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MBB 231 > Lecture 13 - Endomembranes & Vesicles > Flashcards

Lecture 13 - Endomembranes & Vesicles Flashcards

1
Q

what are the functions of vesicles protein coatings?

A
  1. curve the membrane to form the vesicle
  2. select the components to be carried in the vesicle
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2
Q

def: vesicle coating, acts as a scaffolding cage around the vesicle

A

outer layer

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3
Q

def: vesicle coating, acts as an adaptor between the outer layer and the lipid bilayer/cargo

A

inner layer

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4
Q

def: move materials from the ER “forward” to the ERGIC and Golgi complex

A

COPII coated vesicles

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5
Q

def: move materials from the ERGIC and Golgi “backward” to ER or from the trans Golgi to the cis Golgi cisternae

A

COPI coated vesicles

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6
Q

def: move materials from the plasma membrane “backwards”, and the TGN to the endoscopes/lysosomes/plant vacuoles

A

Clathrin-coated vesicles

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7
Q

in a COPII coated vesicle, what is budding initiated by?

A

the recruitment of small GGTP binding proteins (GTPases) = SAR1-GDP to a patch of donor membrane

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8
Q

what gives COPII vesicles their curvature?

A

Sec23 and Sec24 dimers, since they have curved conformation

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9
Q

def: not only curving protein, but also acts as an adaptor protein, associating with ER export signals recruiting proteins to the forming vesicle

A

Sec24

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10
Q

def: integral membrane protein crucial for the fusion of the vesicle to the correct target membrane

A

v-SNAREs

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11
Q

in COPII what forms the cage like outer layer?

A

Sec13 and Sec 31

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12
Q

for COPII vesicles, the outer layer is a relatively simple _____, with each vertex forming from the convergence of ____ ______ ____ dimers

A

lattice, four Sec13 and Sec31 dimers

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13
Q

what happens to the protein coat while in transit of COPII and why

A

it disassembles and release its contents back into the cytosol so the v-SNAREs are accessible and the vesicle can target the proper membrane

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14
Q

what chemical process mediates the disassembly of the protein coat of the vesicle?

A

hydrolysis of GTP, producing SAR1-GDP

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15
Q

what mediates the movement of vesicles while reaching their targets?

A

microtubules

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16
Q

the initial contact between a vesicle and the target membrane involves _________ proteins

A

tethering

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17
Q

what are the 2 groups of tethers?

A
  1. rod shaped fibrous proteins that form long bridges
  2. multi-protein complexes that hold two membranes close together
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18
Q

def: regulates membrane specificity and is responsible for most of membrane vesicle/target specificity, group of GTPases

A

Rab GTPases

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19
Q

how does Rab-GTP allow docking to occur?

A
  • recruits the cytosolic tether proteins to the membrane surface
  • recruits motor proteins to the vesicle to facilitate transport
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20
Q

