after infection. There is no cure for TSP yet.
While there is no cure for TSP, there are treatment options available to deal with the symptoms caused by the disease. Corticosteroids, man made drugs that closely resemble cortisol which is made by the adrenal glands, can help suppress the immune system so the immune response won’t damage the nerves. Oxybutynin, another drug, can help with urinary problems. Spastic muscle movements can be treated with lioresal or tizanidine. An article in “AIDS Research and Human Retroviruses” suggests that the anabolic steroid Danazol could also be a treatment of TSP. Danazol has been used to treat endometriosis, a medical condition in which cells from the lining of the uterus appear outside the uterine cavity. Scientists gave danazol to 6 patients with TSP, with 5 patients having a favorable response. Two patients began walking after having been confined to a wheelchair. Three patients were able to walk greater distances than prior to danazol. Urinary issues resolved in two patients. One patient did not tolerate danazol and one patient did not improve. Even though danazol didn’t help every patient, the majority of the patients improved.
TSP is not a fatal disease. People can live several decades after diagnosis with proper treatment and therapy. However, there isn’t a cure for TSP and there aren’t many cures for retrovirus diseases in general. Researchers are still experimenting and trying to find ways to stop retroviruses from physically entering cells. An article in the Huffington Post reports that researchers at Stanford University have created HIV-resistant T-cells by inactivating a receptor gene and inserting additional anti-HIV genes to block the HIV virus from entering a T-cell. If these cells work in humans, the immune system will not be destroyed by an infection from HIV providing for a potential cure of AIDS (another disease caused by a retrovirus). With this breakthrough, researchers continue to find new ways to stop a retrovirus before the retrovirus has a chance to integrate its genes into the host cell’s genes.
(Laura Gu, laugu4@students.d125.org)
In section 19.2, Campbell shows how retroviruses reproduce. First, glycoproteins on the virus envelope allow the virus to bind to the host cell. Next, the virus injects its RNA along with reverse transcriptase enzymes into the cell. Next, the RNA is changed into dual stranded DNA inside the cell. The DNA then merges with the cell’s DNA, and then through transcription and translation, the next generations of viruses are created in the cell without causing cell lyses. The new viruses then leave the cell, and go on to infect new cells. The book provides more evidence that retroviruses can do this, as Dr. Moalem states “8 percent of the human genome is composed of retroviruses,” (150). This relates to Big Idea one because these retroviruses in our DNA have given us selective advantages to survive and reproduce: the HERV viruses that exists in our DNA “may play an important role in the construction of a healthy placenta,” (150) which would help increase prenatal support to the child.
ReplyDeleteThe article “Can you explain AIDS and how it affects the immune system? How does HIV become AIDS?” talks about the virus HIV. This virus enters the DNA of CD4 Helper T cells, and reproduces from inside the DNA until the Helper T cells eventually die. As T cells die, it becomes harder for the body to respond to infection using the acquired immune response, which eventually causes the host to develop AIDS. Another infection can then go into a host and kill the person because there is no response from the acquired immune system. Unfortunately at the moment there is no known cure for the HIV retrovirus.
Retroviruses can be dealt with by the cytotoxic T-cells in our immune system. If a cell starts producing a protein that a Helper T-cell or cytotoxic T cell recognizes as non self, the cytotoxic T cell can send perforin and granzymes to kill the cell producing the retrovirus proteins, stopping reproduction of the virus. Helper T cells can call in cytotoxic T cells with cytokines to kill the retrovirus-infested body cells.
I agree with Laura’s description of how viruses replicate. Her findings that TSP has no cure shows that it is not easy to destroy all cells with provirus in their DNA and also stop the copying of retroviruses, regardless of what cells the virus reside in. The fact that Laura found an article showing there are some drugs that can relieve symptoms, but it is a poor sign that there is no cure. It is possible that a cure for this disease could help researchers find a cure for HIV. Also her article on HIV resistant T-cells shows that retroviruses can be stopped before they even enter a cell, which opens a new door on how to treat retroviruses.
Woodward, William C. "Can You Explain AIDS and How It Affects the Immune System? How Does HIV Become AIDS?: Scientific American." Can You Explain AIDS and How It Affects the Immune System? How Does HIV Become AIDS?: Scientific American. N.p., 8 Nov. 1999. Web. 17 Apr. 2013.
(Zachary Rane, zrane3@students.d125.org)