2-protein trafficking Flashcards
Eukaryotic cells are highly organized with ____________
specialized sub-compartments
different organelles have _______
distinct ionic and pH compositions
cellular anatomy is _______
highly dynamic
protein traffic is required to _________
establish and maintain compartmental identity
where are proteins produced
ribosomes
proteins contain:
recognition motifs
examples of diverse recognition motifs:
- signal sequence
- signal patch
- post translational modification
recognition motifs are recognized by _____ which ______
machinery
facilitates transport to the appropriate organelle
what is the default pathway
cytosol
3 major mechanisms for protein targeting to organelles
- gated transport
- transmembrane transport
- vesicular transport
in nuclear/gated transport, what gets imported into the nucleus?
-all histones needed to make nucleosomes
-all ribosomal proteins needed for the association of rRNA
-all gene transcription factors
-all splicing factors needed to process pre-mRNA into mature mRNA molecules
in nuclear/gated transport, what gets exported from the nucleus?
-all ribosomal subunits containing both rRNA and proteins
-mRNA molecules
-tRNA molecules
-transcription factors that are returned to the cytosol to await reuse
what is gated transport?
-protein traffic between cytosol and nucleus through nuclear pore complexes.
-pore complexes function as selective gates that actively transport selected macromolecules
what is transmembrane transport?
-protein translocators directly transport proteins across a membrane from the cytosol into a space that is distinct.
-Transported in unfolded state
What is vesicular transport?
-membrane enclosed transport vesicles transport proteins from one compartment to another.
signals for nuclear/gated transport?
-nuclear localization signals (NLS)
-nuclear export signals (NES)
what are nuclear export signals (NES)
import proteins out of the nucleus via exportins
are nuclear localization signals cleaved after usage?
no, they remain in the cell in case the cell divides
how is nuclear transport regulated?
transcriptional control
what are nuclear localization signals (NLS)
import proteins into nucleus via importins
how do nuclear import/export signals work?
-NLS/NES signals are recognized by import/export receptors, proteins that act as taxis.
-Import/export receptors may interact with the cargo directly or indirectly.
many compartments are bounded by membranes composed of _______
lipid bilayers
in transmembrane protein transport, transport to organelles like ER/mitochondria crosses
lipid bilayer barriers
basic concept or vesicular transport
-all vesicle transfer processes involves budding and fusion
-cargo is contained within a transport vesicle
-fusion is regulated and specific
2 pathways of vesicular transport
-exocytic pathway
-endocytic pathway
example of exocytic pathway
site of protein synthesis in ER through Golgi to the plasma membrane
example of endocytic pathway
from plasma membrane through endosomes to lysosomes
what do transport vesicles do?
-carry material between compartments of the exocytic and endocytic pathway
all newly synthesized proteins destined for secretion from the cell or for organelles in the exocytic/endocytic pathways share a common entry point______
at the ER membrane
the signal for protein translocation across the ER membrane is
signal sequence
as translation occurs, the signal sequence is recognized by ___
SRP (signal recognition particle)
how do proteins enter ER?
- SRP recognized signal sequence in cytosol and binds to it
-brings the ribosome and nascent protein to the surface of ER membrane
-translocator imports the protein as it is synthesized across the ER membrane
-signal sequence is removed after translocation via signal peptidase
what happens to proteins in the ER
bind to core N-linked glycosylation that work as chaperones to facilitate correct protein binding
how is protein trafficking regulated
only correctly folded proteins are allowed to enter transport vesicles
what happens to proteins after it enters the ER?
-proteins are transported in vesicles to the Golgi
-further processes and sorted for transport
-endocytic vesicles are derived from plasma membrane
-endocytic vesicles traffic to endosomes where proteins can be recycled or transported
what are the different golgi processing fates?
-N linked oligosaccharides on proteins destined for plasma membrane are modified to terminate with sialic acid residues
-Diff post translational modifications create signals for diverse destinations
-N linked oligosaccharides destined for lysosome are modified by becoming phosphorylated on a mannose residue
a donor of vesicular transport
buds membrane bound transport vesicles that carry cargo
an acceptor of vesicular transport
receives cargo by fusion of incoming membrane-bound transport vesicles carrying cargo
what is M6P signal?
every protein that enters the lysosome must be tagged with M6P to enter
M6P groups are recognized by what?
transmembrane M6P receptor proteins which are present in Golgi
how does the protein go from the golgi to the lysosome?
- M6P groups are recognized by transmembrane M6P receptor proteins
- Receptor proteins bind to lysosomal hydrolases which help pack the hydrolases into clathrin coated vesicles that bud from golgi
- vesicles deliver contents to a late endosome and onto lysosome
in late endosomes, lysosomal hydrolases ______ from the M6P receptor
dissociate
M6P receptor protein binds M6P tag at the pH of the golgi network and releases it _____
at a slightly more acidic luminal pH of late endosomes
what is endocytosis
intracellular vesicle-mediated transport route that originates at the plasma membrane
what does endocytosis enable the cell to do?
-acquire nutrients including macromolecules, internalize receptors, and maintain cell surfaces
what are possible fates for transmembrane receptor proteins that have been endocytosed?
- returned to same plasma membrane (recycling)
- to a diff domain of the plasma membrane (transcytosis)
- follow the pathway to lysosomes (degredation)
