mod 4 Flashcards
what are the components of the endomembrane system?
ER, golgi , endosomes and lysosomes (NOT perosixomes)
Cotranslational import
peptide moves across the ER to remain or is transported by vesicles to endomembrane system (ribosome on ER)
posttranslational import
peptides for cytosol or nucleus, mito, chloroplasts, or peroxisomes move via postranslational (free ribosomes)
first 3 steps of the signal mechanism
- signal recognition particle binds to er’s signal sequence and ribosomal subunit stopping translation
- SRP and SRP receptor binds and the ribosome and the translocon
- the SRP’s bind a GTP each so pore opens and polypeptide is inserted
4-6 steps of signal mechanism
- GTP hydroylsis releases the SRP
- signal sequence is cleaved by signal peptidase
- polypeptide is released in the ER lumen, ribosome is releaseed and translocon pore closes
occurs with internal stop transfer sequence and a terminal ER sequence
the stop of the protein halts the translocation and moves to the side in the translocon to anchor the polypeptide so the N-terminus is in the ER lumen and the C-terminus in the cytosol.
occurs w single internal start transfer sequence
the polypeptide loops straight thru the channel starting at the sequence
N-glycosylation
proteins made at RER cotranslationally by oligosaccharyltransferase (protein complex), they are added to an ASN. Has a nitrogen in the link.
where is drug detoxification?
the smooth ER in liver cells, hydroxylation is the first step, the p450 in the liver plays huge role
functions of the smooth ER
lipid metabolism, detoxification, caro metabolism, calcium storage, steroid biosynthesis.
where are most phospholipids and cholesterol are made ?
on the cytosolic face of ER
specifications of lipid biosynthesis
flippases (double membrane), even distribution and asymmetry.
Golgi faces, and 2 models of formation
cis- oriented towards ER and trans- face away.
1. stationary cisternae model and cisternal maturation model
membrane incresaes in thickness from 5 to 8nm
Anterograde and retrograde transport
anter- ER - golgi - plasma mem.
retro- vesicles from golgi- ER
N-linked glycosylation
starts in ER, folds the proteins, and modifies the N-glycosyl group, attaches to serine or threonine.
what could keep proteins retained?
kin recognition (cluster to avoid going in vesicles), retention tags keep them in ER ( receptors bind to tags), and retrievel tags, KDEL and KKXX
Constitutive secreation and regulated
always on, default pathway, unregulated
regulated- vesicles fuse w mem. w a specific signal, and bud from TGN
what is receptor mediated encodytosis
also clathrin dependent endocytosis, need receptors on outer membrane. can hold about 1000 receptors, more than 2 different receptors have been identified
low density receptor mediated endocytosis
holds cholesterol
caveosomes
lipid rafts
all the coat proteins
Clathrin: PS to endosomes
COPI: golgi to ER
COPII: PS to ER
clathrin coat
initiated by ARF (GTpase) , dynamin pinches off the coat
dynamin
binding domain and GTPase domain
COPI and COPII coat
COPI: initiated by ARF protein
COPII: initiation of Sar1
