Vesicle Trafficking Flashcards
match the disease with the defective cell structure:
Zellweger syndrome, I-cell disease, hypercholesterolemia
lysosomes, endosomes, peroxisome
Zellweger syndrome: defective peroxisome (due to lack of transport of enzyme proteins into peroxisome)
I-cell disease: defects lysosome (I = lysosome)
hypercholesterolemia: defective endocytosis (endosomes)
protein transfer to all organelles except ____ is post-translational
ER
mediated by organelle specific signal sequences
monomeric GTP binding proteins participate in many events in intracelular trafficking - what are the enzymes involved?
GEF (guanine-nucleotide exchange protein) releases GDP to allow GTP to bind —> active state
GAP (GTPase) hydrolyzes GTP —> inactive state
nuclear localization sequence (NLS) binds cytoplasmic protein ____, which brings nuclear proteins to/through nuclear pore
importin
separates from nuclear proteins once in nucleus
GTP binding protein used in release of nuclear proteins from receptor used for nuclear import:
Ran GTPase - releases nuclear proteins from importin complex in the nucleus
what causes Zellweger syndrome
defect in recognition signal of peroxisomal enzyme proteins - do not get delivered to peroxisome, so peroxisome is defective
secretory proteins start translation in cytoplasm but are halted and transferred to RER. how does this happen?
need 2 things: SRP and GTP hydrolysis
N-termini of secretory pathway proteins have signal sequence that binds Signal Recognition Particle (SRP), which stops synthesis and brings ribosome to RER
GTP hydrolysis occur on both SRP and SRP receptor before protein is released and synthesis continues
this is how RER becomes “studded” with ribosomes
what are the steps of protein processing as protein synthesis continues on ER membrane (after delivery from cytoplasm)?
- signal peptide removed
- disulfide bonds form
- chaperones aid in folding - NO export from ER unless properly folded (misfolded go to proteosome)
- glycosylation (on lumen side) - critical for ER exit
how do vesicles for transport “find destination”
complementary SNARES on vesicle and target (very specific - allow vesicle and target to “snare” each other)
Rab GTPases - GTP binding proteins allow vesicles to initially locate target and check specificity
match protein coat with transport event
clathrin, coatamer I, coatamer II
ER to cis-Golgi, retrograde, cell surface to early endosome
clathrin: cell surface to early endosome, receptor mediated endocytosis
COP II: ER to cis-Golgi
COP I: retrograde
match GTP binding protein with function
Ran GTPase, Arf and Sar-1, Rab GTPase
release of nuclear proteins, formation of transport vesicles, recognition of transport vesicles by target organelles
Ran GTPase: release of nuclear proteins
Arf, Sar-1: formation of transport vesicles
Rab GTPase: recognition of transport vesicles by target organelle
what GTP binding protein regulates COP-II vesicles (ER to cis-golgi)
Sar-1
[Arf is for COP-I]
botulinum and tetanus toxins affect vesicular transport by cleaving _____
v-SNARES, preventing vesicular fusion and NT release
complementary v and t SNARES mediated vesicle-target recognition and fusion, function as lock and key (via coiled-coil winding)
[v = vesicle, t = target]
complete this description of transport of lysosomal enzymes to lysosomes:
1. lysosomal proteins are marked by addition of ____ to ____ sugar residue in cis-Golgi
2. ____ receptors in trans-golgi network (TGN) recognize the modification
3. lysosomal enzymes packaged into ___ coated vesicles
4. transported to late endosome and then to lysosome
- lysosomal proteins are marked by addition of PHOSPHATE to MANNOSE sugar residue in cis-Golgi
- M-6-P receptors in trans-golgi network (TGN) recognize the modification
- lysosomal enzymes packaged into CLATHRIN coated vesicles
- transported to late endosome and then to lysosome
- ligand-receptor dissociates at acidic pH of lysosome
what is the cause and effect of Inclusion (I-cell) disease in humans?
mannose-6 residue is not phosphorylated on lysosomal proteins (phosphotransferase mutation)
all lysosomal enzymes are secreted because they cannot be recognized by M-6-P receptor in trans-Golgi, so are not directed towards lysosome
what happens to cell function during Legionairre’s disease?
bacteria is engulfed in phagosome, but hijacks host vesicles to block delivery to lysosome
isn’t degraded and replicates instead
cargo of receptor-mediated endocytosis can be diverted from lysosome to basolateral membrane via ____
transcytosis - allows bypass of tight junctions
import for delivering antibodies to neonates
contrast cargo trafficking following receptor-mediated endocytosis of cholesterol and EGF (epidermal growth factor)
LDL carries cholesterol as lipoprotein complex, fuses with endosome then is recycled back to surface
EGF receptor is not recycled but delivered to lysosome for receptor down-regulation
function of adaptins in endocytosis
adaptins bind clathrin (coat) and receptors for extracellular cargo
needed to “adapt” cargo into vesicle
how does a mutation in LDL receptor tail prevent cholesterol clearance and cause hypercholesterolemia?
interferes with receptor binding to adaptin
so even if cargo is bound to receptor it cannot be incorporated into vesicles
which is true of peroxisomes:
a. have enzymes that are normally exported from the cell
b. require organelle-specific cell surface receptors to import peroxisome-specific proteins
c. contain proteins that have traveled through the Golgi complex
b. require organelle-specific cell surface receptors to import peroxisome-specific proteins
peroxisomal proteins complete synthesis in cytoplasm - do not enter Golgi or secretory vesicles
what’s wrong with this sentence?
vesicular transport uses GTP binding proteins that mediate the conversion of GDP to GTP
GTPases mediate conversion, NOT GTP binding proteins (Gbp)
do you need vesicles for nuclear transport?
NO
vesicular transport uses one set of specific ____ to deliver cargo to the trans-golgi network (TGN)
v-SNARES and t-SNARES
why are lysosomal enzymes glycosylated?
needed for identification by receptor (phosphate is added to mannose)
