Secretory and Endocytic Pathways Flashcards
Where are most secreted and membrane proteins made?
in the ribosomes of the rough ER
What happens to secreted and membrane proteins in the rough ER?
they are folded with the help of chaperone proteins and most are glycosylated - complex carbohydrates are attached to the proteins by ER enzymes.
What happens to proteins in the Golgi?
further modifications are made and additional quality control
What happens in the trans Golgi network?
proteins are sorted into carrier vesicles that go to different parts of the cell (endoscopes, lysosomes, secretory vesicles).
Constitutive secretory vesicles
automatically fuse with the plasma membrane
regulated secretory vesicles
fuse with the plasma membrane in response to a signal
Ex: vesicles containing hormones, neurotransmitters, blood clotting factors.
Where do integral versus secreted proteins live in the ER?
integral proteins including receptors and ion channels have 1+membrane-spanning domains in the lipid bilayer of the ER.
secreted proteins are aqueous in the lumens of the ER/golgi/secretory vesicles.
translocation in to the ER occurs in conjunction with which process?
translation of the protein/polypeptide
how does ER translocation work?
the N-terminus coming from the ribosome is marked with a signal sequence
- > signal is identified by signal recognition particle (SRP) and directs it to the preprotein translocase (halts translation)
- > polypeptide is threaded through the PPT as it elongates
- > goes into the ER and signal is removed by a protease and the protein folds.
How are transmembrane proteins placed in the ER membrane?
trans-membrane segments of the protein are released laterally into the membrane by pre protein translocase
What is the ER stress response?
signaling pathway that sense the amount of unfolded protein in the ER, slows down translation, and stimulates transcription of chaperone proteins
What happens when the ER stress response is overwhelmed?
cell may choose apoptosis
What happens to proteins that fail quality control checks in the Golgi?
they are transported back into the ER to attempt to fold correctly
What is the role of C-peptide and what is its clinical significance?
connecting peptide, or C-peptide, is a short 31-amino-acid polypeptide that connects insulin’s A-chain to its B-chain in the proinsulin molecule, and is later removed in the Golgi.
it is not degraded quickly - if measured you see integrated ability to secrete insulin over time (capacity of the pancreas to make and secrete insulin.)
coat complexes
assemble transport vesicles with specific contents - identify cargo lips and proteins and form a shell around them (budding of the plasma membrane)
