1.9 Protein Trafficking & Targeting Flashcards
Proteins to be translocated contain _____ that help direct them to their proper location. What are these structures composed of?
tags
specific amino acid sequences
______ bind the tag sequence and direct the protein to their destination
chaperone
additional proteins form _____ (______) to allow translocation of proteins into membrane bound organelles
pores (translocon)
how many tags can a protein have?
multiple if need to go multiple locations
where does all protein translation begin?
cytosol (except for 13 mitochondrial proteins)
if all protein translation begins in the cytosol, do they end there as well?
no
what structures does the secretory pathway consist of? what is system called?
ER, Golgi apparatus, lysosomes, endosomes, and secretory vesicles
endomembrane system
what is the function of secretory pathway?
processing of proteins for export from the cell, proteins destined for the plasma membrane, lysosomes, vacuoles, etc
what is the first step for proteins entering the secretory pathway?
target the ER
what is the next step in secretory pathway after proteins enter the ER?
carried by vesicle transport to other compartments of system. highly regulated
in secretory pathway, the proteins targeted to the ER require a ______ or ______
tag or targeting signal (signal sequence or signal peptide)
the tag, or targeting signal required by proteins to be sent to ER is encoded within where?
the N-terminal portion of the protein
the tag, or targeting signal required by proteins to be sent to ER is encoded within where?
the N-terminal portion of the protein
proteins that do not have a signal peptide stay where for the rest of translation?
in the cytosol
the signal sequence for proteins targeted to ER in secretory pathway, is recognized by what?
signal recognition particle (SRP)
what does the SRP do?
in the secretory pathway, is directs the ribosome to a specific receptor on the ER. this signal sequence also prevents the ribosome from continuing translation in the cytosol.
what removes the signal sequence on the protein after it is successfully moved into the ER? what does this allow the protein to do?
signal peptidase
it releases the peptide which folds into its correct shape
what enzyme adds sugars to protein during translation
glycosyltransferase
what are the first to events that occur when proteins get moved to the ER lumen?
- signal peptidase removes signal sequence
2. gylcosyltransferase adds sugars during translation
proteins destined to remain in ER membrane have an amino acid tag that determines this location called _____
stop transfer sequence (STA)
explain the structure, function, and process of STA in the ER membrane?
22-25 hydrophobic amino acid sequence in the middle of the protein that forms an alpha helix
when encountered it gets moved into the membrane, then translation of the rest of the protein continues in cytosol
what things are required in order to assist proper protein folding and release from the ER?
- molecular chaperones
2. folding enzymes
what types of bonds are formed and rearranged in the ER?
Disulfide bonds
what happens to terminally misfolded proteins in the ER?
they are degraded in the cytosol
