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Biol 231 problem set key fall 2009 Q1. Eukaryotic cells have a number of membrane-bounded organelles with specific and essential functions in the life of the cell. For the list of organelles below, match each organelle to the best descriptions of their properties or functions that occur there. For each organelle there is more than one answer (exact number in brackets), and individual answers may apply to more than one organelle. Possible functions: (1) synthesizes membrane proteins and proteins to be secreted from the cell (2) covalently modifies proteins (3) sorts proteins to many other sites in the cell (4) maintains a pH much more acidic than that of cytoplasm (5) synthesizes sugar molecules using the energy of light (6) produces molecular oxygen by splitting water (7) consumes oxygen and releases carbon dioxide (8) synthesizes ATP from ADP and phosphate (9) site of genomic DNA replication (10) site of genomic DNA transcription into RNA (11) degrades proteins, lipids and nucleic acids (12) probably evolved from bacteria that were engulfed by the early eucaryotic cell ORGANELLE FUNCTIONS NUCLEUS 9, 10 MITOCHONDRION 7, 8, 12 CHLOROPLAST 5, 6, 12 ENDOPLASMIC RETICULUM 1, 2 GOLGI APPARATUS 2, 3 LYSOSOME 4, 11 [Hint: use your text book's glossary and the figures in chapter 1] Q2. You have approximately 10 cells in your body (human cells, that is - we'll come 13 back to the rest in a few weeks!). If all of those human cells arose by successive divisions of your original zygote, how many divisions did it take to produce you? Determine the integral number of divisions that gives the closest result Answer: Log2 of 10 is approximately 13 43 . So it would have taken 43 rounds of division starting with the original zygote to produce you (this would get you closest to 10 , with 8.80 x 13 10 cells). 12 Of course, the development of an adult organism from a zygote isn't quite that simple. In addition, things can go awry with cell division - notably the transformation of normal cells into cancer cells that divide in an uncontrolled way. If a single cancer cell in a tissue of the human body divides once every day, how long will it take for that cell to produce a tumor 20 cm in size (approximately equivalent to a golf ball)? Assume that 3 the original cell has a volume of 10 cm and determine the integral number of divisions ! 9 3 that gives the closest result. Answer: 10 cm x 2 = 20 cm -9 3 n 3 2 = 2 x 10 n 10 n = approx 34 divisions (resulting in a volume of 1.72 x 10 cm ), so 34 days total) 10 3 Q3. Cells can take up molecules from the outside world by endocytosis, through membrane channels, or by simple diffusion. But regardless of the avenue, the rate at which the cell can acquire material from the outside world is limited by the total surface area of the cell. On the other hand, the amount of material that they need to take up is proportional to the cell volume - i.e., how much biomass is in the cell. Some cells are spherical. (note: if you dont remember the formulae for surfaces and volumes of regularspherical.... View Full Document

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