Protein Synthesis pt. 3 Flashcards
Does the synthesis of all proteins begin on cytoplasmic ribosomes?
Yes
Which types of proteins complete synthesis on ER bound ribosomes?
Membrane
Secretory
and Lysosomal proteins
What determines the site of protein localization?
Signal contained in the primary structure of the protein.
What signal targets a protein for the nucleus?
Lys-Lys-Lys-Arg-Lys
What signal targets a protein for the membrane and/or secretion?
20-30 AA signal sequence with a string of hydrophobic AAs.
What signal targets a protein to the lysosome?
Mannose-6-phosphate
What protein binds to the secretory, membrane, and lysosomal proteins during translation to target them to the rough ER.
SRP. Signal recognition protein.
Where do proteins go as they are synthesized on the rough ER ribosomes?
They are translated INTO the lumen of the ER via a channel called Sec61.
How do membrane-spanning proteins get translated?
Translocated to rough ER to make the bit inside the ER lumen until a stop transfer sequence (about 50% through) is reached causing the remainder of the protein to be translated in the cytosol.
Where does glycosylation of asparagine occur?
ER
What does peptidyl prolyl isomerase do?
Helps fold proline-rich regions
What does protein disulfide isomerase do?
Promotes native conformation of disulfide bonds
What is O-linked glycosylation and where does it happen?
Glycosylation of Ser/Thr residues that occurs in the golgi apparatus
How is M6P added in the cis golgi to target lysosomal proteins?
Mannose + phosphorylated sugar
then subtract sugar
Fabry’s disease is caused by a defect in what?
alpha-galactosidase A resulting in misfolded globosides which then accumulate in lysosomes.
