Molecular and Cell Biology Final Review

Molecular and Cell Biology Final Review - Molecular and...

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Molecular and Cell Biology Final Review NEW SHIT Chpt. 15 – Intracellular Compartments and Transport Basic Shit About Protein Sorting: o Proteins are imported into organelles by three mechanisms: Proteins moving from the cytosol to the nucleus through nuclear pores Proteins moving the cytosol to an organelle across the membrane 1. Cytosol ER, Mitochondria/Chloroplast, Peroxisome Proteins moving by transport vesicles 2. ER Lumen 2 nd Membrane o Signal Sequences: Sorting signal on protein that is often removed from the finished protein once the sorting decisions have been executed Directs a protein to a particular organelle Proteins Enter the Nucleus Through Nuclear Pores: o Nuclear envelope is perforated by nuclear pores that form gates through which all molecules enter/leave o Direction of Traffic Both Directions Nucleus Cytosol Cytosol Nucleus Proteins synthesized in the cytosol destined for the nucleus Ribosomal subunits synthesized in the nucleus destined for cytosol o Size/Structure Contains one ore more water-filled channels through which small water soluble molecules can move freely Large molecules need to carry appropriate sorting signal o Signal Sequence Nuclear Localization Signal Directions protein from cytosol into nucleus o Mechanism for Import Active transport of proteins through nuclear pore 1. Cytosolic proteins called nuclear transport receptors bind to nuclear protein 2. Complex is guided to a nuclear pore by the fibrils that extend from the pore 3. Nuclear protein bound with the receptor is actively transported into the nucleus by hydrolysis of GTP 4. Receptor is exported back to the cytosol for reuse o Mechanism for Export Similar mechanism is used for mRNA, but in the opposite direction o Uniqueness Transport proteins in their fully folded conformation Transport ribosomal subunits as assembled particles o Summary NTR + Nuclear Protein Guided to nuclear pore Transported Receptor goes back into the cytosol Proteins Unfold to Enter the Mitochondria and Chloroplasts o Proteins contain a sequence at the N-terminus that direct it to the mitochondria or chloroplast o Translocated simultaneously across both inner and outer membranes, at specialized sites, where both membranes are in contact o Mechanism Proteins Unfold to Enter 1. Signal sequence is recognized by a receptor in the outer membrane 2. complex of receptor and protein diffuse laterally to a contact site where the protein is translocated across both membranes by a protein translocator 3. Signal sequence is cleaved off Proteins Enter the Endoplasmic Reticulum While Being Synthesized o Serves as an entry point for proteins destined for other organelles o Enter ER Transport Vesicle Organelle o Two kinds of proteins: 1. Water-Soluble Proteins that are translated across and enter the lumen that are destined for either secretion or for the lumen of an organelle
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This note was uploaded on 03/28/2008 for the course BIOL 213 taught by Professor Mcknight during the Fall '07 term at Texas A&M.

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Molecular and Cell Biology Final Review - Molecular and...

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