*Path of transmembrane protein
-transmembrane proteins span both the cytosol and ER lumen sides
-have a hydrophopic stop sequence, hydrophilic end (cytosol site, interact w aq)
-RNA conerted to protein in cytosolic ribosomes, co-translational translocation
-signal sequence (N-terminus end) attaches to translocator protein
-signal sequence cleaved by signal peptidase
-protein is fed into ER until translocator protein reaches stop-transfer sequence
-transmembrane protein has different orientation if signal sequence is internal:
-can have N-terminus of C-terminus facing cytosol
-Determined by AAs around signal sequence
-more positive AA side faces cytosol, negative side faces ER lumen
*path of multipass transmembrane protein
-co-translational tranlocation, N/C-termius both face one side, depends on charge
-start and stop sequence both embedded in ER membrane Ppt26
*both star and stop transfers are hydrophobic.
*the translocator open laterally and 내보내 the protein
*start—is active, targeted to a specific translocator
•The Golgi apparatus receives proteins and lipids from the endoplasmic reticulum, modifies
them(glycosylation), and then dispatches them to other destinations in the cell by vesicular form.
*golgi is a stack of cisterna
Protein bud off from ER, fuse w cis golgi, then move through individual cisterna by
budding of and fusing to trans cisterna.
The reason for this is: glycosylation is complex, it requires several enzymes
-Actually starts in the ER: A single type of oligosaccharide is attached to many proteins.
-Complex oligosaccharide processing required for mature proteins occurs in the Golgi
*golgi: multi stage processing unit, different enzymes located at different cisterna
-it’s hard to study a specific glycosylation Ppt31
[Maintenance of membrane protein asymmetry]
(the direction of proteins ex) toward lumen, toward extracellular)
-Each protein is inserted into the membrane in the ER in a specific manner
This is the result of ―membrane insertion‖
-This protein asymmetry is maintained through vesicular transport
[Recap: Sorting of a PM protein.]
•Translation starts on cytosolic ribosomes.
•Signal sequence directs the protein to the ER.
•There are different ways the protein can be inserted into the membrane.
•The signal sequence is: hydrophobic
•This is: Co-translational translocation to ER
•Protein inserted through the membrane by a:
•Protein moves in transport vesicles to the PM
•Vesicle membrane fuses with the PM during Ppt33
*Endosome: membrane-bound organelle that carries materials newly ingested by endocytosis and
passes them to lysosomes for degradation.
*Lysosome: a small sac of digestive enzymes that functions in degrading worn-out organelles, as
well as macromolecules and particles taken into the cell by endocytosis.
-endosome and lysosome are temporaly liked doing same function,,BUT can be identified
*Endocytosed material found in the early endosome.
*Lysosomal proteins are delivered in vesicles from the Golgi