Turn over 17 6 The neurones of the central nervous system contain TAU proteins. These proteins help to maintain cell structure. In humans, six different TAU proteins can be produced from a single gene. Parkinson’s disease has been linked to the different forms of the TAU proteins present in neurones. Scientists are studying the effect of these different TAU proteins in animal models. One model used is the fruit fly, Drosophila. (a) Describe how Drosophila flies could be genetically modified to produce one form of the human TAU protein. 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Flies making different forms of human TAU protein were tested in a climbing test. •  Fifteen one-day-old Drosophila flies were placed at the bottom of a measuring cylinder. •  A video recording was carried out and paused at 10 seconds. The height climbed by each fly was recorded. •  The test was repeated for flies of different ages. mean height climbed time = 0 seconds time = 10 seconds The table shows the results of this investigation. Age of flies / days Mean height climbed at 10 seconds / mm Control (no human TAU protein) 0N3R TAU protein 0N4R TAU protein 1 60 ± 6 52 ± 5 54 ± 5 7 61 ± 4 43 ± 1 50 ± 4 14 53 ± 3 18 ± 2 28 ± 8 21 45 ± 9 12 ± 4 18 ± 5 28 32± 8 10 ± 5 19 ± 1 35 26 ± 9 3 ± 1 11 ± 1 42 15 ± 3 1 ± 1 3 ± 1 Turn over 19 Comment on the effect of TAU proteins on the ability of Drosophila flies to climb. 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The length of time between impulses was measured for Drosophila flies of different ages. The results are shown in the graph. 9 8 7 6 5 4 3 2 1 0 Length of time between impulses / ms control 0N3R 0N4R Key Age of flies / days 10 45 Determine the effect of these TAU proteins on the maximum frequency at which nerve impulses can be conducted along the axon of the neurone. 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(Total for Question 6 = 11 marks) Turn over 21 BLANK PAGE 22 *7 Humans are complex multicellular organisms. Cell division is involved in: •  the production of gametes •  the development of tissues •  the development of tumours •  the response to infection in humans. The figure summarises some information about the organisation of cells in a human. More than 3.7 × 1013 cells in one human More than 200 different cell types The typical cell cycle for a human cell is about 24 hours. However, some cells can divide every eight minutes and others do not divide at all. Four main tissue types (each with many ‘sub-types’) At least 79 different organs Eleven different organ systems The table summarises some information about human genetics and cancers. Number of protein coding genes Approximately 20 000 Number of different genetic disorders Approximately 2200 Proportion of cancers caused by an inherited genetic defect 5 to 10% Turn over 23 Evaluate the role of cell division in processes affecting human health and disease. 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(Total for Question 7 = 9 marks)