7.012 Final Review Session (Lectures 32-38) HIV & AIDS 1) HIV can lie dormant (“hidden”) in a person’s body for many years without causing any noticeable symptoms. a) Explain how an unrelated infection that activates the humoral response pathway may lead to development of a full-blown HIV infection. Although HIV infection does not directly cause death, it eventually allows for opportunistic infections, which are often the cause of death in AIDS patients. Uninfected individuals can clear such infections with no problem. b) Why aren’t these infections cleared efficiently in AIDS patients? 2) HIV is a retrovirus and its genome is a single (+) strand RNA. Two copies of this RNA genome are packaged with two copies of the retroviral enzyme, reverse transcriptase, within a protein capsid. This capsid is further packaged into an envelope derived from the plasma membrane of the host cell in which the virus was formed. The surface of the envelope is covered with an envelope glycoprotein, called gp120. a) HIV specifically infects the helper T cells of the human immune system. If receptor-ligand mediated viral entry is the means by which HIV enters TH cells, what would be the most likely ligand on HIV? b) Once infection has taken place, the RNA genome has to be made into double-stranded DNA. This process is mediated by reverse transcriptase. Once a double-stranded DNA copy of the HIV genome has been made, it is integrated into the host cell genome. The integration event is mediated by the enzyme integrase. i) What are the three steps required to produce double-stranded DNA from the single (+) strand RNA genome?ii) The central dogma states that: DNA RNA Protein Which one of the enzymatic activities possessed by reverse transcriptase goes against the central dogma. Explain your answer. Stem Cells A scientist finds a new brightly colored mammalian species, which she names Magnificus colores. She isolates blue and green cells from different parts of this organism, and cultures each cell individually. a) Are the blue cells stem cells? Why or why not? b) Given that the green cell is a stem cell, can you tell whether it is totipotent or pluripotent? Explain your answer. c) The scientist finds out that development in M. colores is similar to human development. She wants to obtain a single cell that can give rise to an individual M. colores. Do you have any suggestions? What is the property that this cell must possess?d) She now wants to isolate embryonic stem cells from an M. colores embryo. Where exactly in a developing embryo can she find such cells? e) M. colores have coats with multi-colored spots, which are produced by the Speckle gene. One functional copy of Speckle is sufficient to give multi-colored spots. While studying different embryos, the scientist detects that one 8-cell stage embryo has both copies of Speckle mutated. Suggest a strategy using stem cells by which she could try to rescue this defect in the embryo. f) One of the M. colores has a weak heart that has only 10% of the normal functioning capacity. If technology were advanced enough, how could ES cells from this animal potentially be used to save it from heart failure? Why would this be preferred over a heart transplant such as those performed today? Cloning A rare species of monkeys are close to extinction, and as a scientist you have been asked to assist with the cloning of this species in order to increase its numbers. You decide to clone the monkeys in the same manner as Dolly the sheep was cloned. One of the last healthy monkeys, KoJo, recently died in a fire and no remains were found. Because KoJo was an extremely healthy animal, you would ideally like to clone her instead of another monkey. a) Is it possible to clone KoJo? b) A few weeks later you remember that KoJo had a fraternal twin, JoKo. Could KoJo be cloned from JoKo? Why or why not? c) Kojo’s sister, Mimi, had two faulty kidneys and so KoJo, when she was alive, donated one of her kidneys to Mimi. Explain how Mimi could be useful for cloning KoJo.d) You observe some strange symptoms in the clone of KoJo such as generalized weakness, loss of motor skills, and loss of appetite. You suspect that this is a genetic disorder, but KoJo did not display any of these symptoms during her lifetime. Given this information, why is the clone so sick? e) It turns out that some of KoJo’s oocytes were frozen back at the breeding facility. Could the nuclei in these oocytes be used to clone KoJo? f) In case cloning with the nuclei from Kojo’s oocytes doesn’t work out, you decide to use the procedure involving Mimi again, but this time you want to be sure the clone doesn’t exhibit the symptoms described above. Given all the available information, how might you proceed with the cloning experiment? g) Will these clones produced in (f) have the same temperament, IQ, or eating habits as KoJo? Molecular Evolution 1) There are a number of forces that drive evolution. Below are descriptions of forces involved in evolution. Read each description and answer the questions. a) Mutations in the human genome can spontaneously arise from errors made by the DNA replication machinery and from exposure to environmental mutagenic agents. In which type of cells in the body must these mutations arise in order for them to affect the evolutionary direction of a species? b) Due to environmental pressures (e.g. predators, weather, food supply, etc.) not all individuals in a population will be able to reproduce as successfully as others in that same population because of the variability in the population which arises from mutation. What is this differential reproductive success called, and how can it be a driving force behind evolution?c) Occasionally populations of individuals will be divided by insurmountable physical obstacles such as rivers, oceans, mountains, etc. How can such obstacles be a driving force of evolution? When studying evolution at a molecular level , one looks at DNA and protein sequences. Below are three amino acid sequences from a chicken, an iguana, and a chimpanzee that represent an important domain of a protease. 1) NH3+...ACEGGLYSSFDEVRHHKESRGCP...CO2- 2) NH3+...ACDEGIYSKGDEVRHHKESEGCR...CO2- 3) NH3+...ACRGGLYSSFDEVRHLKESRGCS...CO2- d) Which amino acids in the above sequences are likely to be important for the function of
View Full Document
Unlocking...