Exam 5 Flashcards
what is Co-translational translocation
Protein sorting during translation (e.g., rER)
what is Vesicular transport
Transport of proteins in secretory and endocytic pathways
protein targeting in co-translational translocation overview
protein synthesis on cytoplasmic ribosomes > secretory and membrane proteins targeted to rER by sorting signals > co-translational translocation takes place at rER membrane > protein folding and quality control in rER lumen > vesicular trafficking to golgi or plasma membrane
what are other forms of protein targeting other than co-translational translocation
post-translational translocation to to the mitochondria, nucleus, peroxisome, etc
difference between co- and post-translational translocation in the translation of transmembrane/integral membrane proteins
mRNA formed on free cytosolic ribosome
co- the ribosome binds to the rER membrane via translocator, mRNA is made directly into the rER.
post- the ribosomes finishes making the polypeptide chain which binds to chaperones, chain is then inserted into the rER
key characteristics of translocator
“side exit door” that inserts transmembrane domain of the polypeptide chain into the bilayer
ribsome-translocator binding is transient
Sec61
rER translocator protein complex
in co-translational translocation where does protein synthesis begin
free ribosomes
(except in mitochondria)
rER overview
Continuous with outer membrane of nuclear envelope
Lipid synthesis
Calcium storage in lumen
Detoxification reactions Transitional ER (regions without ribosomes form Cop II coated vesicles)
rER bound ribosomes
“gateway to secretory pathway”
rER ribosomes are transient and recruited from cytoplasmic ribosomes
rER ribosomes translate secretory and transmembrane proteins
rER lumen is TOPOLOGICALLY EQUIVALENT to outside of cell
what is the signal hypothesis
Free polyribosomes translate mRNA > N-terminal signal made > targets ribosome to rER > Signal directs chain to translocator in rER membrane > Signal CLEAVED in rER lumen to become mature polypeptide chain > chain folds into proper protein in rER lumen
sorting signal overview
directs polypeptide translation to rER
no consensus tho similar seq
has a central variable hydrophobic region
on N terminal in secretory proteins, REMOVED after entering ER lumen
TM segments can do the same in TM proteins, signal is NOT REMOVED
what are rough microsomes
rER membrane vesicles
used to study rER in lab
often come from pancreas
