ER, Vesicular Transport, Cotranslational Import Flashcards
what is the function of the rough er
protein synthesis, modification, and transport
synthesis of membrane phospholipids
glycosylation of proteins
addiction of carbohydrate chains
where does protein translation begin
on free ribosomes
what are the two ways protein translation happens
1) completed on free ribosomes
2) completed by ribosomes associated with rough er
describe protein translation that’s completed on free ribosomes
- cytosolic proteins
- peripheral membrane proteins
- proteins are targeted to the nucleus, mitochondria, peroxisomes, and chloroplasts
where are cytosolic proteins translated
free ribosomes
where are peripheral membrane proteins translated
free ribosomes
where are the proteins translated at free ribosomes targeted to
nucleus, mitochondria, peroxisomes, chloroplasts
describe protein translation that occurs on ribosomes associated with the rough er
- secretory proteins
- integral membrane proteins
- soluble proteins associated with inside (lumen) of the endomembrane system (ie proteins that fuction within the er, Golgi, and lysosomes)
where are secretory proteins translated
ribosomes on rough er
where are integral membrane proteins translated
ribosomes on rough er
where are pertains that function in the endomembrane system (the er, golgi, lysosomes) translated
ribosomes on rough er
how is the site of translation determined
they are targeted by a signal sequence
where is the signal sequence located
proteins contain the signal sequence which determines where they are translated
where on proteins is the signal sequence located
located on its amino-terminus
what does the signal sequence contain
the signal sequence contains several consecutive hydrophobic amino acids
what does the signal sequence do
the signal sequence directs synthesis to ER
how does the signal sequence work
proteins move through a channel into ER
what is another term for the process that comes after the signal sequence
cotranslational import
what terminus comes out of the ribosome first
the N-terminus comes out first (because it goes in first)
what terminus goes in ribosome first
the N-terminus
describe the four steps of cotranslational protein import
1) signal recognition particle
2) targeting of translation complex to er
3) SRP is released and ribosome binds to the translocon
4) polypeptide enters the ER and is translated
describe the first step of cotranslational protein import
1) signal recognition particle
the signal recognition particle (SRP) binds to the signal sequence, and translation STOPS
describe the second step of cotranslational protein import
2) targeting of translation complex to ER
SRP/RIBOSOME +MRNA/NEW POLYPEPTIDE
describe the third step if cotranslational import
3) SRP is released and ribosome binds to the translocon
- protein synthesis resumes
describe the fourth step of cotranslational import
4) polypeptide enters the ER (through traslocon) and is translated
- signal sequence is cleaved off
- chaperone folds protein
what are the two options a protein targeted to the ER lumen (after it is finally synthesized and folded) has?
1) is retained in the ER lumen (if that’s where it functions)
2) is transported from the ER to the Golgi complex for further modification and is delivered to distal parts of the biosynthetic/secretory pathway. (final destination could be outside of the cell)
once in the ER, a protein is now part of the ________, and may ultimately become a part of a compartment, or be secreted
once in th ER, a protein is now part of the biosynthetic/secretory endomembrane system and may ultimately become a part of a compartment, or be secreted
example fo a 12 pass protein
CFTR
odd number pass protein will end up:
on the oposite side of the membrane as it started
even number pass protein will end up:
on the same side of the membrane as it started
