Lysosomes and Endosomes Flashcards
What is the name for the ‘digestive’ organelle in eukaryotes?
Lysosomes
True or False: lysosomes can only degrade small proteins and lipids.
False. They degrade all sorts of macro molecules and organelles.
What happens to the leftover products of degradation from the lysosome?
They are transported to the cytosol and reused.
What role do ATPase proton pumps play in lysosome degradation?
It maintains the low pH needed for lysosomes to function by pumping H+.
True or False: lysosomal proteins are O-glycosylated.
False. They are N-glycosylated, and thus start the process from the ER.
What is the purpose of a mannose-6-phosphate (M6P) on a protein?
It acts as a lysosomal targeting signal when it is transported from the trans Golgi network
True or False: M6P-bearing lysosomal proteins are transported in clathrin-coated vesicles.
True.
Vesicles need what type of protein in order to be coated in clathrin?
GGA adaptor coat proteins.
Name the protein that mediates recruitment of GGA adaptors to the TGN.
Arf1-GTP. It acts similarly to Sar1-GTP.
What is the structure of clathrin?
A molecule consisting of 3 light chain polypeptides and 3 heavy chain polypeptides. They combine to form a 3 legged structure (triskelions).
Clathrin transitioning from a hexagon to a pentagon serves what purpose in vesicle formation?
It acts as the driving force for the membrane to curve when forming the vesicle.
True or False: dynamin pinches off clathrin-coated vesicles.
True. It’s a GTP-binding protein that surrounds the stalk. GTP hydrolysis pinches off the vesicle.
What happens to the clathrin coat after pinching off of a vesicle?
It disassembles into the cytosol and returns to the TGN for another vesicle.
True or False: a clathrin-coated vesicle must first fuse with an endosome before getting ‘eaten’ by lysosomes.
True. The material from the late endosome will be consumed by the lysosome along with the cargo.
True or False: M6P receptors are ‘eaten’ by lysosomes along with the endosome.
False. They are recycled in order to be used for another round of trafficking.
Name the two processes for materials to enter a cell.
Endocytosis (selective internalization) and Phagocytosis (cellular eating)
What is another name for pinocytosis?
Bulk-phase endocytosis or cellular drinking.
Which type of adaptor protein is required for clathrin coating on vesicles undergoing endocytosis?
AP2 adaptors. They work similarly to GGA adaptors.
What is the role of an early endosome?
To sort and recycle extra-cellular materials via endocytosis.
What happens to receptors that early endosomes recycle?
They are carried by vesicles back to the plasma membrane.
What happens to any non-recyclable material in the early endosome?
A compartment detaches and matures into a late endosome. Fragments (MVBs) are then eaten by the lysosomes.
