proteins and vesicular transport Flashcards
Where do proteins synthesised by ribosomes in the cytosol go?
- remain in cytosol
- go to mitochondria, peroxisomes, nucleus
Where to proteins made at the ribosomes at the ER go?
- for secretion
- plasma membrane
- lysosomes
How do cells know the correct location for a protein?
- part of the amino acid sequence contains a signal sequence
- proteins without a signal sequence remain in the cytosol
When do proteins need to be unfolded?
when they are transported across or into membranes
When do proteins get to remain folded?
- when transported through pores or by vesicles
What are nuclear pores made of?
complex of around 30 different proteins called nucleoporins
What does importin do?
- recognises nuclear localisation signal (NLS)
- carries protein into nucleus
How does importin carry proteins into the nucleus?
disrupts gel-like mesh of the proteins lining the channel
How does importin release the protein and return back to the cytosolic side of the pore?
- interacts with Ran
How do ribosomes bind to the ER?
- signal recognition particle (SRP) binds to signal sequence on ribosome
- SRP binds to receptor on ER and gets released
- ribosome passes to protein translocator which binds the signal sequence
How are proteins glycosylated?
- appropriate asparagine (Asn) enters ER lumen
- it is glycosylated by covalent addition of branched oligosaccharide side chain
Which proteins are usually glycosylated?
- during transport to the ER they often are
- most cytosolic proteins are not
What is the unfolded protein response (UPR)
- when there is an excess of unfolded proteins in the ER
- sensor proteins activate and stimulate expansion of the ER, more chaperones and less new proteins entering ER
Where are endocytosed vesicles usually delivered to?
- to early endosomes
- then to lysosomes via late endosome
What is the constitutive pathway of exocytosis?
- continual secretion of soluble proteins from cell
- this route replaces proteins and lipids in membrane
