BIO 320 Lec5.2009 - Bio320 Cell Biology Lecture 5 Membrane...

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Bio320: Cell Biology Lecture 5 (2/3/09) Membrane Trafficking: Overview of Secretory Pathway, Signal Peptide Hypothesis, Stop- transfer Sequences and the Endoplasmic Reticulum . Reading : Alberts 5 th edition: pages 723-748. Learning Objectives When you have finished this lecture and the assigned reading, you should be able to: 1. Explain the structural and functional relationship between the endoplasmic reticulum (rough and smooth) , Golgi complexes, lysosomes, endosomes, vacuoles and plasma membranes of eukaryotic cells. a. Describe the pathway of proteins destined for secretion, starting with synthesis and ending with exocytosis (secretion). Describe the pathway of membrane proteins. b. Point out the differences between the syntheses of secretory/integral membrane proteins and cytosolic proteins. c. Explain the difference between “bound” and “free” ribosomes. Which ribosomes are used for different kinds of proteins? 2. Summarize the mechanisms whereby newly synthesized proteins are targeted and sorted for their appropriate destinations. 3. Understand how sorting signals are used to traffic proteins. 4. Understand the how the signal peptides, SRP and the SRP receptor direct nascent mRNAs for secretory proteins to the ER. 5. Describe and understand how the combination and placement of signal peptides, the charges around the signal peptide, the presence of cleavage site(s) for signal peptidase, and stop-transfer sequences in a polypeptide chain can determine the orientation of 5 kinds of polypeptides in the secretory path. Describe how these sequences can determine whether a protein is: (a) a secretory protein (b) an integral membrane protein with its amino-terminus on the cytosolic side of the membrane (c) an integral membrane protein with its carboxyl-terminus on the cytosolic side of the membrane (d) an integral membrane protein that spans the membrane several times with its carboxyl-terminus on the cytosolic side of the membrane (e) an integral membrane protein that spans the membrane several times with its carboxyl-terminus on the cytosolic side of the membrane Outline of Background for Lecture The Dynamic Nature of the Endomembrane System I. Introduction A. Membranes divide the cytoplasm of eukaryotic cells into distinct compartments.
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