Chapter 13: Intracellular Membrane Traffic Flashcards
What important concept is maintained during intracellular membrane trafficking?
topological equivalence
What are the 3 types of intracellular membrane trafficking pathways?
- endocytic
- biosynthetic-secretory
- retrieval
What pathway involves absorbing extracellular material into the cell?
endocytic pathway
what pathway involves the transfer of material from the nuclear envelope/ER to the Golgi, vesicles, or outside of the cell?
Biosynthetic-secretory pathway
what pathway involves the transfer of cell material from other pathways back to the ER?
retrieval pathway
The endocytic pathway utilizes what protein to aid in intracellular transport?
clathrin
Retrograde transport utilizes what protein to aid in intracellular transport?
COP1
The synthesis and secretory transport utilize what protein to aid in intracellular transport?
COP2 (+clathrin)
Cholesterol receptor-mediated endocytosis is typically regulated by what protein/transport type?
Clathrin; endocytic pathway
In what scenario would a cell use COP1 proteins for intracellular membrane transport?
To return proteins that have been mistakenly transported to certain organelles; retrieval/retrograde pathway
COP2 proteins are found in what portion of the cell? What is their function?
ER; transport to topologically equivalent spaces
What are the 4 basic steps of clathrin-based vesicle formation?
- coat assembly and cargo selection
- bud formation
- vesicle formation
- uncoating
This particular protein attaches to cargo receptors to allow for the association of the clathrin triskeleton
adaptor protein
these proteins aid in the vesicular formation of a clathrin-coated membrane
membrane-bending and fissure proteins
On what side of the membrane does the clathrin triskeleton bind to?
cytosolic
What phenomenon induces the budding and fission of a clathrin-coated vesicle?
clathrin triskeleton bending
This is a vesicular formation/fission protein that has contractile function driven by GTP
dynamin helix
What are the three steps of directed traffic endocytosis?
- tethering of vesicle via Rab-GTP
- docking on membrane via t-snare/v-snare interaction
- Fusion of vesicle into cell (and release of Rab-GTP)
What is required of a protein for COP2 ER transport of it to occur?
exit signal corresponding to cargo receptor
What are the 2 possible fates of a resident ER protein?
- retention signal prevents removal – remains in ER lumen
- protein is taken up by vesicle formation – diffused out of ER lumen (to topologically equivalent spaces)
These are membrane-bound regions between the ER and cis-Golgi network where retrieval transport can occur
vesicular tubular cluster
What are the 3 cisternae of the Golgi stack?
- cis
- medial
- trans
What are the 3 total regions of the Golgi apparatus?
- cis Golgi network
- Golgi stack
- trans Golgi network (TGN)
The cis Golgi network is responsible for what?
Sorting & phosphorylation of oligosaccarides
The cis cisternae of the Golgi stack is responsible for what?
removal of Man
what is the function of the medial cisterna of the Golgi stack?
removal of Man & addition of GlcNAc
what is the function of the trans cisterna of the Golgi stack?
addition of Gal & addition of NANA
what is the function of the trans cisterna of the Golgi stack?
addition of Gal & addition of NANA
what is the function of the TGN?
sorting & sulfation of tyrosines and carbohydrates
what are the 3 major fates of TGN sorting?
- lysosome
- plasma membrane
- secretory vesicle
what are the three possible sources of a lysosome?
- phagosome
- late endosome
- autophagosome
this vesicular structure is responsible for digesting the cell’s own structures (i.e. mitochondrion, chloroplasts)
autophagosome
this vesicular structure is formed via the endocytosis of large, foreign structures (i.e. bacterium)
phagosome
this vesicular structure is formed via the endocytosis of smaller structures and can mature into another structure when introduced to a product of macropinocytosis
early endosome
the addition of the products of macropinocytosis to the products of endocytosis results in what structure?
late endosome
What are the 7 basic steps (and the locations where they occur) of lysosomal hydrolase transport to endosomes?
- Addition of P-GlcNAc (cis Golgi network)
- uncover M6P signal (Golgi stack)
- Binding to M6P receptor (TGN)
- Transport to endosome (transport vesicle)
- Dissociation @ acidic pH (endosome)
- Removal of phosphate (endosome)
- Receptor retrieval (transport vesicle)
What is essential in providing the acidic endosomal environment to ensure the dissociation of lysosomal hydrolase precursor from the M6P receptor?
V-type ATP proton pump
Where is the dysfunction located at in I-cell disease?
lack of M6P signal (no mannose phosphorylation) on lysosomal hydrolase precursor
What is the result of I-cell disease?
insufficient endosomal hydrolase activity–largely effects nervous system
What are the 8 basic steps of cholesterol delivery via LDLs?
- LDL binding to extracellular receptors
- formation of clathrin coat
- uncoating
- fusion into Golgi network
- LDL transfer to late endosome (& retrieval of LDL receptor)
- late endosome –> endolysosome
- release of free cholesterol via hydrolytic enzymes
- recycling of lysosome
this secretory pathway is used to transport/release membrane lipids or soluble proteins in an unregulated membrane fusion; this is often the default for molecules with no target info
constitutive secretory pathway
this secretory pathway occurs in response to the activity of an extracellular receptor (via hormones/NTMs) to induce regulated membrane fusion
regulated secretory pathway
In what cells to secretory vesicles form?
only in cells that perform excretion functions (i.e. toxicant removal)
What is the default fate/location of a protein translocated into the ER lumen (only contains an ER localizing signal)?
extracellular space
What is the default fate/location of proteins synthesized via cytosolic transcription?
usually mitochondria/chloroplast–otherwise they remain in cytosol
