Trafficking Pathways Flashcards
Vesicular organs
ER, golgi, lysosomes, endosomes
Three domains of ER
Smooth-lipid metabolism
ROUGH-ribosomes
ERGIC- vesicles exit to golgi
Translation of free ribosomes in cytosol. Proteins go to
Cytosolic pathway.
Nucleus, peroxisomes, mitochondria, chloroplasts
Translation at membrane bound ribosomes
Secretory pathways. Golgi, plasma membrane, endosomes, lysosomes, nuclear membrane, secretory vesicles, peroxisome membrane
Cotranslational translocation
Proteins synthesized in membrane bound ribosomes enter ER during translation
SRP binds pausing translation, complex brings it to RER (SRP released), ribosome binds translocon and it opens, translation resumes and translocated across membrane
Post translational translocation
Proteins translated on free ribosomes move into ER after translation
Protein translated and HSP 70 and 40 maintain unfolded, bring to ER where recognized by Sec 62/63 and is inserted thru translocon, BiP drives protein inside and uses ATP for proper folding
What determines domain topology
Position of signal sequence
BiP
Chaperone, binds to unfolded polypeptide and mediates folding
Protein disulfide isomerase
Facilitates disulfide bind formation
N-linked glycosylation
Oligosaccharide (NAG and mannose) synthesized on lipid (dolichol) carrier and prevents protein aggregation in ER. Sorting signal
-modified in Golgi from just mannose and NAG to several different oligosaccharides (fucose, galactose, Sialic Acid)
GPI anchors
Glycolipids assembled in ER membrane added to C terminus. Lipidation
KDEL/KKXX
C terminus target sequence signals to go back to ER. Recognized in ERGIC. Ex: BiP
Golgi function
-proteins from ER are processed and sorted
-transport to endosomes, lysomes, plasma membrane, secretion
-synthesize glycolipids and sphingomyelin
4 regions
Stable cisternae model
Transport vesicles carry proteins between cisternae for protein movement in golgi
Cisternal maturation model
Proteins carried within cisternae which gradually mature and progressively move through golgi in cis to trans direction
N-linked oligosaccharides of lysosomal proteins
Modified by mannose phosphorylation using UDP. Recognized by mannose-6-phosphate receptor in trans golgi network, which transports them to endosomes then lysosomes
O linked glycosylation
Carbohydrates added to side chains of serine and threonine in golgi. Makes proteoglycans, can be further modified by addition of sulfate groups
3 ways transport form golgi to cell surface can occur
Direct transport to plasma membrane, recycling endosomes, regulated secretory pathways (granules)
Hormones and neurotransmitters
Aggregate in trans golgi network and are packaged into secretory granules until signals direct their fusion with plasma membrane
COPII coated vesicles
Carry proteins from ER to ERGIC and onto golgi
COPI coated vesicles
Bud from ERGIC or golgi and carry their cargo back to earlier compartments
Clatherin coated vesicles
Both directions between the trans golgi network, endosomes, lysosomes, plasma membrane
Formation of coated vesicles regulated by
Small GTP binding proteins (ARF1 and Sar1).
Uses GEF for GDP to GTP, adds adapter, cargo and coat
Interaction between transport vesicles and target membranes mediated by
Tethering factors and small GTP binding proteins (Rab)
