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
Q

v- and t-SNARE __________ intertwine, pulling the membranes together

A

alpha helices

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26
Q

in vitro, the v-SNARE–t-SNARE interaction is strong enough to cause _______ ______, but in vivo, a rise in ____ _________ is thought initiate fusion

A

membrane fusion, Ca2+ concentration

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27
Q

T or F: After fusion, the v- and t-SNARE are still tightly associated, and are now in the same membrane

A

true

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28
Q

how do v- and t-SNAREs dissociate after membrane fusion has occurred?

A
  • require NSF and SNAPs to pry apart the SNAREs, using energy from ATP hydrolysis
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29
Q

where do v-SNAREs go after the vesicle transport has occurred?

A

they are shuttled back to the previous compartment to repeat this process

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30
Q

what is the main difference between how COPI- coated vesicles are formed compared to COPII

A

they use different coat and adaptor proteins

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31
Q

def: aka a secretory pathway, vesicle contents are released to the exterior, vesicle membranes fuses with the plasma membrane

A

exocytosis

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32
Q

def: imports extracellular molecules by forming vesicles with the plasma membrane, in steady state with exocytosis

A

endocytosis

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33
Q

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

A

constitutive secretion

34
Q

what is an example of constitutive secretion?

A

mucus secretion by the intestinal lining

35
Q

what does current evidence suggest about constitutive secretion?

A

that some tags may be required for it to occur

36
Q

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+)

A

regulated secretion

37
Q

immature regulated secretory vesicles bud from the ____

A

TGN

38
Q

def: the concentration of secretory proteins

A

condensation

39
Q

where do mature secretory vesicles move to and remain there until receiving a signal?

A

move close to the site of secretion

40
Q

what is membrane fusion triggered by

A

hormonal or chemical signals

41
Q

def: when specific proteins need to be secreted from a limited region of the plasma membrane

A

polarized secretion

42
Q

where is polarized secretion common?

A

in nerve cells and intestinal cells

43
Q

how is polarized secretion regulated?

A

temporally

44
Q

def: proteins in vesicles are released to the exterior of the cell as the vesicle fuses with the plasma membrane

A

exocytosis

45
Q

proteins and lipids are added to the membrane via ________

A

exocytosis

46
Q

def: essential nutrients are ingested by the cell as vesicles bud inwards off of the plasma membrane

A

endocytosis

47
Q

proteins and lipids are removed from the membrane via ________

A

endocytosis

48
Q

def: one of the primary ways that cells maintain membrane and fluid balance

A

bulk-phase endocytosis

49
Q

does bulk phase endocytosis ingest or concentrate PARTICULAR molecules

A

no, non-specific

50
Q

bulk phase endocytosis compensates for ________ ________ _____ by exocytosis and maintaining the surface to volume ratio

A

plasma membrane gain

51
Q

def: process in which cells can selectively and efficiently acquire macromolecules

A

receptor-mediated endocytosis

52
Q

as receptor-ligand complexes diffuse laterally they encounter specialized regions called ______ _____, sites for collection and internalization of these complexes

A

coated pits

53
Q

T or F: receptors are sparse in coated pit regions

A

False, they are concentrated in coated pits at 10-20X their level in the plasma membrane

54
Q

what does the accumulation of complexes in the coated pits trigger?

A

the accumulation of Clathrin-coat proteins on the cytosolic side of the membrane = inducing a curvature and invagination of the pit

55
Q

each clathrin molecule consists of:

A
  • 3 heavy chains
  • 2 light chains
  • joined at the centre to make a triskelion
56
Q

T or F: COPII molecules extensively overlap, while Clathrin does not

A

False, Clathrin molecules extensively overlap, while COPII does not

57
Q

def: promotes the assembly of clathrin cage and recruitment of membrane receptors to the buddying vesicle

A

AP2, adaptor protein 2

58
Q

def: binding of this changes the conformation of AP2, making the cargo binding site accessible

A

Phosphoinositide

59
Q

what is required as clathrin accumulates around the budding vesicle to constrict and close the vesicle?

A

dynamin

60
Q

def: a cytosolic GTPase that constrict and separates the vesicle from the plasma membrane

A

dynamin

61
Q

as GTP is hydrolyzed, the dynamin ring ________, separating the vesicle from the plasma membrane

A

tighten

62
Q

def: ingestion of large (>500nm) macromolecules, cell parts, or whole organisms

A

phagocytosis

63
Q

in humans, when is phagocytosis used

A

mostly just restricted to white blood cells

64
Q

contact with the “target” triggers the onset of phagocytosis, as folds in the membrane, ________, surround the object forming an intracellular _______ ________

A

pseudopods, phagocytic vacuole

65
Q

def: a hydrolytic enzyme, cleaves one molecule into two molecules, with an optima pH of ~5.0

A

acid hydrolase

66
Q

what causes the lowered pH in lysosomes

A

V-Type ATPases in the membrane which pump in protons

67
Q

def: the vesicle budding from the plasma membrane as a result of bulk-phase or receptor mediated endocytosis

A

endocytic vesicle

68
Q

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

A

early endosome

69
Q

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

A

late endosome

70
Q

def: an organelle that is digestively active. There are 2 routes for a late endosome to mature into a lysosome

A

lysosome

71
Q

what are the 2 routes of a late endosome to mature into a lysosome

A
  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
Q

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

A

housekeeping receptors

73
Q

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

A

signalling receptors

74
Q

phagocytic vacuoles become _______ by fusion with endosomes

A

lysosomes

75
Q

phagocytosis and receptor-mediated endocytosis involve the degradation of _______ _______ brought into the cell

A

external materials

76
Q

where do vesicles formed by receptor-mediated endocytosis fuse?

A

with vesicles of the TGN containing acid hydrolase

77
Q

def: when there is only indigestible material left in the lysosome, it is called this

A

residual body

78
Q

def: the digestion of old organelles and cell structures

A

autophagy

79
Q

def: formation of an autophagic vacuole when an organelle becomes wrapped in a double membrane derived from the ER

A

macrophagy

80
Q

def: a much smaller vacuole is formed surrounded by a single membrane

A

microphagy