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Prob2 - 12-1 You are studying a protein that normally...

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12-1 You are studying a protein that normally resides in the plasma membrane. The organization of this protein is depicted in Figure Q12-1, where the gray boxes labeled A, B, and C represent transmembrane regions and the segments labeled 1, 2, 3, and 4 represent the portions of the protein between the transmembrane regions. Figure Q12-1 If you also know that segments 2 and 4 contain N-linked oligosaccharides, draw the topology of the protein as it is inserted in the plasma membrane. Be sure to label the cytoplasmic and extracellular face of your membrane and the N-terminus and C-terminus of your protein. ANS: 12-8 State whether the following proteins are being translated on ribosomes attached to the ER, and explain your answer. A. A protein that resides in the mitochondria. (Cross out) B. A protein that resides in an endosome. C. A protein that will be secreted into the extracellular space. D. A nuclear protein. (Cross out) E. A protein linked to the plasma membrane by a GPI anchor. F. A protein that resides between the inner and outer nuclear membranes ANS: 11-10 Why are glycolipids found on the extracellular, but not the cytoplasmic, surface of the plasma membrane? (a) Flippases transport them from the cytosolic face. (b) The enzymes that produce them are present only on the extracellular surface of the plasma membrane. (c) The enzymes that add the sugar groups are confined to the inside of the endoplasmic reticulum and the Golgi apparatus. (d) The oligosaccharides on glycolipids are cleaved off by enzymes found only in the cytosol.
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(e) They flip spontaneously, after incorporation, due to the hydrophilic sugar head groups.
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