110C LEC 14 Translation 3

110C LEC 14 Translation 3 - BCH 110C LECTURE 14 Translation...

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BCH 110C LECTURE 14 Translation 3 Lodish 6th ed. Pages 533-535; Chapters 13.1-13.3
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Many proteins need to get into membrane-bound compartments
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How do proteins cross or become inserted into membranes? • Membranes are substantial potential energy barriers for proteins. • negatively charged phospholipid head groups at the membrane surface make approaching it difficult for negatively charged proteins. • Inside of membrane is hydrophobic, and charged (hydrophilic) proteins cannot enter it.
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Radio-labeling studies demonstrated that secretory proteins are localized to the endoplasmic reticulum membrane shortly after synthesis.
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N-terminal signal sequence • At the N-terminal (beginning) of the protein • As it is synthesized the signal emerges from a channel in the ribosome (~35 aa are in the channel) • When the protein is ~70 amino acids long: • 13-36 amino acids (10-15 hydrophobic a.a.) are bound by the signal recognition particle (SRP) . • Different signals have different sequences • No consensus sequence
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Signal sequence for passage through the endoplasmic reticulum membrane
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Cell-free reconstitution experiments demonstrate that the translocation of secretory proteins into microsomes is coupled to translation What are microsomes? See slide 5
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(signal recognition particle) 6 protein subunits 300-nucleotide RNA 1. Cross-links to the signal sequence 2. Binds transiently to “ signal sequence ” on the nascent protein, the large ribosomal subunit
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This document was uploaded on 05/26/2011.

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110C LEC 14 Translation 3 - BCH 110C LECTURE 14 Translation...

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