اهتحانات الشهادة الثانىية العاهة فرع علىم الحياة هسابقة في هادة علىم الحياة الودة: ثالث ساعات

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1 وزارة التربية والتعلين العالي الوديرية العاهة للتربية دائرة االهتحانات اهتحانات الشهادة الثانىية العاهة فرع علىم الحياة هسابقة في هادة علىم الحياة الودة: ثالث ساعات االسن: الرقن: دورة سنة 2009 العادية Answer the following questions Exercise 1 (5 pts) Duchene Myopathy is a degenerative disease of muscle fibers which is due to a gene carried on the non- homologous segment of chromosome X. Boys affected with myopathy do not synthesize the muscle protein, dystrophin, or synthesize an inactive form of dystrophin. Document 1 represents the pedigree of a family having one member of its family affected with the disease. 1-Determine, by referring to the pedigree, whether the allele responsible for the disease is dominant or recessive. 2-Indicate the genotypes of the parents. Justify the answer. 3-Determine the probability of the fetus to be affected. Parents (1&2) who are expecting a baby want to know whether their fetus is at risk of developing the disease. They consult a doctor who proposes a prenatal diagnostic test by applying Southern Blot technique. The results are shown in document 2. 4-Identify, by referring to document 1 and the autoradiography of document 2, the allele causing the disease. Justify the answer. 5-Specify the sex and the phenotype of the fetus. Justify the answer. Document 1 Document 2 A gene therapy is applied for the first time on mice attaining myopathy similar to Duchene myopathy in humans. This technique consists of injecting the dystrophin gene into a diseased organism by means of a virus vector which is harmless to mice Mice Results and human species. After this A. Normal Presence of fluorescence treatment, transversal sections are taken B. Myopathic, non-treated Absence of fluorescence from the diaphragm muscle (respiratory C. Myopathic, treated by Presence of fluorescence muscle) of 3 groups of mice ( A, B and injecting the dystrophin gene C); then incubated with anti-dystrophin through a virus vector fluorescent antibodies and observed Document 3 under a fluorescent microscope. The results obtained within weeks are shown in document 3.

2 Document 4 reveals the percentage of survival of the three groups of mice in function of time. 6- Interpret the results obtained in each of documents 3 and 4. What can be deduced about the efficiency of the used gene therapy? Survival Age (in weeks) Exercise 2 (5 pts) In an attempt to understand how the HIV that causes AIDS infects selectively T4 cells, we perform the following experiments on many lots of T4 cells (Lymphocytes characterized by the presence of CD4 proteins on their membranes) and T8 cells (lymphocytes characterized by the presence of CD8 proteins on their membranes). Document 1 presents the experimental procedure and the obtained results. 1-Interpret the obtained results. Studies and knowledge of the immune system and the immune reactions of persons infected by HIV allow for the preparation of an anti-hiv vaccine. We test the efficiency of this vaccine on Rhesus monkeys. Lot 1 Lot 2 Lot 3 Experimental Procedure T4 and T8 cells are placed directly in the presence of HIV T4 cells are incubated for 20 minutes with several types of antibodies* that do not bind to the membrane protein CD4, then placed with HIV T4 cells are incubated for 20 minutes with antibodies* that bind to the membrane protein CD4, then placed Results Infection of T4 cells, but no infection of T8 cells Infection of T4 cells only No infection of T4 cells with HIV *Anti-bodies block the biological activity of the molecules to which they bind Document 2 reveals the Document 1 variation of the proportion of T8 cells specific to HIV during infection time in vaccinated and nonvaccinated monkeys. Time (in weeks) Proportion of T8 specific for the HIV Lot 1 : Vaccinated monkeys (in a.u) Lot 2 : Non-vaccinated monkeys Exposure to HIV Document 2 2-Draw, on the same graph, the curves obtained from the tabulated data. 3-The immune response in the vaccinated monkeys is rapid and amplified. Refer to the results of document 2 to justify this affirmation. We measure the viral charge (the number of viral RNA copies /mm3 of plasma that is an indicator of the concentration of the virus in blood) in the vaccinated and non-vaccinated monkeys after 8 and 24 weeks of exposure to the virus. The results are shown in document 3. 4-Compare the obtained results and draw out a relation concerning the effect of the studied vaccine. Document 4 Viral charge (viral RNA copies/mm 3 of plasma) Vaccinated monkeys Non-Vaccinated monkeys Document 3 weeks weeks Time (in weeks)

3 Exercice 3 (5 pts) Nowadays, certain molecules that belong to the benzodiazepines family are used in treating anxiety. In order to study the action of these molecules on the muscular activity, we record by means of a microelectrode the electric activity of the postsynaptic motor neuron following the injection of GABA and/or benzodiazepine into the synaptic cleft using a micropipette. The experimental set up (a) and the results (b) are represented in document Determine, in reference to document 1, the nature of the studied synapse. Researchers found that rats administered a chemical substance, called picrotoxine, exhibit involuntary muscular contractions accompanied by signs of anxiety. 2- Specify the effect of picrotoxine and benzodiazepene at the level of this synapse. Justify your answer. Document 1 In order to understand thoroughly the mode of action of benzodiazepene, we measure the percentage of fixation of GABA on its receptors in function of the quantity of benzodiazepene injected into the synaptic cleft. The results are shown in document 2. Document 3 reveals the organization of the membrane receptor of a motor neuron in the spinal cord. Document 2 Document 3 3- Represent, in a table, the data shown in document What conclusions can be derived from the analysis of document 2? 5- Based on the information derived from all documents, explain the mode of action of benzodiazepene on the muscular activity.

