Lecture_13_and_14_Feb_3_and_5_

Lecture_13_and_14_Feb_3_and_5_ - Cytosol to ER Transport...

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1 Cytosol to ER Transport Reading Assignment: For 5 th Ed: 723-732
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2 Cytosol-to-ER Transport Structure and function of ER How is a cargo protein transported into the ER? What is the machinery mediating cytosol-to-ER transport?
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3 Structure of ER lipid bilayer membrane enclosing a lipid bilayer membrane enclosing a space called “ER lumen” isting in the forms of tubes and sacs existing in the forms of tubes and sacs throughout the cytosol tubes interconnected via three-way junctions constituting more than 50% of the total membrane in most cells a dynamic structure
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4 Dynamics of ER ER is a highly dynamic organelle (e.g. a potential role in neuronal signaling) ovie 12.4 Movie 12.4
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5 Two types of ER membrane domains polyribosomes attached no ribosomes attached where the biosynthesis of proteins takes place where the biosynthesis of lipids takes place
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6 “Rough” appearance of the rough ER is due to the presence of ribosomes on the ER membrane from the cytoplasmic side Note the presence of ribosomes on the nuclear outer membrane as well (remember that the nuclear outer membrane is connected to the ER)
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7 Polyribosomes Polyribosomes: multiple ribosomes translating a single mRNA at the same time. Polyribosomes are generated because another ribosome can start translation of a mRNA molecule before the previous ribosomes finish the translation (a yp g g p( common feature of mRNA translation) polyribosome nascent polypeptide chains of different lengths
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8 Different localizations of two pools of polyribosomes Depending on the nature of the translated proteins, there are two ools of polyribosomes in a cell Cytoplasmic polyribosomes: l ib t lt i pools of polyribosomes in a cell. Polyribosomes translating cytosolic proteins remain in the cytosol ER-associated polyribosomes: Polyribosomes translating a protein targeted to ER are recruited to the ER membrane from the cytosol (to be discussed later)
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9 Rough & smooth ER can be separated by their different densities homogenization: the process of breaking up a cell & making the lysate uniform microsomes: small vesicles generated from fragmented ER following homogenization sucrose gradient centrifugation: a type of centrifugation used to separate the subcellular structures based on their densities. creasing density increasing density Rough ER has a higher density due to its associated polyribosomes
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10 Functions of ER 1 .b iosynthesis of many proteins, including a. proteins secreted to the cell exterior b. transmembrane proteins on the PM c. Transmembrane or lumenal proteins of vesicular transport organelles, including ER, Golgi, creotory vesicles endosomes & lysosomes secreotory vesicles, endosomes, & lysosomes.
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This note was uploaded on 02/01/2010 for the course MCDB 103 taught by Professor Staff during the Winter '08 term at UCSB.

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Lecture_13_and_14_Feb_3_and_5_ - Cytosol to ER Transport...

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