Protein Trafficking Flashcards
(26 cards)
endocytosis …
IN
exocytosis …
OUT
non secretory pathways
- if protein lacks ER signal, translation is completed on free ribosomes in cytosol
- if protein has organelle-specific signalling sequence, then generated in cytosol + targeted to functional site
secretory pathways
- proteins that = secreted = generated on cytosolic ribosomes + target ribosome to ER
- translation completed on RER
- secretory proteins pass through Golgi complex via transport vesicles
- Golgi sorts proteins to plasma memb / to lysozymes
what are the reasons for secretion?
- digestive enzymes
- extracellular matrix
- cell to cell signalling
what are the 3 basic steps in protein secretion?
- protein synthesis + translocation across ER membrane
- protein folding + modification inside ER lumen
- protein transport to golgi, lysosomes/cell surface through budding/fusing of vesicles
describe co-translational translocation?
- signal sequence on mRNA translated
- signal sequence bound by SRP
- SRP targets ribosome to SRP-receptor on ER membrane
- opening of translocation allows insertion of signal sequence + growing of PPC
- PPC passes through translocon + signal sequence cleaved by membrane bound peptidase
- signal sequence degraded in ER lumen
- polypeptide elongated in N terminal to C terminal direction
- ribosome released into cytosol from ER lumen
how do you insert proteins into membranes?
- ribosome attaches to translocon on ER membrane
- protein translated through translocon until hydrophobic stretch generated + membrane stop transfer anchor sequence found
- hydrophobic stretch = left in membrane
- translocon moves laterally + ejects protein
- rest of protein = generated
- complex dissociates
the secretory pathway is used to send proteins…
OUT of cell / to membranes
proteins only need to be translocated across a membrane ….
once
there are 3 types of vesicle,
what are they?
COPII - transport proteins from rough ER to golgi
COP I - transports proteins in retrogade direction between golgi and ER
Cathrin- coated - transport proteins from plasma membrane to endosomes
vesicle budding
- initiated by recruitment of small GTP-binding proteins to cell membrane —> invagination
- proteins coated in cytosol
- bind to cytosolic membrane cargo receptor proteins
- cargo proteins recruited into budding vesicle
- membranes fuse + vesicle = free
- coat proteins lost + recycled
what is SNARE?
SNAP (soluble NSF attachment receptor protein) receptor protein
what is NSF?
N-ethylmaleimide-sensitive factor enzyme - ATPase
vesicle docking
vesicle will fuse to target membrane via SNARE protein interaction
SNARE proteins are in pairs + ensure vesicle fuses with correct membrane
what is SNAP?
synaptosomal associated protein - allows specificity of vesicle docking
what is VAMP?
vesicle associated membrane protein
the retrieval of ER proteins from the golgi is carried out using the…
KDEL receptor
what protein complexes does an endocytic vesicle use?
- dynamin: GTPase
- clatherin - fibrous protein
what does dynamin do?
forms spinal around neck of vesicle
uses GTP hydrolysis
membrane and soluble secretory proteins are…
- glyocsylated (in ER + golgi)
- covalently stabilised by Cys-Cys bond formation (in ER)
- assembled into multi-subunit conformations (in ER)
- cleaved into active conformation (in ER, golgi, secretory vesicles)
in glycosylation, carbohydrates are added to proteins via the…
- carboxyl group of serine/threonine (O linked)
- amide nitrogen of asparagine (N linked)
where are disulfide bonds formed and reformed?
in ER lumen
describe Cys-Cys bonds?
- stabilise protein structure
- found in secretory/membrane bound proteins
