Membrane Trafficking Flashcards
what is a way for our cells to communicate with the outside world or larger body than found in the cells
plasma membrane
what do vesicles contain
cargo
exocytic (secretory) pathway
default pathway which is from the ER, Golgi, vesicles and outside of the cell
endocytic pathway
bringing things into the cell
retrieval pathway
Kdel signal sequence comes into play when it accidentally sends a protein out that was supposed to stay in the ER
Where do vesicles start
ER
vesicles must be
selective and targeted
budding off of donor compartment traps them in the
target compartment
are there markers on vesicle surfaces that determine their final destinations
yes
what do we rely on to know where things go in the cell
phosphotidylinositol
PI is
phosphorylated at particular ring positions by kinases unique to each organelle
what binds to PIPS to target vesicles
coat proteins
clathrin transport mechanism
endocytic
COPI transport mechanism
retrograde or retrieval
COPII transport mechanism
anterograde or exocytic or secretory
where does clathrin orginate
plasma mebrane
where does COPI originate
golgi
where does COPII originate
endoplasmic reticulum
clathrin coats form
coated pits in cytosol
a triskelion is composed of
3 heavy and 3 light polypetide chains
do triskelions spontaneously assemble
yes in a symmetrical basket structure even without the membrane
clathrin coats rely on a series of
adaptor proteins and membrane-bending proteins
when clathrin is released from the membrane they are transported
naked
two functions of adaptins
- bind to clathrin coat to the membrane
- trap transmembrane proteins that capture soluble cargo molecules inside the vesicle
adaptins come in and facilitate recruitment of cargo receptors to…
recruit clathrin
adaptor proteins form an…
inner vesicle coat
the bud formation is what kind of dominated process
clathrin
do you need energy for the bud formation of clathrin
no it forms in absence of energy
the basket structure by triskelion forces the flexible membrane to buldge inward called
invaginaiton
what helps pinch off the vesicle after the budding process
dynamin
is dynamin an ATPase or GTPase
GTPase
what does dynamin do
hydrolyzes GTP rapidly and tightens itself around the tail to form vesicle
what kind of binding domain does dynamin have
PI(4,5)P2
dynamin wraps so tightly forcing the two inside leaflets of the vesicle membrane to
fuse
once dynamin does its job
we strip the coat
what recruits dynamin
PIPS
if there are no PIPS we loss
affinity for clathrin and dynamin
how do we strip the coat of clathrin
we have chaperone proteins that will act as ATPases
what chaperone protein strips the clathrin coat
HSP70
PIP phosphatases inside the vesicle which depletes PI(4,5)P2 from membrane weakening
the adaptor proteins
COPII requires what pathway
exocytic pathway
COPII vesicle assembly requires a
Sar1 Coat-recruitment GTPase
inactive Sar1-GDP is converted to what and by what
Sar1-GTP by Sar1-GEF
the inactivation of Sar1-GDP exposes an
amphiphilic helix which embeds Sar1 in the ER membrane
Sar1-GEF is only found in the
er membrane
how does Sar1 know to go to the er membrane
it is the only place where it gets turned on
when a vesicle needs to bud off the er the Sar1-GDP will come down and associate with
Sar-GEF
Sar-GEF kicks off GDP and allows
GTP to bind
Sar1-GTP changes the shape and tail which makes the tail
pop out and be exposed to the cytosolic side of the er membrane
Sar1-GTP recruits
adaptor proteins
Sar1-GTP binds to adaptor proteins which are
Sec 23 and Sec24
Sec24 binds to
cargo receptors
Sec23/24 start to
invaginate the membrane
Adaptor proteins in COPII recruit
outer coat proteins
what proteins in COPII form the outer coat and pinches off the vesicle?
