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Biomed 2 > Cell Bio - Vesicle transport > Flashcards

Cell Bio - Vesicle transport Flashcards

1
Q

what is the secretory pathway

A

flow of membrane bound and soluble proteins destined for certain organelles or extracellular space

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2
Q

what is the endocytic pathway

A

plasma membrane capture of extracellular components and internalisation of membrane proteins into vesicles for recycling or degradation

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3
Q

purpose of coat proteins

A

Provides shape to membranes to “curve” and bud
Determine the size and shape of the vesicle
Concentrate the protein in the vesicle
Provide selectivity for the “cargo”
Determine the vesicle’s destination

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4
Q

where do clathrin coated vesicles go from and to

A

trans-Golgi network (TGN) to endosome and plasma membrane (via endocytosis)

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5
Q

where do COPI and COPII coated vesicles go from and to

A

COPI - Golgi complex to the ER (retrieval)
COPII - ER to Golgi

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6
Q

how does a protein associate with the plasma membrane via a helix

A

protein forms an amphipathic α-helix within the cytosolic face that anchors it

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7
Q

how does a protein covalently and and non-covalently associate with the plasma membrane

A

covalent - Covalent attachment of lipid group – fatty acid or prenyl group
non-covalent - Non-covalent interactions with other membrane bound proteins

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8
Q

what forms non-covalent bonds with proteins in the plasma membrane

A

peripheral proteins

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9
Q

structure of clathrin and where is it formed

A

subunits made of 3 heavy and 3 light chains - assemble to form triskelions
formed at the trans-Golgi network/plasma membrane
clathrin forms an outer protein lattice

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10
Q

what are the various types of endocytosis

A

receptor-mediated endocytosis
phagocytosis
pinocytosis

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11
Q

during endocytosis what is required for clathrin recruitment and coat formation

A

recruitment of AP2 adaptor protein

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12
Q

what is the purpose of AP2 adapter protein

A

binds to specific phospholipids results in conformational change that allows binding to cargo receptors on cell surface, triggers membrane curvature

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13
Q

structure of AP2 adapter protein

A

heterotetrameric, multi sub-unit:
α-adaptin
β2-adaptin
σ2-chain
µ2-chain

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14
Q

what is required for AP2 adaptor protein to enter its open conformation and exposes the clathrin binding site

A

clathrin binding site is buried in AP2 in locked, soluble state
binding to PIP2 on membrane exposes the clathrin binding motif in β2-adaptin
leads to AP2 open conformation

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15
Q

how does μ2-adaptin facilitate clathrin coat assembly

A

μ2-adaptin interacts with cargo which stabilises AP2 complex open conformation
thus aids in cathrin binding

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16
Q

what is the function of dynamin and what does it require

A

assists in vesicle and budding formation
requires GTP

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17
Q

what happens to the clathrin coated vesicle once it separates from the membrane

A

the clathrin coat dissociates immediately and the components are recycled
leaves behind a naked vesicle that is transported to its destination

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18
Q

structure of dynamin and what does it do in the presence of GTP

A

dynamin oligomerises to form a helical ring around the neck of the bud, recruits other proteins, and tethers itself to the membrane through lipid binding domains
dynamin constricts in the presence of GTP

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19
Q

what does GTP hydrolysis of dynamin result in

A

GTP hydrolysis of dynamin results in the lengthwise extension of helix, and fission of membrane

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20
Q

how are acid hydrolase enzymes modified to bind to what

A

N-glycosylated and phosphorylated by mannose-6 in Golgi
allows binding to M6P-receptor and trafficking to lysosome

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21
Q

structure of COPII protein

A

has 5 subunits
associated GTPase (SAR 1)