SNARE proteins _____ _______ between vesicles and target membranes

A

mediate fusions

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21
Q

def: sorting and targeting of vesicles involves two families of SNARE proteins

A

SNARE hypothesis

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22
Q

def: SNARE proteins found on vesicles

A

v-SNARE

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23
Q

def: SNARE proteins found on target membranes

A

t-SNARE

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24
Q

T or F: v- and t-SNAREs are not complementary molecules to each other

A

False, they are complementary molecules

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25
v- and t-SNARE __________ intertwine, pulling the membranes together
alpha helices
26
in vitro, the v-SNARE--t-SNARE interaction is strong enough to cause _______ ______, but in vivo, a rise in ____ _________ is thought initiate fusion
membrane fusion, Ca2+ concentration
27
T or F: After fusion, the v- and t-SNARE are still tightly associated, and are now in the same membrane
true
28
how do v- and t-SNAREs dissociate after membrane fusion has occurred?
- require NSF and SNAPs to pry apart the SNAREs, using energy from ATP hydrolysis
29
where do v-SNAREs go after the vesicle transport has occurred?
they are shuttled back to the previous compartment to repeat this process
30
what is the main difference between how COPI- coated vesicles are formed compared to COPII
they use different coat and adaptor proteins
31
def: aka a secretory pathway, vesicle contents are released to the exterior, vesicle membranes fuses with the plasma membrane
exocytosis
32
def: imports extracellular molecules by forming vesicles with the plasma membrane, in steady state with exocytosis
endocytosis
33
def: some vesicles move directly to the cell surface and immediately fuse with the plasma membrane, this process is unregulated and continuous and independent of external signals
constitutive secretion
34
what is an example of constitutive secretion?
mucus secretion by the intestinal lining
35
what does current evidence suggest about constitutive secretion?
that some tags may be required for it to occur
36
def: vesicles involved in this kind of exocytosis accumulate in the cell and only fuse with the plasma membrane in response to specific signals (like Ca2+)
regulated secretion
37
immature regulated secretory vesicles bud from the ____
TGN
38
def: the concentration of secretory proteins
condensation
39
where do mature secretory vesicles move to and remain there until receiving a signal?
move close to the site of secretion
40
what is membrane fusion triggered by
hormonal or chemical signals
41
def: when specific proteins need to be secreted from a limited region of the plasma membrane
polarized secretion
42
where is polarized secretion common?
in nerve cells and intestinal cells
43
how is polarized secretion regulated?
temporally
44
def: proteins in vesicles are released to the exterior of the cell as the vesicle fuses with the plasma membrane
exocytosis
45
proteins and lipids are added to the membrane via ________
exocytosis
46
def: essential nutrients are ingested by the cell as vesicles bud inwards off of the plasma membrane
endocytosis
47
proteins and lipids are removed from the membrane via ________
endocytosis
48
def: one of the primary ways that cells maintain membrane and fluid balance
bulk-phase endocytosis
49
does bulk phase endocytosis ingest or concentrate PARTICULAR molecules
no, non-specific
50
bulk phase endocytosis compensates for ________ ________ _____ by exocytosis and maintaining the surface to volume ratio
plasma membrane gain
51
def: process in which cells can selectively and efficiently acquire macromolecules
receptor-mediated endocytosis
52
as receptor-ligand complexes diffuse laterally they encounter specialized regions called ______ _____, sites for collection and internalization of these complexes
coated pits
53
T or F: receptors are sparse in coated pit regions
False, they are concentrated in coated pits at 10-20X their level in the plasma membrane
54
what does the accumulation of complexes in the coated pits trigger?
the accumulation of Clathrin-coat proteins on the cytosolic side of the membrane = inducing a curvature and invagination of the pit
55
each clathrin molecule consists of:
- 3 heavy chains - 2 light chains - joined at the centre to make a triskelion
56
T or F: COPII molecules extensively overlap, while Clathrin does not
False, Clathrin molecules extensively overlap, while COPII does not
57
def: promotes the assembly of clathrin cage and recruitment of membrane receptors to the buddying vesicle
AP2, adaptor protein 2
58
def: binding of this changes the conformation of AP2, making the cargo binding site accessible
Phosphoinositide
59
what is required as clathrin accumulates around the budding vesicle to constrict and close the vesicle?
dynamin
60
def: a cytosolic GTPase that constrict and separates the vesicle from the plasma membrane
dynamin
61
as GTP is hydrolyzed, the dynamin ring ________, separating the vesicle from the plasma membrane
tighten
62
def: ingestion of large (>500nm) macromolecules, cell parts, or whole organisms
phagocytosis
63
in humans, when is phagocytosis used
mostly just restricted to white blood cells
64
contact with the "target" triggers the onset of phagocytosis, as folds in the membrane, ________, surround the object forming an intracellular _______ ________
pseudopods, phagocytic vacuole
65
def: a hydrolytic enzyme, cleaves one molecule into two molecules, with an optima pH of ~5.0
acid hydrolase
66
what causes the lowered pH in lysosomes
V-Type ATPases in the membrane which pump in protons
67
def: the vesicle budding from the plasma membrane as a result of bulk-phase or receptor mediated endocytosis
endocytic vesicle
68
def: the primary sorting station in the endocytic pathway. endocytic vesicle fuse with the early endosome and material is either recycled back to the cell membrane or targeted for degradation
early endosome
69
def: an organelle containing the full compliment of acid hydrolyses, but who's lumen has not reached pH 4.0-5.0. This is the site of intraluminal vesicle formation
late endosome
70
def: an organelle that is digestively active. There are 2 routes for a late endosome to mature into a lysosome
lysosome
71
what are the 2 routes of a late endosome to mature into a lysosome
1. the ATPase pumps can lower the pH of the late endosome, which activates the enzymes, there by generating a new lysosome 2. the late endosome can fuse with an existing lysosome
72
def: mediate the uptake of material that will be used by the cell, receptor will deliver the bound material to the early endosome, releasing it because of the lower affinity at higher [H+], then return to the cell membrane
housekeeping receptors
73
def: bind extracellular messengers that change the activity of the cell, these receptors will be degraded, reducing the sensitivity of the cell to further simulation
signalling receptors
74
phagocytic vacuoles become _______ by fusion with endosomes
lysosomes
75
phagocytosis and receptor-mediated endocytosis involve the degradation of _______ _______ brought into the cell
external materials
76
where do vesicles formed by receptor-mediated endocytosis fuse?
with vesicles of the TGN containing acid hydrolase
77
def: when there is only indigestible material left in the lysosome, it is called this
residual body
78
def: the digestion of old organelles and cell structures
autophagy
79
def: formation of an autophagic vacuole when an organelle becomes wrapped in a double membrane derived from the ER
macrophagy
80
def: a much smaller vacuole is formed surrounded by a single membrane
microphagy

MBB 231 (19 decks)

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