Sec13/31
COPII uncoating we hydrolyze Sar-GTP to
Sar-GDP
once GTP in COPII is hydrolyzed the coat disassembles and Sar1-GDP returns to
its inactive, cytosolic form
are vesicles always round in COPII
no
what pathway does COPI require
retrieval pathway
COPI is the same as COPII but with different
GTPases and coat proteins
COPI vesicles require what GTPase
Arf1-GDP and Arf1-GTP
What GTPases are exposed on the surfaces of membranes
Rab Proteins
there are more than how many rab proteins
60
rab effectors act as …
tethers to catch the vesicle
can the rab split around the cytoplasm
yes
inactive rabs (rab-GDP) are found in the
cytosol
do Rab-GEFs activate rabs (to rab-GTP) on both vesicles and target membrane
yes
active rab-GTP binds to
membranes
effectors include
motor proteins and tethering proteins
motor proteins move
vesicles along cytoplasm
tethering proteins link
two membranes together
what do we kick off when rab proteins guide the vesicles
GDI
GDI is
GDP dissociation inhibtor
what mediates membrane fusion
snares
what do snares do
fuse the membranes together
snares exist in
complement
v-SNARE is on
the vesicle
t-SNARE is on
the target membrane
what side are snares on
cytosolic side
how do snares cause membrane fusion
the t-snare and v-snare wrap around so tightly causing fusion
SNAREs form 4-helix bundles that
exclude water
does the water layer between membranes prevent fusion
yes that is why we need snares
disassembly of snares require
energy
the helical bundles of snares are
energetically favorable
pulling snares apart require the action of
NSF
NSF is an
ATPase
COPII vesiciles exit the er on
smooth er
soluble proteins need an exit ticket to the er and must be
folded properly
as we send vesicles out you to the golgi you …
strip the coat off
everything that needs to be moved in a cell has to be moved along ? and transported through by
microtubules
motor proteins
ER vesicles come together to form larger
VTCs or vesicular tubular clusters
VTCs bud off on their own transport vesicles and return escaped proteins and proteins needed only for? and is called
budding
retrieval transport
ER proteins are retrieved in COPI vesicles via
KDEL signal sequences
KDEl receptors are sent back to ER in
COPI vesicles derived from VTC
KDEL is what type of terminal amino acid sequence
C-terminal
Where do KDEL receptors orginate
ER
what prevents KDEL receptors from binding in the wrong place?
pH
ER to golgi does what to pH
decreases it
what is the sorting center of the cell?
golgi
cis side is closest to the…
ER
trans cisterna is …
outside of the cell
true or false: there are a series of protein modification enzymes in each cisterna
true
traffic is what direction within the golgi?
one-way, though some vesicles are sent back to the ER
are things completely changed throughout the golgi process
yes
internal membrane proteins are highly glycosylated to protect them from
proteases
hydrolases work in a basic or acidic environment
acidic
the lysosome is a cellular stomach because it
routes things that are in vesicles to be degraded and destroyed or recycled
autophagy
cellular structures are no longer functional or needed
receptor-mediated endocytosis
endosomes from cell membrane containing molecules that must be processed. these can fuse with lysosomes
phagocytosis
large particles and microorganisms from the outside
pinocytosis
cellular drinking/ pulling in extracellular fluid
3 sources of digestive material can fuse with lysosomes
autophagy, endocytosis, phagocytosis
where does autophagy originate
cytoplasm of the cell
receptor-mediated endocytosis is what kind of mediated process
clathrin
receptors in endocytosis are embedded where
plasma membrane
receptors embedded in the plasma membrane bind to
extracellular cargo and bring it into the cell
receptors are recycled through
exocytosis back to PM
cargo is sent to the
golgi for sorting or lysosome for destruction
is cholesterol bad
no
HDL
high density lipoprotein
can cholesterol dissolve in blood
no its hydrophobic
how is cholesterol transported through the bloodstream
through carriers called lipoproteins
LDL
low density lipoprotein
Is HDL bad or good
good
is LDL bad or good
bad
most cholesterol hormones exist in what form
LDL form
hydrolytic enzymes in the lysosome convert the cholesterol esters to
free cholesterol
two examples that exhibit phagocytic cells
macrophages and neutrophils
exocytosis consists of 2 pathways
constitutive secretion (common)
regulated secretion
in constitutive secretion if the secretory vesicle is not tagged,…
it will leave the trans golgi and fuse with the cell membrane
in regulated secretion, the secretory vesicles store the molecule until
some signal stimulates their fusion with the cell membrane and release of contents
in regulated secretion the secretory vessels wait near the…
plasma membrane until signaled to release their contents
histamine secretion is in what cells
mast
what emplys an intricate system of targetted exocytosis and endocytosis to send/receive appropriate signals
neurons
