Vesicular Transport Flashcards
1
Q
transportation of proteins and other biomolecules
A
vesicular transport
2
Q
cargo
A
the contents of vesicles
3
Q
vesicular transport is _____ .
A
directional
4
Q
vesicular transport
A
a continuous exchange of components between various membrane bound compartments
5
Q
cues for incoming traffic
A
- composition of memb.
2. molecular markers on memb. surface
6
Q
molecular address
A
combination of molecular markers
7
Q
return of molecules to the source
A
retrieval pathway
8
Q
how does a cell segregate proteins
A
cells segregate proteins into membrane domains by assembling a cytosolic coat
9
Q
2 major functions of vesicle coats
A
- pulls specific proteins into a specialized patch
2. molds the vesicle into a basket like structure
10
Q
loss of coat
A
coat is discarded after the vesicle has budded off and before it fuses with target
11
Q
list the types of coats
A
- clathrin
- COPI
- COPII
12
Q
clathrin direction
A
mediate transport from golgi and from plasma membrane
13
Q
major protein in clathrin coated vesicles
A
clathrin
14
Q
clathrin structure
A
- each subunit has 3 small and 3 large polypeptide chains
- which for a 3 - legged structure
15
Q
what is the structure of clathrin called?
A
triskelion
16
Q
overall clathrin structure
A
assembled into basket shapes
- hexagon/pentagon forming the basket
- form coated pits on cytosolic side
17
Q
second layer between cage and membrane
A
cage = coat
adaptor proteins
18
Q
role of transmembrane proteins in clathrin coated vesicles
A
- receptors that bind to cargo inside
- allows cargo to be trapped within vesicle
- adaptor proteins bind on outside
19
Q
assembly of clathrin vesicles
A
- initial grouping of clathrin on adaptor proteins induces a curvature into membrane
- first step in budding off
- each clathrin protein binds to a adaptor protein to create a full circle
20
Q
assembly of clathrin vesicles: adaptor proteins
A
- bind to transmembrane proteins that are bound to cargo interiorly
- bind to clathrin proteins
- allow for selective recruitment of cargo and coating molecules
21
Q
dynamin is involved in _____ of clathrin coats.
A
budding off —- which ultimately causes the clathrin coat to disassemble
22
Q
pinching
A
bringing of 2 cytosolic sides together to allow fusion and release of bud as a vesicle
23
Q
function of dynamin
A
- assembles ring around neck of a budding off vesicle
2. squeezes and cuts the bud off
24
Q
dynamin domains
A
- PIP2 binding domain – tethers protein to membrane
2. GTPase domain – regulates rate of pinch off
25
dynamin also recruits other ….. ?
other proteins to distort the lipid bilayer via lipid modifying enzymes that change the lipid composition
26
vesicle loses coat
PIP2 is degraded after budding off
| - results in weakening of binding of coat to adapter proteins
27
role of HSP70 in clathrin coats
uses ATP to peel off the clathrin coat after PIP2 has become degraded (which occurs after budding)
28
COPI
- mediates transport from golgi cisternae
| - important in retrieval pathway
29
COPII
- mediates transport from ER
30
plays a major role in coat assembly, vesicle formation and protein trafficking
phosphoinositide
31
functions of phosphoinositide
1. mark organelles/membrane domains for target
2. control recruitment/binding of specific proteins per specific destination
3. regulate vesicle trafficking
32
de-phos/phosphorylation of phosphoinositide
- occurs at 3,4,5' positions
- form various derivatives
- each has their own unique actions
- can interconvert between derivates
33
interconversions between phosphoinositides
- highly compartmentalized
- specific to organelle or domain
- facilitated by PI kinases and phosphates ---- different organelles have unique sets of these
34
____ binds with high _____ to the ____ groups of phosphoinositides.
protein
specificity
head groups
35
membrane bending proteins
BAR domains
36
BAR domain structure
- coiled coils
| - + charge towards inner surface which is in contact with the (-) charged membrane
37
BAR domain function
- their + charge interacts with (-) memb.
