Week 9 - Protein Sorting and Modification Flashcards
(41 cards)
What happens to a transmembrane protein moving from cytosol to ER (overview)?
- Starts same as secreted proteins; mRNA codes
- Internal signal sequence recognized by SRP
- SRP binds ribosome to the SRP receptor at the ER membrane
4a. N-terminus surrounded by negatives; alpha helix joins membrane
4b. N-terminus surrounded by positives; alpha helix forms in receptor before joining membrane.
What happens to a transmembrane protein moving from ER to Golgi apparatus (overview)?
- Glycosylation of lipids and proteins; no flip-flopping.
What is the function of the Golgi apparatus?
Receives proteins and lipids from the ER, modifies them, and then dispatches them to other destinations in the cell. Complex oligosaccharide processing requires for mature proteins occurs here.
The closer the Golgi is to the ER…
The more interconnected the network is.
What is Protein Glycosylation?
The modification of proteins by adding/modifying sugar chains.
Where does Protein Glycosylation start?
It starts in the ER: a single type of oligosaccharide is attached to many proteins.
What is the Golgi apparatus?
A multi-stage processing unit; different enzymes in each cisterna. Complex oligosaccharide processing requires for mature proteins occurs in it.
How is the asymmetry of membrane proteins maintained during processing?
Each protein is inserted into the membrane of the ER in a specific manner; maintained through vesicular transport.
Define Endosome.
Membrane-bound organelle that carries materials newly ingested by endocytosis and passes them to lysosomes for degradation.
Define Lysosome.
A small sac of digestive enzymes that functions in degrading worn-out organelles, as well as macromolecules, and particles taken into the cell by endocytosis.
Endocytosed material is found where?
In the early endosome.
Lysosomal proteins are delivered in vesicles from the Golgi to what?
To the late endosome, for digestion of material.
What is phagocytosis?
A type of endocytosis; “cell eating”. A large particle is internalized.
A late endosome that has fully digested is called what?
A lysosome.
Early endosomes have a lot of enzymes but less what?
Less digestion than late endosomes.
Late endosomes digests more than an early endosome but still gets what?
Still gets more enzymes.
As a lysosome has a lot of digestive enzymes, it can be fused to what?
It can be fused to an early or late endosome to provide them with more enzymes.
What 2 mechanisms protect a cell from acid hydrolases?
- Acid hydrolases only function in acidic environments while the cytosol is neutral or basic
- Membrane permeability.
Lysosomes contains approx. 40 hydrolytic enzymes. What are the enzymes?
These enzymes are Acid hydrolases; they require an acidic environment.
Hydrolytic enzymes are named after what? (i.e. Nuclease).
They are named after what they cut; i.e. nucleases cut nucleotides.
What are lysosomes and endosomes acidified by?
They are acidified by a V-type ATPase; H+ pump.
What prevents contents of the cytosol from being digested by Lysosomes?
Lysosomal enzymes have a low pH requirement; won’t digest neutral or basic.
What protects lysosomal membrane proteins from proteases in the lumen?
Lysosomal membrane proteins are glycosylated for protection.
How do the products of lysosomal digestion get to the cytosol?
Transport proteins in the lysosomal membrane transfer the products out of the lysosome to the cytosol. (i.e. amino acids, sugars, nucleotides).
