Protein sorting through the Endoplasmic Reticulum

Signal Sequences

specific amino acid sequences that direct polypeptide localization

Post-translational Translocation

When a protein is translated in the cytosol and it travels to their final destination

Co-transitional Translocation

protein that is translated by a membrane-bound ribosome

the protein is being directly translated into the ER

Endoplasmic Reticulum

The largest organelle of the cell

Rough ER and Smooth ER

What are the two contiguous ER membrane domains?

Rough ER

covered in ribosomes, involved in protein synthesis and processing

common set

The ribosomes that synthesize co-translational and post-translational proteins come from a ___________ of ribosomes

Smooth ER

no ribosomes, instead it is involved in lipid metabolism and toxin detoxification

Water Soluble ER Proteins

will either stay in the lumen of the ER or will be secreted outside the cell

Transmembrane ER Proteins

will be localized to specific organelle membranes or the plasma membrane

Signal Peptidase

protein that cleaves the signal sequence of protein after translation termination

common set of ribosomes

ER proteins use a _____________ for protein translation

ER Signal Sequence

a hydrophobic part of the target ER protein that will bring the ribosome to the ER membrane

Signal Recognition Particle

Recognizes the ER signal sequence

Slow protein translation down until it recognizes the SRP receptor

Signal Recognition Particle Receptor

in the ER membrane and recognizes the SRP

Translocation of proteins into the ER lumen 1st Step

The signal recognition particle receptor guides and docks the ribosome to the ER membrane

Translocation of proteins into the ER lumen 2nd Step

the protein moves through a translocation channel in the ER membrane with its amino terminus head first

Translocation of proteins into the ER lumen 3rd Step

once the C-terminus of the ER targeted protein has passed through the channel, the signal sequence is then cleaved and the protein is released into the lumen of the ER

stop-transfer sequence

The transfer process of membrane proteins stop when the _________ is recognized by the channel

translocation; translation

Once the translocator recognizes the stop-transfer sequence, _______ is halted but ________ still continues

internal start-transfer sequence

Proteins that have multiple transmembrane passes have an ____________ which is not cleaved

True

SRP also recognizes internal start-transfer sequences

False

For a multiple transmembrane-pass proteins, the start-transfer sequence is cleaved