Soluble Protein Import into the Endoplasmic Reticulum Flashcards
All protein synthesis begins with
Free cytosolic riboosomes
What does the Endoplasmic Reticulum Signal Sequence contain?
Non-Polar amino Acids (Hydrophobic) on the N-Terminus of a polypeptide
Free cytosolic ribosomes are brought to _____ _______ where is will continue to polypeptide synthesis
Endoplasmic Reticulum
Free Cytosolic Ribosomes with the appropriate signal sequence can…
Be transported to the Nucleus and Mitocondria
If free ribosomes shave no signal sequence, where do they transport?
If there is no signal sequence the free ribosomes remain in the cytoplasm
Membrane-bound Ribosomes (Bound to the ER) with the appropriate signal sequence can be transported to…
From the endoplasmic Reticulum, the proteins can be transported to the Golgi Apparatus, Lysosomes, Plasma Membrane, or be secretory vesicles
What directs the Free Cytosolic Ribosomes to the ER?
An ER Signal Sequence and SRP
Signal Recognition Particle:
Binds ER single sequence of Protein being transported, and translation is paused
SRP Receptor
is a transmembrane protein in the ER whose cytosolic side recognizes SRP for binding. the SRP particle is removed
Nascent: Protein Translocator
The polypeptide is threaded into the lumen via a translocation channel and translation resumes
Signal Peptidase
when the polypeptide is through the translocator, the translocator closes and the enzyme cleaves the signal sequence from the N-Terminus of the polypeptide
When the signal sequence is cleaved
The polypeptide will continue to fold in the ER lumen
Do chaperone proteins play a role in ER Import?
yes, the chaperone proteins in the ER help proteins fold into their correct conformation and prevent misfolded proteins from exiting the ER
UPR: Unfolded Protein Response:
Accumulation of Misfolded proteins in the ER results in more production of Chaperones.
- The cell will inhibit protein synthesis and UPR will slow translation and also activate genes that encode for chaperone proteins
Are proteins folded in the cytosol before import or in the ER Lumen after import?
Folded when they enter the ER Lumen
where is the Signal Sequence on the ER Protein?
N-Terminus
-includes a string of hydrophobic amino acids
how does the Er recognize incoming ER proteins? What is responsible and where is it located?
Signal recognition particle bring protein to the ER and binds to the SRP Receptor
What is the function of the translocator?
to bring the polypeptide into the ER Lumen
ER Signal Sequence
Hydrophobic amino acids for soluble proteins on the N-Terminus
Is signal sequence cleaved?
yes, it is cleaved by signal peptidase enzyme
Is the protein imported in a folded or linear conformation?
Protein is imported in a Linear Conformation
What are the proteins required of ER Transport?
-Signal recognition particle
-SRP Receptor
-Translocator
-Signal Peptidase
-Chaperones
Is energy required for this process?
No
