Protein trafficking 1 Flashcards
(40 cards)
What must cells control to function effectively?
Localization of proteins.
Where are digestive enzymes and insulin secreted in the pancreas?
Enzymes into the pancreatic duct; insulin into the bloodstream.
Where must insulin receptors be located?
In the plasma membrane.
Where does most protein synthesis occur?
In the cytoplasm.
What determines where a protein ends up in the cell?
Organelle-specific targeting signals.
What are microsomes?
ER-derived membrane spheres without ribosomes.
What do microsome studies show?
That translation and ER import must occur simultaneously.
What is the function of the signal peptide?
Directs the protein to the ER via the SRP.
What is the SRP?
A complex of six proteins and one non-coding RNA.
What does the SRP54 subunit do?
Binds the signal peptide and ribosome subunits.
What is the role of the translocon?
Moves the growing peptide into the ER lumen.
What proteins make up the translocon?
Sec61α, β, and γ.
What happens to the signal peptide in the ER?
It is cleaved by signal peptidase.
When does protein folding begin?
Once the protein is in the ER lumen.
What characterizes type I membrane proteins?
N-terminus in the lumen, presence of a signal peptide.
What halts translocation in type I proteins?
A stop-transfer anchor sequence in the TM domain.
What is meant by membrane protein topology?
Number of TM domains and orientation of N- and C-termini.
What is unique about type II membrane proteins?
Internal signal anchor, C-terminus in the lumen.
What distinguishes type IV TM proteins?
Multiple TM domains with alternating orientation.
How are tail-anchored proteins inserted into membranes?
Via Get3 and the Get1/Get2 receptors.
What are GPI anchors?
Amphipathic membrane anchors added after TM domain cleavage.
What do GPI anchors regulate?
Protein mobility and localization in membranes.
What is common for extracellular proteins?
Glycosylation.
What is N-linked glycosylation?
Carbohydrates bind to the sidechain amino group of asparagine.
