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Biology Exam 2 > Vesicular Transport > Flashcards

Vesicular Transport Flashcards

1
Q

transportation of proteins and other biomolecules

A

vesicular transport

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2
Q

cargo

A

the contents of vesicles

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3
Q

vesicular transport is _____ .

A

directional

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4
Q

vesicular transport

A

a continuous exchange of components between various membrane bound compartments

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5
Q

cues for incoming traffic

A
  1. composition of memb.

2. molecular markers on memb. surface

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6
Q

molecular address

A

combination of molecular markers

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7
Q

return of molecules to the source

A

retrieval pathway

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8
Q

how does a cell segregate proteins

A

cells segregate proteins into membrane domains by assembling a cytosolic coat

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9
Q

2 major functions of vesicle coats

A
  1. pulls specific proteins into a specialized patch

2. molds the vesicle into a basket like structure

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10
Q

loss of coat

A

coat is discarded after the vesicle has budded off and before it fuses with target

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11
Q

list the types of coats

A
  1. clathrin
  2. COPI
  3. COPII
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12
Q

clathrin direction

A

mediate transport from golgi and from plasma membrane

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13
Q

major protein in clathrin coated vesicles

A

clathrin

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14
Q

clathrin structure

A
  • each subunit has 3 small and 3 large polypeptide chains

- which for a 3 - legged structure

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15
Q

what is the structure of clathrin called?

A

triskelion

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16
Q

overall clathrin structure

A

assembled into basket shapes

  • hexagon/pentagon forming the basket
  • form coated pits on cytosolic side
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17
Q

second layer between cage and membrane

A

cage = coat

adaptor proteins

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18
Q

role of transmembrane proteins in clathrin coated vesicles

A
  1. receptors that bind to cargo inside
  2. allows cargo to be trapped within vesicle
  3. adaptor proteins bind on outside
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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
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20
Q

assembly of clathrin vesicles: adaptor proteins

A
  1. bind to transmembrane proteins that are bound to cargo interiorly
  2. bind to clathrin proteins
  3. allow for selective recruitment of cargo and coating molecules
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21
Q

dynamin is involved in _____ of clathrin coats.

A

budding off —- which ultimately causes the clathrin coat to disassemble

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22
Q

pinching

A

bringing of 2 cytosolic sides together to allow fusion and release of bud as a vesicle

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23
Q

function of dynamin

A
  1. assembles ring around neck of a budding off vesicle

2. squeezes and cuts the bud off

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24
Q

dynamin domains

A
  1. PIP2 binding domain – tethers protein to membrane

2. GTPase domain – regulates rate of pinch off

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25
Q

dynamin also recruits other ….. ?

A

other proteins to distort the lipid bilayer via lipid modifying enzymes that change the lipid composition

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26
Q

vesicle loses coat

A

PIP2 is degraded after budding off

- results in weakening of binding of coat to adapter proteins

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27
Q

role of HSP70 in clathrin coats

A

uses ATP to peel off the clathrin coat after PIP2 has become degraded (which occurs after budding)

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28
Q

COPI

A
  • mediates transport from golgi cisternae

- important in retrieval pathway

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29
Q

COPII

A
  • mediates transport from ER
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30
Q

plays a major role in coat assembly, vesicle formation and protein trafficking

A

phosphoinositide

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31
Q

functions of phosphoinositide

A
  1. mark organelles/membrane domains for target
  2. control recruitment/binding of specific proteins per specific destination
  3. regulate vesicle trafficking
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32
Q

de-phos/phosphorylation of phosphoinositide

A
  • occurs at 3,4,5’ positions
  • form various derivatives
  • each has their own unique actions
  • can interconvert between derivates
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33
Q

interconversions between phosphoinositides

A
  • highly compartmentalized
  • specific to organelle or domain
  • facilitated by PI kinases and phosphates —- different organelles have unique sets of these
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34
Q

____ binds with high _____ to the ____ groups of phosphoinositides.

A

protein
specificity
head groups

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35
Q

membrane bending proteins

A

BAR domains

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36
Q

BAR domain structure

A
  • coiled coils

- + charge towards inner surface which is in contact with the (-) charged membrane

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37
Q

BAR domain function

A
  • their + charge interacts with (-) memb.

- causes memb. to bend/bow outward

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38
Q

Rab and SNAREs are involved in ______ .