| - causes memb. to bend/bow outward
38
Rab and SNAREs are involved in ______ .
vesicle targeting
39
list the 2 important factors involved in vesicle targeting
1. Rab
| 2. SNAREs
40
role of rab
direct vesicles to specific domains on target membrane
~60 types
monomeric GTPase
41
forms of rab
1. inactive-cytosolic-GDP
| 2. active-membrane bound-GTP
42
inactive rab
1. GDP form
2. kept inactive by the binding of GDI
3. this form is soluble
43
GDI
GDP dissociation inhibitor
44
active rab
1. GTP form
2. Rab-GEF keeps it in active form
3. tightly bound to a memb.
4. binds to rab effectors present on target memb.
45
rab effectors
- present on target memb.
- motor/tethering proteins
- facilitate memb. tethering and fusion of vesicle
46
list the types of Rabs for exam
1. Rab1
2. Rab3A
3. Rab5
47
rab1
ER and golgi complex
48
rab3a
synaptic vesicles
| secretory vesicles
49
rab5
early endosomes
plasma memb.
clathrin-coated vesicles
50
role of SNARE proteins
- mediate fusion of vesicle with memb.
- 35 different types
- exist as complimentary pairs
51
forms of SNARE
1. v-snare
| 2. t-snare
52
v-snare
vesicular snare
- single polypeptide
- found on vesicle memb.
53
t-snare
target snare
- 2-3 proteins
- found on target membrane location
54
snare mechanism
1. v and t interact
2. wrap tightly around each other
3. expels any cytosol in between
4. bringing memb. into contact
5. resulting in fusion of vesicle and intertwined snares left on outer membrane
55
triggering of fusion
may be triggered by extracellular signals which remove inhibitory proteins which were preventing fusion
56
dissociated of snare pairs
accessory protein + NSF + ATP = untangling of snares
both snares are still anchored in membrane
v-snare will become part of a new vesicle once one buds off in that location
57
protein options w/in ER
1. they are an ER protein and stay in lumen
2. contain an exit signal for a specific location
3. misfolded/damaged = degraded and retained w/in ER
58
newly ER synthesized proteins are packaged into ____ coated vesicles and then ?
COPII
| -bud off from ER exit sites
59
exit signals
- displayed by proteins on cytosolic surface
| - recognized by receptors present on COPII coat
60
fate of damaged/misfolded proteins in ER lumen
chaperones bind to them and degrade them for recycling
61
ER lumen chaperones
BiP and calnexin
| for damaged proteins
62
vesicular tubular _____ .
clusters
| -vesicles can fuse together after shedding their coat to form larger structures
63
fusion of several vesicles requires ____ .
snares
| both v and t types
64
types of vesicle clusters
1. homotypic - same cargo/same origin
| 2. heterotypic - dif. cargo/dif. origin
65
properties of vesicular tubular clusters
- short lived
- move along microtubules to golgi via motor proteins
- fuse w/ golgi to deliver contents
66
vesicles budding off golgi to get to ER are coated with ____ ?
COPI
67
ER retrieval signals
1. kkxx
| 2. kdel
68
ER retrieval signal present in ER membrane proteins
- kkxx
- signal interacts w/ COPI vesicles
- gets packaged in w/ COPI vesicles and signals golgi that it shouldn't be there
- does not require receptors
69
ER retrieval signal present in _____ proteins at the ___ terminus .
- kdel, soluble proteins, C terminal
- requires kdel receptor which helps them package w/in COPI vesicles
- it is an actual sequence on the physical protein --- tells golgi it should not be there
70
cisternae
golgi is a collection of flattened membrane enclosed compartments called cisternae
71
faces of the golgi complex
1. cis or entry --- faces ER
| 2. trans or exit --- faces plasma memb.
