2.1: Membrane Trafficking Flashcards
how do changes in gene expression lead to development
cell types, tissues, organs, organisms
how do cells change during development
numbers, shapes, functions, interactions
what are the 3 components of how are cells and tissues organized spatially
membrane trafficking, cytoskeletal networks, cell adhesion
cell _________ is essential for multicellular organisms
polarization
polarized cells can (3 points)
- have different functions at different cell regions
- define inside vs outside
- transmit signals from one end to the other
membrane trafficking can send proteins to different _________, determines where the proteins____ _____
domains, end up
there are two methods of membrane trafficking, exocytosis and exocytosis->endocytosis, how do they differ in destination specificity
- exocytosis: directly to the target domain after sorting in the tgn
- exocytosis to any domain then endocytosis followed by recycling to the target domain
how do vesicles ensure they are going to the right location
rabs w/ tethering proteins
what are sorting stations used for (+ give examples)
where proteins are organized, example is tgn and endosomes
- are trafficking routes polarized? (give examples)
- different routes are balanced by what? (give examples)
- yes they are polarized (bc diff beginning and ends: eg er -> golgi -> pm and pm->early endosome->lysosome)
- different routes are balanced by retrieval pathways (eg er retrieval from golgi and resecretion to pm)
what is the default pathway in membrane trafficking and describe it
constitutive secretion is default: most cargo moves like this, specific signals do not seem to be required for constitutive secretion
do all eukaryotic or prokaryotic cells have constitutive secretion
eukaryotic, think abt it, do prokaryotic cells have golgi or smth
clathrin coated vesicles can return membrane back to the golgi, what does this do to the vesicle and cargo
secretion can release concentrated cargo. this isn’t just for the constitutive pathway.
this shrinks the vesicle and makes the cargo more concentrated = mature secretory vesicle
describe regulated secretion
regulated secretion can release materials in response to a signal.
regulated secretion vesicles are fully formed but do not fuse with the pm until a signal is received. the vesicles still can come from the tgn.
eg mast cell releasing stored histamine
in which 3 situations will regulated secretion deliver extra membrane material
a) cytokinesis: the 2 cells need extra cell membranes to bud
b) phagocytosis: it forms the vesicle (a membrane bound container) to take in substance
c) plasma membrane repair: eg wound repair
endocytosed proteins have 3 options, what are they
- recycling to the same domain of the pm eg if it took something in, gets sorted in the endosome, the vesicle can go back to the same pm
- transcytosis to the other domain of the pm
- degradation in the lysosome
describe cholesterol uptake as an example of exocytosis
- ldl (low density lipoprotein) gets enveloped in clathrin coated vesicles, clathrin gets uncoated after, and the vesicle fuses to early endosome
- the ldl receptor that initially took it in, returns to pm through recycling after early endosome
- ldl in early can go to late endosome
- later, in the endolysosome there are hydrolytic enzymes which result in the degradation of ldl and it leads to free cholesterol which can go through transcytosis to wherever it is needed
- hydrolytic enzymes stay in lysosomes
broadly describe the 3 types of membrane changes during vesicle trafficking
- forming: vesicle forms from the donor membrane into the cytoplasm – contents could be from outside cell or the cell lumen
- fusion: vesicle merges with a target membrane (could be expelling contents into outside cell or lumen are merging)
- changes: vesicle forms from a donor membrane away from the cytoplasm (from cytosol to outside cell)
________ can mediate vesicle formation into the cytoplasm
clathrin
explain how clathrin can mediate vesicle formation into the cytoplasm
- cargo receptors on the donor membrane select for the cargo
- an adaptor protein from the inside of cell (ie cytosol) help clathrin coat
- budding begins
- vesicle forms w the help of membrane bending and fission proteins into coated coated vesicle
- vesicle gets uncoated = naked transport vesicle
- recall that vesicle coats are selective of cargo and specifically targeted (copII goes from er to golgi, copI is around golgi and back to er, clathrin can go from golgi to endosomes and ecm to endosomes etc)
t-snares and v-snares must be on same or opposite membranes to help mediate vesicle fusion
opposite membranes
which type of membrane changes are ESCRT proteins related to
vesicle changes: vesicle forms from a donor membrane away from the cytoplasm
explain how escrt proteins can form vesicles away from the cytoplasm
- vesicles can form away from the cytoplasm into ec space
- vesicle formation machinery is in the cytoplasm
- often used for cytokinesis but gets hijacked by viruses so the virus particle from the cytosol leaves into ec space using this sort of transport
- escrt-0 is on PI(3)P and a signaling receptor w ligand attached which has a monoubiquitin
- escrt-0 passed it to 1 then 2 then at 3 it promotes budding and escorts the virus leaving the cell
- the endosome membrane forms the intralumenal vesicle
How many of the following are examples of vesicle formation into the
cytoplasm?
* COPII-mediated secretory vesicle formation at the ER
* ESCRT-mediated vesicle formation
* clathrin-mediated endocytic vesicle formation
* any process mediated by SNARE proteins
a) 0
b) 1
c) 2
d) 3
c) 2
statement 1 and 3 are correct. 2 is wrong bc it leaves the cell, not into the cytoplasm. 4 is wrong bc its SNARE relates to fusion, not formation.