A

vesicle targeting

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39
Q

list the 2 important factors involved in vesicle targeting

A
  1. Rab

2. SNAREs

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40
Q

role of rab

A

direct vesicles to specific domains on target membrane
~60 types
monomeric GTPase

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41
Q

forms of rab

A
  1. inactive-cytosolic-GDP

2. active-membrane bound-GTP

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42
Q

inactive rab

A
  1. GDP form
  2. kept inactive by the binding of GDI
  3. this form is soluble
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43
Q

GDI

A

GDP dissociation inhibitor

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44
Q

active rab

A
  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.
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45
Q

rab effectors

A
  • present on target memb.
  • motor/tethering proteins
  • facilitate memb. tethering and fusion of vesicle
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46
Q

list the types of Rabs for exam

A
  1. Rab1
  2. Rab3A
  3. Rab5
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47
Q

rab1

A

ER and golgi complex

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48
Q

rab3a

A

synaptic vesicles

secretory vesicles

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49
Q

rab5

A

early endosomes
plasma memb.
clathrin-coated vesicles

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50
Q

role of SNARE proteins

A
  • mediate fusion of vesicle with memb.
  • 35 different types
  • exist as complimentary pairs
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51
Q

forms of SNARE

A
  1. v-snare

2. t-snare

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52
Q

v-snare

A

vesicular snare

  • single polypeptide
  • found on vesicle memb.
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53
Q

t-snare

A

target snare

  • 2-3 proteins
  • found on target membrane location
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54
Q

snare mechanism

A
  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
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55
Q

triggering of fusion

A

may be triggered by extracellular signals which remove inhibitory proteins which were preventing fusion

56
Q

dissociated of snare pairs

A

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
Q

protein options w/in ER

A
  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
Q

newly ER synthesized proteins are packaged into ____ coated vesicles and then ?

A

COPII

-bud off from ER exit sites

59
Q

exit signals

A
  • displayed by proteins on cytosolic surface

- recognized by receptors present on COPII coat

60
Q

fate of damaged/misfolded proteins in ER lumen

A

chaperones bind to them and degrade them for recycling

61
Q

ER lumen chaperones

A

BiP and calnexin

for damaged proteins

62
Q

vesicular tubular _____ .

A

clusters

-vesicles can fuse together after shedding their coat to form larger structures

63
Q

fusion of several vesicles requires ____ .

A

snares

both v and t types

64
Q

types of vesicle clusters

A
  1. homotypic - same cargo/same origin

2. heterotypic - dif. cargo/dif. origin

65
Q

properties of vesicular tubular clusters

A
  • short lived
  • move along microtubules to golgi via motor proteins
  • fuse w/ golgi to deliver contents
66
Q

vesicles budding off golgi to get to ER are coated with ____ ?

A

COPI

67
Q

ER retrieval signals

A
  1. kkxx

2. kdel

68
Q

ER retrieval signal present in ER membrane proteins

A
  • 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
Q

ER retrieval signal present in _____ proteins at the ___ terminus .

A
  • 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
Q

cisternae

A

golgi is a collection of flattened membrane enclosed compartments called cisternae

71
Q

faces of the golgi complex

A
  1. cis or entry — faces ER

2. trans or exit — faces plasma memb.

72
Q

CGN

A
  • cis golgi network
  • network of fused vesicular tubular cluster from ER
  • proteins/lipids enter golgi from CGN
73
Q

TGN

A
  • trans golgi network
  • regions that allow exit of proteins/lipids
  • next step of secretory pathway
74
Q

golgi also plays an important role in _____ .

A

protein glycosylation

75
Q

golgi hypotheses

A
  1. cisternal maturation model
  2. vesicle transport model

research supports both models — describe how the golgi maintains it’s dynamic shape

76
Q

lysosomes

A

membrane enclosed compartments filled with 40 types of enzymes important for intracellular digestion

derived from late endosomes

77
Q

what are the lysosome enzymes collectively referred to as?

A

hydrolases

78
Q

2 things lysosomes require

A
  1. acidic internal environment

2. proteolytic cleavage for activation

79
Q

vacuolar ATPase

A
  • on lysosomal membrane

- pumps H+ inside to maintain low pH and to drive transport of small metabolites

80
Q

what happens post digestion?

A

-lysosome pumps end products out into cytosol for recycling

81
Q

list steps of lysosome maturation

A
  1. early endosome
  2. late endosome
  3. endolysosome
  4. lysosome
82
Q

autophagy

A
  • -when an organelle is damaged or old and needs to be rid off
  • -cell delivers to lysosome for breakdown
83
Q

model of autophagy

A
  1. induction
  2. closure-autophagosome
  3. fusion - w/ lysosome
  4. digestion
  5. return to normal lysosome state
84
Q

describe induction phase of autophagy

A

cell forms a bunch of little vesicles containing engulfed cytosol
join together to form a large compartment

85
Q

describe closure phase of autophagy

A

the large form of joined compartments circle completely around the damaged material

  • now termed autophagosome
  • has double membrane
86
Q

transport from TGN to ….

A

pathway that delivers membrane proteins and hydrolases to lysosomes

  • -buds off TGN = endosomes
  • -can develop into lysosomes
87
Q

sorting signal for lysosomal proteins

A

mannose-6-phosphate (sugar signal)
M6P
is attached to proteins in the CGN

88
Q

proteins after budding off from TGN

A
  • -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
Q

protein-M6P budding off from TGN

A

M6P signal binds to specific receptors, clathrin coat forms and vesicle buds off, loses coat
now an endosome

90
Q

addition of signal to lysosomal hydrolase

A
  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
Q

what results if defects exist in lysosomal hydrolases?