72
CGN
- cis golgi network
- network of fused vesicular tubular cluster from ER
- proteins/lipids enter golgi from CGN
73
TGN
- trans golgi network
- regions that allow exit of proteins/lipids
- next step of secretory pathway
74
golgi also plays an important role in _____ .
protein glycosylation
75
golgi hypotheses
1. cisternal maturation model
2. vesicle transport model
research supports both models --- describe how the golgi maintains it's dynamic shape
76
lysosomes
membrane enclosed compartments filled with 40 types of enzymes important for intracellular digestion
derived from late endosomes
77
what are the lysosome enzymes collectively referred to as?
hydrolases
78
2 things lysosomes require
1. acidic internal environment
| 2. proteolytic cleavage for activation
79
vacuolar ATPase
- on lysosomal membrane
| - pumps H+ inside to maintain low pH and to drive transport of small metabolites
80
what happens post digestion?
-lysosome pumps end products out into cytosol for recycling
81
list steps of lysosome maturation
1. early endosome
2. late endosome
3. endolysosome
4. lysosome
82
autophagy
- -when an organelle is damaged or old and needs to be rid off
- -cell delivers to lysosome for breakdown
83
model of autophagy
1. induction
2. closure-autophagosome
3. fusion - w/ lysosome
4. digestion
5. return to normal lysosome state
84
describe induction phase of autophagy
cell forms a bunch of little vesicles containing engulfed cytosol
join together to form a large compartment
85
describe closure phase of autophagy
the large form of joined compartments circle completely around the damaged material
- now termed autophagosome
- has double membrane
86
transport from TGN to ….
pathway that delivers membrane proteins and hydrolases to lysosomes
- -buds off TGN = endosomes
- -can develop into lysosomes
87
sorting signal for lysosomal proteins
mannose-6-phosphate (sugar signal)
M6P
is attached to proteins in the CGN
88
proteins after budding off from TGN
- -the acidic environment causes receptor proteins to release their proteins and sugar signal is removed
- -receptor proteins bud off and return to golgi to be recycled
89
protein-M6P budding off from TGN
M6P signal binds to specific receptors, clathrin coat forms and vesicle buds off, loses coat
now an endosome
90
addition of signal to lysosomal hydrolase
1. mannose is added to N-linked oligosaccharide w/ mannose as terminal residue
2. UDP-GInNAc binds to phosphotransferase
3. enzyme binds to GIcNAc phosphotransferase
4. GIcNAc-Pi transferred to mannose in catalytic site
5. protein-oligosaccharide-mannose-GIcNAc-Pi released
6. GIcNAc is removed
7. now have lysosomal hydrolase w/ M6P sugar signal
91
what results if defects exist in lysosomal hydrolases?
accumulation of undigested material in the lysosome
92
hurler's disease
mutation in the enzyme required to break down GAGs
93
inclusion cell disease
1. all lysosomal hydrolases are missing
| 2. undigested material accumulates = inclusions
94
enzyme that adds M6P
GIcNAc--phosphotransferase
95
what happens if there is a defect in the enzyme responsible for adding M6P?
hydrolases are not phosphorylated and thus not sorted into vesicle and never delivered into lysosomes
instead carried to cell surface and secreted into blood
96
uptake of macromolecules from exterior
endocytosis
97
in endocytosis, material is progressively enclosed by a portion of the _____ .
plasma membrane
98
describe general endocytosis mechanism
1. PM invaginates
2. pinches off
3. which forms endocytic vesicles or endosome
99
large particles ingested by vesicles called ______
phagocytosis
phagosomes
a specialized form of endocytosis, only done by WBCs
100
small particles ingested by vesicles
pinocytosis
| or cell drinking
101
used to import select macromolecules from outside cell
receptor-mediated endocytosis
provides selective concentration
ex = cholesterol intake
102
describe receptor-mediated endocytosis
1. molecules bind to receptors on exterior PM
2. accumulate in clathrin coated pits
3. enters cell as = receptor-macromolecule complex w/in a clathrin coated vesicle
103
blockage of cholesterol intake pathway
atherosclerosis
104
fate of endocytosed receptor proteins
enveloped in transport vesicle = transcytosis
reinserted in PM to be used again
105
insulin binds to an insulin receptor, causing ….?
