Insulin, a protein that regulates blood sugar levels, is secreted from specialized pancreatic cells. Assume that you can track the cellular locations of these two proteins from the time that translation is complete until the proteins reach their final destinations. For each protein, identify its targeting pathway: the sequence of cellular locations in which the protein is found from when translation is complete until it reaches its final (functional) destination. (Note that if an organelle is listed in a pathway, the location implied is inside the organelle, not in the membrane that surrounds the organelle.) Hint 1. Comparison of free and bound ribosomes Eukaryotic cells contain two classes of ribosomes: those that float free in the cytoplasm and those that are bound on the cytoplasmic side of the rough ER. The ribosomes in these two classes are structurally identical. The only difference is that free ribosomes target the proteins they translate to the cytoplasm, whereas ribosomes bound to the rough ER target their proteins to the endomembrane system or to the exterior of the cell. a nonsense mutation resulting in early termination of translation a missense mutation causing a single amino acid change in the protein a silent mutation (no change in the amino acid sequence of the protein) a frameshift mutation causing extensive change in the amino acid sequence of the protein a frameshift mutation causing a single amino acid change in the protein
11/20/13 Chapter 17 assignment - Transcription, RNA processing, and Translation session.masteringbiology.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=2196984 30/68 Hint 2.How do proteins that will function in a cell’s endomembrane system and proteins that are secreted from the cell compare? What is the eventual (final) cellular location of proteins translated on free ribosomes? Review the animation showing the translation and secretion of insulin Transport between the membranes and compartments of the endomembrane system, including the plasma membrane, is via small vesicles that bud from one compartment and fuse with the next. The Golgi apparatus modifies and sorts proteins to be delivered to the endomembrane system, but does not modify and sort proteins to be secreted from the cell.
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