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22
Q

location and function of Sar-1 GEF

A

embedded in the donor membrane
recruits and activates Sar1 - loading with GTP

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23
Q

function of Sar1-GTPand what does it lead to

A

recruits Sec23/24 which interacts with cargo forming an inner coat

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24
Q

function of Sec13/31

A

forms the outer coat

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25
Q

what do ER proteins have at their C-terminus and what is it recognised by

A

KDEL
recognised by KDEL receptors in cis-golgi

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26
Q

what is required for coatemer recruitment and what activates it

A

ARF1 GTPase is required for coatomer recruitment,
activated by Golgi-localised GEF proteins

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27
Q

what do vesicles originating from plasma membrane require

A

Rab5

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28
Q

what is acquired from vesicle transport and maturation

A

Rab7

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29
Q

function of GDI

A

keeps Rab inactive in cytosol

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30
Q

outline Rab-GTPase activation

A

GDF – GDI displacement factor → displaces GDI from GDP bound form of Rab, thus allowing membrane anchor with its hydrophobic prenyl group

GEF mediated GDP to GTP exchange triggers a conformational change in the Switch 1 and 2 regions of Rab allowing interactions with effector proteins

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31
Q

what does activation of RabA-GEF to membrane lead to

A

locally activates RabA

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32
Q

function of RabA

A

activates effector proteins
RabB-GEF

33
Q

what does activation of RabB by RabB-GEF lead to

A

activation of RabB effector proteins
RabA-GAP

34
Q

function of RabA-GAP

A

inactivates RabA

35
Q

each V-SNARE protein on the surface of the vesicle has a corresponding what

A

corresponding T-SNARE protein on the surface of target membrane

36
Q

what is v/t-SNARE protein docking initiated by

A

Rab-GTPase

37
Q

what is step 1 of vesicle docking

A

Rab-GTP protein on vesicle surface binds to specific Rab-effector in target membrane

This brings v-SNAREs and t-SNAREs into close proximity -allowing docking

38
Q

what is step 2 of vesicle docking

A

a-helices of v-SNARE and t- SNARE form coiled-coils (trans-SNARE complex)

exerts inward force that brings the two membranes close together

39
Q

step 1 of membrane fusion

A

Lipid bilayers fuse by flowing into each other after being forced into close proximity

40
Q

step 2 of membrane fusion

A

A complex of two proteins (NSF and a-SNAP) binds to the “empty” SNARE complexes (cis-SNARE complex)

41
Q

step 3 of membrane fusion

A

ATP hydrolysis (catalysed by NSF) causes disassembly of the SNARE complexes and recycling

42
Q

outline the mechanism of coordinated synaptic membrane fusion and neurotransmitter release

A

Synaptic vesicles dock at presynaptic plasma membrane, with complexin keeping the trans-SNARE complex in a primed position

Calcium induces a conformational change in the complex allowing coordinated vesicle fusion with plasma membrane leading to neurotransmitter release

43
Q

what do multivesicular body’s (MVB’s) contain

A

intraluminal vesicles
lower pH

44
Q

what is the purpose of multivesicular body’s (MVB’s)

A

shield receptors from the cytosol - turns off potential transduction signals
is a method of control of signals via internalisation

45
Q

what happens as a consequence of ligand-receptor internalisation

A

results in the degradation of the receptor
inactivation of signalling cascade

46
Q

what is required for intraluminal vesicle formation

A

ESCRT (endosomal sorting complexes required for transport)

47
Q

what does ECRT-0 contain

A

ESCRT-0 contains ubiquitin binding domain which interacts with ubiquitylated receptor cargo
ESCRT-0 also contains binding domain for interaction with PI3P rich phospholipid on endosomal membrane

48
Q

what does the IP3 in early endosome act as

A

acts as a binding site for effector proteins

49
Q

what do ESCRT-0/I/II bind to

A

complexes bind to ubiquitylated cargo and the membrane phospholipid PI3P

50
Q

what is necessary for budding and scission

A

ESCRT’s-III and Vps4’s

51
Q

what is Hrs

A

Hrs is an ESCRT-0 protein that interacts with ubiquitin on cargo

52
Q

what is VPS4 (vacuolar protein sorting-associated protein 4)