sends an intracellular signal to relocate glut transporters to be within the membrane instead of the interior glut pool
results in an increase in glucose intake
106
phagocytosis is carried out by?
phagocytes, WBCs such as macrophages and neutrophils
107
phagocytes are capable of ingesting
microorganisms
senescent cells
apoptotic cells
108
in order for phagocytes to digest their material ….
phagosomes fuse w/ lysosomes to degrade ingested material
109
undigested material can be secreted out via
exocytosis
110
phagocytosis is triggered by
binding of particles to receptors on phagocyte surface
antibodies bind to the microbe
Fc chain recognized by Fc receptor on phagocyte surface
111
binding of phagocytes to material triggers
formation of pseudopod
| which engulfs the particle to form a phagosome
112
pseudopod formation is driven by ?
local actin polymerization and reorganization to surround the material and engulf it
113
control of pseudopod formation
by Rho GTPases and phosphoinositide signaling
114
pinocytosis occurs _____ in all eukaryotic cells
continuously
115
pinocytosis process begins at _____
clathrin coated pits
PM invagination
pinch off
clathrin coated vesicle
116
what is trapped within vesicles via pinocytosis
extracellular fluid w/ various solutes trapped in pits
117
flask shaped invaginations in PM
caveolae
| rich w/ cholesterol and glycosphingolipids and GPI anchoring proteins
118
major structural protein of caveolae
caveolin
119
caveola invaginate into membrane by their unique _____ and not the _____.
lipid composition not the protein coat
120
______ pinches off caveolae from PM
dynamin
121
endosome-like compartment from caveolae
caveosome
| which do not connect with lysosomes
122
transport vesicles move from TGN to PM
exocytosis
123
in exocytosis, ______ and _____ in vesicles are destined for the _____
membrane proteins
lipids
PM
124
______ secretory pathway operates continuously : exocytosis
constitutive
125
_______ secretory pathway operates only when triggered by signals: exocytosis
regulated
126
examples of signals for exocytosis
hormones
| neurotransmitters
127
3 paths for protein sorting in TGN
1. M6P signal diversion to lysosomes via endosomes
2. constitutive secretory pathway of exocytosis
3. signal mediated diversion to secretory vesicles for regulated exocytosis secretion
128
steps of forming a secretory vesicle
1. accumulation of cargo in one spot of TGN
2. clathrin coated immature secretory vesicle buds off
3. clathrin coat lost
4. mature secretory vesicle
129
what happens to mature secretory vesicles before regulated exocytosis occurs
1. travel to PM
2. are held close to memb. by SNAREs
3. complexin blocks SNAREs from fusing the PM and vesicle
so vesicle is just help close to memb. ready for release but does not occur until signals such as action potentials cause their release
130
exocytosis SNAREs
1. v-SNARE = synaptobrevin
2. t-SNARE = syntaxin
3. t-SNARE = SNAP25
4. synaptotagmin
131
list the phases of synaptic vesicle exocytosis
1. docking
2. priming I
3. priming II
4. fusion fore opening
5. fusion complete
132
synaptobrevin
v-SNARE of exocytosis synaptic vesicles
133
syntaxin
t-SNARE of exocytosis synaptic vesicles
134
SNAP25
second t-SNARE of exocytosis synaptic vesicles
helps syntaxin bring the vesicle into contact w/ PM by coiling w/ synaptobrevin
135
synaptotagmin
a v-SNARE with Ca binding sites
when an action potential occurs Ca binds and synaptotagmin counteracts complexin
allowing the other SNAREs to bring vesicles into PM for fusion
136
complexin
responsible for blocking synaptic vesicle fusion w/ presynaptic membrane until an action potential occurs
synaptotagmin stops complexin to allow fusion
