Lecture 14: Vesicular Trafficking 2 Flashcards
Lysosomes require ____ environment and ____ cleavage for optimal activation
acidic, proteolytic
_____ pump H+ into lysosomes to maintain the acidic pH and to drive transport of small metabolites
Vacuolar ATPases
Lysomsomes contain about 40 types of enzymes such as
- Proteases, nucleases, glycosidases, lipases, phospholipases, phosphatases, and sulfatases
an early endosome becomes a late endome after
microtubul-mediated transport
a late endosomes can fuse with lysosomes to become
endolysosomes
early endosomes come from
plasma membrane and trans golgi network
Lysosomal hydrolases have the sorting signal ____ attached to them in the CGN
mannose-6-phosphate (M6P)
M6P receptors in ____ recognize the sugar. the recepotrs bind hydrolases and to adaptor proteins in assembling clathrin coats. Packaged into ______ that bud from ____
- Trans Golgi Network (TGN)
- Clathrin-coated vesicles that bud form TGN
_____ recognizes lysosomal hydrolases in the Golgi apparatus
GlcNAc phosphotransferase
Lysosomal Storage Diseases
- Genetic defects in lysosomal hydrolases
- Leads to accumulation of undigested material in lysosomes
- Ex
- Hurler’s disease
- mutation in the enzyme required to break down glycosaminoglycan chains
- Inclusion Disease
- all the lysosomal hydrolases are missing in many cell types. Undigested substrates accumulate as “inclusions”
- Defective or missing GlcNAc phosphotransferase (this is a major cause of inclusion-cell disease)
- GlcNAc phosphotransferase is an enzyme that adds M6P to lysosomal hydrolases. The enzymes are not phosphorylated and hence not sorted into vesicles and not delivered into lysosomes
- instead they are carried to cell surface and secreted (thus found in blood)
- Hurler’s disease
Large particles ingested by vesicles are called ____
phagosomes (phagocytosis)
Small particles ingested by pinocytic vesicles a process called
pinocytosis
The conversion of early endosomes ot late endosomes is accompanied by loss of the _______
tubular projections
what is the best example of receptor-mediated endocytosis
Cholesterol uptake
Receptor-mediated Endocytosis
- used ot import select macromolecules from outside cell
- Molecules bind ot receptors on membrane surface
- Accumulate in clathrin-coated pits
- enter cell as receptor-macromolecular complex in clathrin-coated vesciles
- Provides selective concentration mechanisms
- (blockage of this pathway leads to atherosclerosis)
Blockage of receptor mediated Endocytosis leads to
Atherosclerosis
The sequestration of endocytosed proteins into intralumenal vesicles of multivesicular bodies is done how?
- Ubiquitylated membrane proteins are sorted into domain on the endosome memebrane, which invaginate and pinch off to form intralumenal vesicles. The ubiquitin marker is removed and returned to the cytosol for reuse before the intralumenal vesicle closes.
Possible fates for transmembrane receptor proteins that have been endocytosed
- Retrieved receptors are returned to the same plasma membrane domain form which they came (recycling) or via a recycling endosome to a different domain of the plasma memebrane (transcytosis)
- Receptors that are not specifically retrieved from early or recycling endomes follow the pathway form the endosomal compartment to lysosomes, where they are degraded (degradation)
Recycling endosomes can serve as an _____ site for specialized plasma membrane proteins that can be mobilized when needed. Ex?
- intracellular storage site
- ex. Insulin binding to insulin receptor triggers an intracellular signaling pathway that causes the rapid insertion of glucose transporters into the plasma membrane of a fat or muscle cell, greatly increasing its glucose intake
Examples of phagocytes
Macrophages and Neutrophils
Antiboides bind to microbe, Fc chain recognized by Fc receptor on surface of macrophages/neutrophils triggers formation of _____ which engulfs the particle and forms a ____
- Pseudopod
- Phagosome
Pseudopod formation is driven by localized _____ and _____ and is controlled by
- actin polymerization and reorganization
- and is controlled by Rho GTases and Phosphoinositide signaling (PI (4,5)P2 stimulates actin polymerization, which promotes pseudopod formation, and then PI (3,4,5)P3 depolymerizes actin filaments at the base.
Pinocytosis or ‘cell drinking’ is a constitutive process and occurs continuously in all eukaryotic cells. cells ingest bits of the ____ in the form of small pinocytic vesicles
Plasma membrane (macrophages ingest about 3% of its membrane every minute)
The process of pinocytosis begins at _______
clathrin-coated pits
