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2002 Exam 2 STAFF - BIOL 4374/BCHS 4313 Cell Biology Exam#2...

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1 BIOL 4374/BCHS 4313 Cell Biology Exam #2 October 30, 2002 SS#_____________________ Name_____________________ This exam is worth a total of 100 points. The number of points each question is worth is shown in parentheses. Good luck! 1. (3) A protein encoded by a nuclear gene has two N-terminal mitochondrial targeting sequences that are ultimately removed from the protein. In which mitochondrial compartment will this protein reside? Explain your answer. The first signal sequence will bring the protein through both outer and inner membranes to the lumen. The second signal sequence will bring the protein back through the inner membrane into the intermembrane space. 2. (2) Which characteristics describe a protein encoded by a nuclear gene that ultimately resides in the chloroplast stroma? answer - d a) Has an N-terminal signal sequence that binds to SRP b) Requires a pH gradient to enter as a folded protein c) Translated in the cytoplasm and has a C-terminal SKL sequence d) Translated in the cytoplasm and enters as an unfolded protein e) Crosses the inner and outer membranes simultaneously as a folded protein 3. (4) Describe the mechanism by which a nuclear protein is recognized and transported into the nucleus. 1) The protein has a nuclear localization sequence of >5 basic amino acids or two groups of 3 basic amino acids spaced <10 amino acids apart. 2) The nuclear localization sequence is bound by importins in the cytoplasm. 3) Importins a and b carry the protein into the nucleus through the nuclear pore. 4) Ran-GTP binds to importin b to release the protein in the nucleus.
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