Lecture7

Lecture7 - 01.28.11 Lecture 7 Intracellular compartments...

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01.28.11 Lecture 7 - Intracellular compartments and transport II
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Review of protein translocation
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1. The secretory pathway: how newly made lipids, proteins, and carbohydrates are delivered to the cell surface via exocytosis 2. Endocytic pathways: how cells take up fluids and particles (large and small) from the extracellular environment Exocytosis & endocytosis
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Most (or all) proteins are covalently modified in the ER 1. Formation of disulfide bonds between cysteine residues of the same polypeptide (intra-molecular) or different polypeptides (inter-molecular) 2. Addition of short oligosaccharide side chains (glycosylation )
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Formation of disulfide bonds occurs within the ER Oxidation of pairs of cysteine side chains Reaction can’t occur in the cytoplasm
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Example: antibodies
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Many proteins are glycosylated in the ER 1. Polypeptide is translocated into ER lumen 2. Pre-formed, branched oligosaccharide (14 sugars) transferred en bloc from dolichol (a specialized lipid) to specific sequence 3. Sequence contains asparagine - N-linked 4. Reaction catalyzed by oligosaccharide protein transferase (active site oriented towards lumen)
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Lecture7 - 01.28.11 Lecture 7 Intracellular compartments...

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