08_Endomembrane System Flashcards
What organelles are included in the endomembrane system?
ER, Golgi complexes, endosomes, lysosomes, secretory vesicles
Is the endomembrane system present in prokaryotes?
no
What is the interior of each compartment along the endomembrane system termed? (Space between the lipid bilayer)
lumen
What is the topology of the lumen similar to?
cell exterior
What are membrane contact sites?
The are close appositions between two organelles that facilitate signalling and passage of ions & lipids from one cellular compartment to another.
At MCSs, membranes are close, but they do NOT fuse.
Which eukaryotic organelle has MCSs with all other organelles?
ER
What are cisternae?
stacks of flattened membrane atop each other
Ribosomes are on the (cytosolic/lumen) surface of the RER.
cytosolic
What is the ER surrounding the nuclear envelope called?
perinuclear ER
What proportion of proteins are synthesized on ribosomes of the RER?
2/3
Which types of proteins are synthesized on ribosomes of RER?
secreted proteins
integral membrane proteins
soluble proteins of organelles (e.g. for lysosomes)
Where are nuclear proteins synthesized?
in the cytosol, on free ribosomes
Where are secreted proteins synthesized?
ribosomes on RER
Where are peripheral membrane proteins synthesized? How about integral membrane proteins?
peripheral: free ribosomes in cytosol
integral: ribosomes on RER
Which types of proteins are synthesized on free ribosomes in the cytosol?
cytosolic proteins
peripheral membrane proteins
nuclear proteins
proteins incorporated into chloroplasts, mitochondria, and peroxisomes
What determines where a particular protein will be synthesized?
the signal sequence –> if present, synthesis on ribosome in RER
What is a signal sequence?
a sequence of amino acid residues in the N-terminus of the nascent peptides that are to be secreted or that are integral membrane proteins
What does a polypeptide pass through in order to enter the ER lumen?
protein-lined pore
What would happen if the signal sequence of a secreted protein was to be removed?
it wouldn’t be secreted, and would stay in the cytosol
What protein recognizes a signal sequence?
What type of protein is this?
signal recognition particle (SRP)
G-protein
What do the SRP and ribosome bind to in the process of binding of the complex to RER?
SRP –> SRP receptor
ribosome –> translocon
What is the energy from the GTPase activity of the SRP and SRP receptor used for?
binding of the ribosome to the translocon and release of SRP
What causes the opening of the translocon plug?
Once the SRP is removed, translation continues and the signal sequence inserts into the translocon channel. There, it binds the interior and this interaction the plug to move and the channel to open.
Where is the signal sequence cleaved? What enzyme achieves this?
in the RER lumen; signal peptidase
