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Protein Targetting and the lac Operon

1.How are proteins targeted to different compartments with in a eukaryotic cell? Please give a detailed example of how a protein is targeted to a specific organelle.

2.Please describe, in depth, the regulation of the lac operon.

Solution Preview

The attached file: Cell_Biology_QuestionsIII.doc. covers both protein transport in eukaryotes including regulation of the lac operon.

HOW ARE PROTEINS TARGETED TO DIFFERENT COMPARTMENTS WITH IN A EUKARYOTIC CELL? PLEASE GIVE A DETAILED EXAMPLE OF HOW A PROTEIN IS TARGETED TO A SPECIFIC ORGANELLE.

Protein targeting is a mechanism by which specific proteins are shuttled to specific locations within a cell. Such targets include the interiors (lumen) of many organelles, the plasma membrane, as well as secretion to the cells exterior. Two different signals direct a given protein's movement through the system, and thereby determine its location in the cell, are intrinsically encoded within the protein itself. These signals include signal peptides and signal patches. Signal peptides are a small continuous stretch of 15-60 amino acids that tells the cell's transport apparatus where it is to be localized such as the mitochondria and ER. Signal patches on the other hand rely on the 3D structure of the protein because the amino acids that comprise the patch are distributed across the across the linear sequence of the protein and must be properly align during protein folding to create a functional patch. Signal patches are believed to play a role in the sorting of proteins to the lysosome.

Proteins move between compartments in two fundamentally different ways. First, they may be translocated across a lipid membrane via a protein translocator in which case the protein must be an unfolded state in order to pass through the membrane. A good example is protein translocation across the ER membrane (called cotranslational protein translocation). The N-terminal signal sequence of a protein, as it emerges from the ribosome, is ...

Solution Summary

This solution covers protein targeting in eukaryotes and uses mitochondrial transport as an example. The second half of this solution introduces the lac operon and its role in lactose metabolism is regulated.

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