Vesicle Trafficking

Question 1

match the disease with the defective cell structure:
Zellweger syndrome, I-cell disease, hypercholesterolemia

lysosomes, endosomes, peroxisome

Answer 1

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)

Question 2

protein transfer to all organelles except ____ is post-translational

Answer 2

ER

mediated by organelle specific signal sequences

Question 3

monomeric GTP binding proteins participate in many events in intracelular trafficking - what are the enzymes involved?

Answer 3

GEF (guanine-nucleotide exchange protein) releases GDP to allow GTP to bind —> active state

GAP (GTPase) hydrolyzes GTP —> inactive state

Question 4

nuclear localization sequence (NLS) binds cytoplasmic protein ____, which brings nuclear proteins to/through nuclear pore

Answer 4

importin

separates from nuclear proteins once in nucleus

Question 5

GTP binding protein used in release of nuclear proteins from receptor used for nuclear import:

Answer 5

Ran GTPase - releases nuclear proteins from importin complex in the nucleus

Question 6

what causes Zellweger syndrome

Answer 6

defect in recognition signal of peroxisomal enzyme proteins - do not get delivered to peroxisome, so peroxisome is defective

Question 7

secretory proteins start translation in cytoplasm but are halted and transferred to RER. how does this happen?

Answer 7

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

Question 8

what are the steps of protein processing as protein synthesis continues on ER membrane (after delivery from cytoplasm)?

Answer 8

1. signal peptide removed
2. disulfide bonds form
3. chaperones aid in folding - NO export from ER unless properly folded (misfolded go to proteosome)
4. glycosylation (on lumen side) - critical for ER exit

Question 9

how do vesicles for transport “find destination”

Answer 9

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

Question 10

match protein coat with transport event
clathrin, coatamer I, coatamer II

ER to cis-Golgi, retrograde, cell surface to early endosome

Answer 10

clathrin: cell surface to early endosome, receptor mediated endocytosis

COP II: ER to cis-Golgi

COP I: retrograde

Question 11

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

Answer 11

Ran GTPase: release of nuclear proteins

Arf, Sar-1: formation of transport vesicles

Rab GTPase: recognition of transport vesicles by target organelle

Question 12

what GTP binding protein regulates COP-II vesicles (ER to cis-golgi)

Answer 12

Sar-1

[Arf is for COP-I]

Question 13

botulinum and tetanus toxins affect vesicular transport by cleaving _____

Answer 13

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]

Question 14

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

Answer 14

1. lysosomal proteins are marked by addition of PHOSPHATE to MANNOSE sugar residue in cis-Golgi
2. M-6-P receptors in trans-golgi network (TGN) recognize the modification
3. lysosomal enzymes packaged into CLATHRIN coated vesicles
4. transported to late endosome and then to lysosome
5. ligand-receptor dissociates at acidic pH of lysosome

Question 15

what is the cause and effect of Inclusion (I-cell) disease in humans?

Answer 15

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

Question 16

what happens to cell function during Legionairre’s disease?

Answer 16

bacteria is engulfed in phagosome, but hijacks host vesicles to block delivery to lysosome

isn’t degraded and replicates instead

Question 17

cargo of receptor-mediated endocytosis can be diverted from lysosome to basolateral membrane via ____

Answer 17

transcytosis - allows bypass of tight junctions

import for delivering antibodies to neonates

Question 18

contrast cargo trafficking following receptor-mediated endocytosis of cholesterol and EGF (epidermal growth factor)

Answer 18

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

Question 19

function of adaptins in endocytosis

Answer 19

adaptins bind clathrin (coat) and receptors for extracellular cargo

needed to “adapt” cargo into vesicle

Question 20

how does a mutation in LDL receptor tail prevent cholesterol clearance and cause hypercholesterolemia?

Answer 20

interferes with receptor binding to adaptin

so even if cargo is bound to receptor it cannot be incorporated into vesicles

Question 21

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

Answer 21

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

Question 22

what’s wrong with this sentence?

vesicular transport uses GTP binding proteins that mediate the conversion of GDP to GTP

Answer 22

GTPases mediate conversion, NOT GTP binding proteins (Gbp)

Question 23

do you need vesicles for nuclear transport?

Answer 23

NO

Question 24

vesicular transport uses one set of specific ____ to deliver cargo to the trans-golgi network (TGN)

Answer 24

v-SNARES and t-SNARES

Question 25

why are lysosomal enzymes glycosylated?

Answer 25

needed for identification by receptor (phosphate is added to mannose)