A

is an ATPase that hydrolyses ATP to disassemble ESCRT complex allowing intraluminal vesicle to form

53
Q

what is the machinery required that can select cargo to be captured by autophagy and non-selective capture of cytosol during starvation

A

Atg8
Atg5-Atg12-Atg16 complex

54
Q

what is Atg8

A

Atg8 (also known as LC3) is a membrane protein that decorates inner and outer leaflets of autophagosome

55
Q

how is an amphisome formed

A

Following closure of the autophagosome, there are fusion events with endosomes and MVBs to form an amphisome

56
Q

what does formation of an amphisome lead to

A

results in a gradual reduction in internal pH and acquisition of machinery to facilitate fusion with the lysosome (e.g. SNARE components)

to form an autolysosome, resulting in proteolytic degradation of components

57
Q

what is non-selective autophagy used for

A

During nutrient starvation leading to low ATP levels or low amino acids, autophagy is activated resulting in the removal of bulk cytosol for harvesting of amino acids required for protein synthesis and energy production

58
Q

how are damaged cargo recognised by autpphagy receptors

A

they are decorated with polyubiquitin

59
Q

what do endocytic vesicles and clathrin coats also recruit

A

actin-nucleation promoting factor

60
Q

what is WASP

A

nucleation promoting factor that activated Arp2/3 complexes

61
Q

in terms of actin what does Arp2/3 promote and what does this lead to

A

Arp2/3 promotes actin polymerisation which drives internalised vesicles away from the plasma membrane

62
Q

how is WASP stored

A

WASP is held inactive in cytosol through intramolecular interaction that masks WCA domain

63
Q

how is WASP activated

A

interaction via GTPase through RBD

64
Q

what happens when WASP is activated

A

intramolecular interaction is relieved and W domain is exposed to bind actin and the A domain activates Arp2/3

65
Q

what is the angle between new and old fialment

A

70 degrees

66
Q

what does listeria possess instead of WASP

A

ActA

67
Q

what is required for a cell to migrate in the forward direction

A

Arp 2/3 activation and formation of branched actin at leading edge promotes membrane protrusion

68
Q

how much does the myosin head swing when moving an actin filament

A

30-40nm

69
Q

structure of golgins

A

Golgins are large proteins (over 30 genes), with coiled-coil domains adopting a rod-like shape

70
Q

features of golgins

A

Golgins involved in transport and vesicle tethering around regions of the Golgi
Act as Rab effector proteins
Golgins interact directly with microtubules, with microtubule associated proteins or microtubule motors, such as dynein
Contribute to Golgi positioning and morphology

71
Q

what does a loss of dynein lead to in terms of lysosomes

A

Lysosomes are positioned in perinuclear regions - loss of dynein leads to a dispersal of lysosomes throughout the cytoplasm

72
Q

structure of dynein

A

Cytoplasmic dynein complex contains a pair of identical heavy chains (homodimer)
Dynein heavy chain has an ATP-dependent motor (head), Microtubule binding stalk region, and N-terminal stem that binds cargo or adaptors
N-terminal stem interacts with intermediate and light chain proteins

73
Q

what does each dynein motor head contain

A

Each motor head domain contains a hexameric AAA ring – that has stalk, buttress, and linker regions protruding from AAA ring

74
Q

what is the size of each dynein step

A

8nm

75
Q

function of dynactin

A

a large complex linking dynein to cargo and regulating dynein activity
This complex can interact with a range of adaptor proteins, thus providing specificity for different cargo

76
Q

what are melanophores

A

cells in the skin that contain melanin-filled pigment granules called melanosomes

77
Q

what are melanosomes transported by

A

transported by kinesin-2 during dispersal, also tethered in the periphery by myosin actin motors (myosin V)

78
Q

what is responsible for melanosome aggregation

A

dynein-dynactin motors

79
Q

what regulates dispersion and aggregation of melanosomes

A

intracellular cAMP levels

Biomed 2 (18 decks)

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