A

accumulation of undigested material in the lysosome

92
Q

hurler’s disease

A

mutation in the enzyme required to break down GAGs

93
Q

inclusion cell disease

A
  1. all lysosomal hydrolases are missing

2. undigested material accumulates = inclusions

94
Q

enzyme that adds M6P

A

GIcNAc–phosphotransferase

95
Q

what happens if there is a defect in the enzyme responsible for adding M6P?

A

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
Q

uptake of macromolecules from exterior

A

endocytosis

97
Q

in endocytosis, material is progressively enclosed by a portion of the _____ .

A

plasma membrane

98
Q

describe general endocytosis mechanism

A
  1. PM invaginates
  2. pinches off
  3. which forms endocytic vesicles or endosome
99
Q

large particles ingested by vesicles called ______

A

phagocytosis
phagosomes

a specialized form of endocytosis, only done by WBCs

100
Q

small particles ingested by vesicles

A

pinocytosis

or cell drinking

101
Q

used to import select macromolecules from outside cell

A

receptor-mediated endocytosis
provides selective concentration
ex = cholesterol intake

102
Q

describe receptor-mediated endocytosis

A
  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
Q

blockage of cholesterol intake pathway

A

atherosclerosis

104
Q

fate of endocytosed receptor proteins

A

enveloped in transport vesicle = transcytosis

reinserted in PM to be used again

105
Q

insulin binds to an insulin receptor, causing ….?

A

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
Q

phagocytosis is carried out by?

A

phagocytes, WBCs such as macrophages and neutrophils

107
Q

phagocytes are capable of ingesting

A

microorganisms
senescent cells
apoptotic cells

108
Q

in order for phagocytes to digest their material ….

A

phagosomes fuse w/ lysosomes to degrade ingested material

109
Q

undigested material can be secreted out via

A

exocytosis

110
Q

phagocytosis is triggered by

A

binding of particles to receptors on phagocyte surface

antibodies bind to the microbe
Fc chain recognized by Fc receptor on phagocyte surface

111
Q

binding of phagocytes to material triggers

A

formation of pseudopod

which engulfs the particle to form a phagosome

112
Q

pseudopod formation is driven by ?

A

local actin polymerization and reorganization to surround the material and engulf it

113
Q

control of pseudopod formation

A

by Rho GTPases and phosphoinositide signaling

114
Q

pinocytosis occurs _____ in all eukaryotic cells

A

continuously

115
Q

pinocytosis process begins at _____

A

clathrin coated pits
PM invagination
pinch off
clathrin coated vesicle

116
Q

what is trapped within vesicles via pinocytosis

A

extracellular fluid w/ various solutes trapped in pits

117
Q

flask shaped invaginations in PM

A

caveolae

rich w/ cholesterol and glycosphingolipids and GPI anchoring proteins

118
Q

major structural protein of caveolae

A

caveolin

119
Q

caveola invaginate into membrane by their unique _____ and not the _____.

A

lipid composition not the protein coat

120
Q

______ pinches off caveolae from PM

A

dynamin

121
Q

endosome-like compartment from caveolae

A

caveosome

which do not connect with lysosomes

122
Q

transport vesicles move from TGN to PM

A

exocytosis

123
Q

in exocytosis, ______ and _____ in vesicles are destined for the _____

A

membrane proteins
lipids
PM

124
Q

______ secretory pathway operates continuously : exocytosis

A

constitutive

125
Q

_______ secretory pathway operates only when triggered by signals: exocytosis

A

regulated

126
Q

examples of signals for exocytosis

A

hormones

neurotransmitters

127
Q

3 paths for protein sorting in TGN

A
  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
Q

steps of forming a secretory vesicle

A
  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
Q

what happens to mature secretory vesicles before regulated exocytosis occurs

A
  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
Q

exocytosis SNAREs

A
  1. v-SNARE = synaptobrevin
  2. t-SNARE = syntaxin
  3. t-SNARE = SNAP25
  4. synaptotagmin
131
Q

list the phases of synaptic vesicle exocytosis

A
  1. docking
  2. priming I
  3. priming II
  4. fusion fore opening
  5. fusion complete
132
Q

synaptobrevin

A

v-SNARE of exocytosis synaptic vesicles

133
Q

syntaxin

A

t-SNARE of exocytosis synaptic vesicles

134
Q

SNAP25

A

second t-SNARE of exocytosis synaptic vesicles

helps syntaxin bring the vesicle into contact w/ PM by coiling w/ synaptobrevin

135
Q

synaptotagmin

A

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
Q

complexin

A

responsible for blocking synaptic vesicle fusion w/ presynaptic membrane until an action potential occurs

synaptotagmin stops complexin to allow fusion

Biology Exam 2 (9 decks)

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