lec 14-15. vesicular trafficking Flashcards
orientation in biological membranes
- membranes stay the same
- lipids flip
SNAREs
provide specificity in vesicle targeting
ER translocation
moving proteins from cytosol into ER
RER vs SER
RER - has ribosomes which synthesize proteins
SER - makes lipids and trigylceries, stores Ca+
co-translational translocation
protein is being put into the ER while being translated
post-translational translocation
protein is made by ribosomes, folded by chaperones, then moved into an organelle
(sometimes ER, but more common mitochondria, peroxisomes, chloroplast)
signal hypothesis
ER translocated requires a signal, so if a protein has an amino acid sequence encoding a signal sequence, then it can be translated + cotranslated
how a protein is translocated
the signal sequence on the n-terminus anchors it into the membrane, while the rest of the protein goes into the lumen through the translocator (Sec61). Then signal sequence is cut off with signal peptidase and translocator shuts
how a membrane protein is translocated
they have an additional stop-transfer sequence in the middle (TMD) which tells the translocator to close
types of membrane protein
type 1 - N-terminus in lumen
type 2 - C-terminus in lumen
BIP
an ER chaperone that associates with new antibodies and makes sure they stay in lumen until correctly assembled
diseases associated with misfolded proteins
cystic fibrosis gauchers emphysema liver damage hypothroidism
essential components of COPII for vesicle formation
1) GTPase (Sar1)
2) adaptor proteins (sec23/24)
3) coat (13/31)
4) ATP and GTP
GTPases in vesicle formation
inactive GDP (Sar1-GDP) is converted into active GTP (Sar2-GTP) by GEF. The active GTP and interact with other proteins - it recruits adaptors and identifies the ER exit site
GTPase with the help of GAPs can then convert GTP back into GDP
adaptors
recognise and select cargo + link the transmembrane cargo to the outer coat.
they work by recognising the messages in cytoplasmic domains of membrane proteins
