Title: Rough%20Endoplasmic%20Reticulum
1Rough Endoplasmic Reticulum
Lecture 19 BSCI 420/421 Oct 16, 2002 If you
want the rainbow, you gotta put up with the
rain -Dolly Parton
2Fluorescent Micrographs of ER
3TEMs of RER
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6 F37 Free And Membrane- Bound R-somes
7The signal hypothesis That an ER signal sequence
in the nacent Polypeptide chain directs
8- Evidence for the signal hypothesis
- Without signal sequences, proteins are not
imported into RER. - (Protease protection assay)
- 2. When signal sequences are added to a gene
coding for a normally cytosolic protein, the
polypeptide it makes is incorporated into RER. - 3. A different sized (smaller) polypeptide is
made in RER than when the same mRNA is translated
on free polysomes in an - in vitro system (reticulocyte lysate wo RER).
9The ER Signal is a sequence of about 10
hydrophobic AAs That becomes anchored in the
membrane by hydrophylic AAs On either side.
E.g. Ser-leu-leu-leu-val-gly-Ile-leu-phe-trp-ala-
thr near the NH2 terminal The signal sequence
initially binds to a RNP particle called
the Signal Recognition Particle (SRP).
10How the SRP directs ribosomes to the RER
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12Evidence for an aqueous pore thru which the
polypeptide Passes into the ER
13A soluble protein released into the ER lumen to
be secreted
14A single-pass membrane protein
15Hydrophobicity plot of rhodopsin, a 7-pass
transmembrane protein