4 Exercice 4 (5 pts) We realize a series of experiments to study the role played by certain body organs in response to glucose, insulin and glucagon. Experiment 1: We measure the variation of glycemia in the arteries and veins of a muscle and liver upon the injection of 235mg/min of glucose. The results are shown in documents 1 and 2. Document 1 Document 2 N.B: An artery brings blood to an organ and a vein takes blood away from an organ. 1-Interpret each of documents 1 and Use the acquired knowledge to indicate the document which corresponds to the activity of the liver. Justify the answer. Experiment 2: We inject labeled glucagon by a radioactive isotope into a normal mouse. The autoradiography of the hepatic cells of this mouse reveals the fixation of glucagon at certain points of the plasma membrane. However, the injection of labeled insulin by a radioactive isotope leads to a similar autoradiography but with different points of fixation of insulin on the plasma membrane. Experiment 3: Mutant mice show the following characteristics: obesity, chronic hyperglycemia and relative insensitivity to insulin injection that lowers glycemia very slightly. We remove hepatic cells from normal and obese (mutant) mice and place them, separately, in a medium containing radioactive insulin. Then, we purify the plasma membranes of these cells and measure the quantity of fixed insulin at the level of these membranes. The results are shown in document 3. 3-Analyze the results shown in document Based on the information provided by experiments 2 and 3 and the acquired knowledge, explain the origin of diabetes in the mutant mice. Document 3

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7 Exercise 3 (5 points) 1- Document 1 reveals that the injection of GABA alone provokes hyperpolarization (Ipsp), of an amplitude ~ 5mv that deviate the membrane potential away from the threshold of depolarization. This means that the synapse is inhibitory. (1 pt) 2- Benzodiazepine enhances the action of GABA, while picrotoxine inhibits its activity, because the injection of GABA and benzodiazepine provokes hyperpolarization of a higher amplitude (~6 mv) compared to that produced after the injection of GABA alone. picrotoxine increases the muscular contraction and the signs of anxiety, it favors the transmission of the nervous message and consequently it is excitatory. (1 pt) 3- Variation of the percentage of the fixation of GABA on its receptors as a function of the quantity of benzodiazepine injected in the synaptic cleft. (1 pt) Quantity of benzodiazepine in the synapse (nanomoles) Fixation of GABA (% in presence of benzodiazepine) The percentage of GABA fixation increase from 0 to 145% as the quantity of benzodiazepine increases from 1 to 1000 nanomoles. This indicates that the concentration of benzodiazepine favors the fixation of GABA and increase it s effect. (1 pt) 5- Document 3 that schematizes the structure of the postsynaptic receptor, reveals that the sites of fixation of GABA and benzodiazepine are close to each other and these sites are located on the same membrane structure: Cl - channel. The presence of benzodiazepine decreases the quantity of GABA indispensible for the opening of Cl - channel / or favors the opening of great number of Cl - channels that increases the entering of Cl - and consequently the inhibition of the nervous message, therefore the muscular contractions decrease. Exercise 4 (5 pts) 1- Document 1 reveals that before glucose injection at time 15 min, glycemia in the venous blood (1 g/l) is higher than glycemia in the arterial blood (0,9 g/l). Thus, the organ releases more glucose than it stores.) which means that the organ liberate glucose. However, glucose injection causes an increase in glycemia in both blood vessels but this increase is higher in the artery which reachs a value 1.6 g/l after 45 min following injection compared to 1,5g/L in the venous blood. This means the organ stores glucose in case of hyper glycemia (1 pt).

8 Document 2 reveals that before and after glucose injection, glycemia is always slightly higher in the arterial blood (~ 1.01 g/l) than in the venous blood (~ o.99 g/l). This means the organ only stores glucose. (1 pt) 2- Document 1 corresponds to the liver activity, because it is the only organ capable of storing and releasing glucose. The liberation of glucose happens before the 15 th min and after the 105 th min where glycemia is low and storage takes place between 35 th min and 105 th min when glycemia is high. (1 pt) 3- In normal mice, the quantity of fixed insulin on the plasma membrane increases from 0 to reach mol/mg of membrane proteins at 50 min. while, in obese mice the fixed quantity of insulin increases slightly to reach a maximum of mol/mg at 30 min. Beyond these values the fixed amount of insulin remains constant for the 2 mice but still higher in the normal mice than in obese mice. 4- Insulin can t have a hypoglycemic effect unless it is fixed on its specific receptors (exp. 2). In the obese mice, the quantity of insulin fixed on receptor is low (exp.3), this means that the origin of diabetes in obese mice is the low number of insulin receptors which reduce the hypoglycemic effect of insulin. Glucose will not be absorbed and stored by the hepatic cells, glucose remains in blood leading to chronic hyperglycemia. (1 pt)