1What are the 2 types of proteins that are signaled to enter the ER?
Transmembrane proteins and Water-soluble proteins.
2Describe TP
Synthesized in lumen and partly translocated, embedded into the membrane. Destined to stay in ER or plasma membrane proteins.
3Describe Water soluble proteins
Translocated into the ER lumen and are desitined for lumen of organelle or secretion.
4Explain cotranslational translocation:
When the growing polypeptide is simultaneously translated by mRNA, it is translocated across the ER membrane.
5Explain post-translational translocation:
When the polypeptide is translated by mRNA first and then translocated across the membrane. Needs chaperone proteins in the cytosolic side of ER.
6Major role of Rough ER
Protein synthesis, has membrane bound ribosomes.
7Major role of Smooth ER
Produces lipids and steroids and cholesterol (contains cytochrome p450 family, makes water insoluble drugs soluble which are then excreted).
8What is GPI
A method of anchoring proteins to the ER membrane. GPI is the anchor covalently bonded to the c terminus of a protein destined to be attached to the plasma membrane.
9What determines a Protein as a ER resident?
Retention signal near C terminus
10What is PDI?
PDI is protein disulfide isomerase, Catalyzes the oxidation of free sulfhydryl groups on cysteines to form disulfide groups. A kind of ER resident protein.
11What is BIP?
Chaperone protein that recognizes incorrectly folded proteins.
12What are glycosated proteins destined for?
Golgi, lysosomes, membrane proteins, extracellular space.
13Ogliosaccharides are said to be _____
Nlinked
14What synthesizes ogliosaccharides?
Rough ER will synthesize the oligosaccharides on the cytosolic side, when synthesis of oligosaccharides occurs they add phosphate groups. During the synthesis process, the oligosaccharides are flipped to the lumenal side of the ER.
15What is ogliosaccharide made up of?
Ogliosaccharide chain is connected to ER membrane via a dolichol with a strong phosphate group. (phosphates are high in energy and needed for transfer to proteins)
16Explain Glycosations:
Translocating protein on the cytosolic side of cell will dock at a oligosaccharyl transferase. The active site of OT is on the lumenal side of ER. The ogliosaccharide chain is transferred to cytosolic side and attached to asparaginine of translocated protein.
17What was the signal hypothesis?
The signal or n terminus signal sequence of the translocated proteins is cleaved off by a peptidase embedded in the Rough ER membrane.
18How does a protein/polypeptide get translocated across the Rough ER membrane?
While the protein/polypeptide chain is being translated it has a signal sequence that binds to signal recognition particle.
The SRP binds to a SRP receptor embedded in the Rough ER membrane and opens the translocator.
The polypeptide chain enters while being translated and has its N terminus cleaved by the RER peptidase.