Lecture 18 Flashcards
What do proteases, nucleases, glycosidases, lipases, phopholipases, phosphatases, and sulfatases all have in common?
they are all different types of lysozomes (acid hydrolases)
Describe the conditions for optimal activation of a lysosome.
an acidic environment and proteolytic cleavage
What is vacuolar ATPase pumps on lysosomes?
They pump H+ into lysosomes in order to maintain the acidic pH within their membrane and to drive the transport of small metabolites across the lysosomal membrane
True or false
lysosomes are homogenous
False
they are heterogenous and derived from late endosomes
Explain the role of late endosomes and endolysosomes when it comes to the maturation process of a lysosome
late endosomes fuse with prexisting endolysosomes or lysosomes (after the digestion of their contents by hydrolase) to form a mature lysosome.
List the 3 “lines of trafficking” that eventually end up fusing with lysosomes
Phagocytosis forming phagosomes
Endocytosis forming late endosomes
Autophagy forming autosomes
Describe autophagy. what type of trafficking vesicle is formed during autophagy?
means “self eating” and occurs via the formation of vesicular bodies within the cell
these vesicular bodies merge with one another and engulf the organelle/material that is destined for lysosomal digestion into an “autophagosome”
Describe how membrane proteins and hydrolases are transported to lysosomes.
lysosomal enzymes are co-transitionally transported into the rough ER, then to the golgi network (leave via the TGN), and then bud off into endosomes
How are lysosomal proteins sorted?
Lysosomal hydrolases have mannose-6-phosphate (M6P) added to them in the CGN
The receptors in the TGN recognize the M6P sugar, a phosphate is added, and they are packaged into clathrin coated vesicles, headed for mature lysosomes
during the synthesis of lysosome precursor enzymes, what all is added in the CGN?
P-GlcNAc and M6P sugar (which is uncovered in the TGN)
once a transport vesicle fuses with a mature lysosome, what happens?
a phosphate is removed from the complex and the lysosomal hydrolase precursor dissociates from the M6P receptor due to the high pH
after delivering the hydrolase to a lysosome, what happens to M6P receptors?
they are sent back to the golgi in a “receptor retrieval” vesicle
How is the UDP-GlcNAc added to a lysosomal hydrolase? where/how is it added?
GlcNAc phosphotransferase adds the UDP-GlcNAc to the N-linked oligosaccharide (which has a terminal M6P residue)
UMP is lost during the first step of this process
After a lysosomal hydrolase is released from GlnNAc phosphotransferase, what happens?
GlcNAc is removed
describe GlcNAc phosphotransferase in terms of it’s sites
it has a catalytic site where it adds UDP-GlcNAc to the lysosomal hydrolase
it has ha recognition site that recognizes the signal patch of a lysosomal hydrolase
generally describe lysosomal storage diseases
they are genetic defects in lysosomal hydrolases that cause the accumulation of undigested material in lysosomes
List 2 lysosomal storage diseases and describe them
Hurler’s disease: mutation in the enzyme required to breakdown glycoaminoglycans
Inclusion cell disease: all of the lysosomal hydrolases are missing and undigested substrates accumulate as “inclusions”
What happens there is a defective/missing GlcNAc phosphotransferase?
M6P is not added to lysosomal hydrolases which causes enzymes not getting phosphorylated
Without being phosphorylated they are not sorted into vesicles and trafficked to lysosomes
What is endocytosis? what are the 2 types of endocytosis?
the uptake of macromolecules form the exterior of the cell
Phagocytosis and pinocytosis
describe the relationship between endolysosomes and lysosomes
existing lysosomes fuse with endolysosomes in order to create more mature lysosomes. this process occurs repeatedly
What is the main difference between phagocytosis and pinocytosis?
the size of the particle(s) being endocytosed
large=phagocytosis
small=pinocytosis
Describe the process of receptor-mediated endocytosis.
select molecules bind to receptors on the outside of the membrane and accumulate in clathrin coated pits
give an example of receptor-mediated endocytosis and what happens when this pathway is blocked.
cholesterol uptake is an example
atherosclerosis occurs if this pathway is blocked
describe how receptor-mediated endocytosis yields free cholesterol on the inside of the cell
LDL’s bind to receptors on the outside of the membrane and accumulate in clathrin-coated pits
these form coated vesicles that fuse with early endosomes, destines for lysosomes
hydrolytic enzymes digest the LDL into free cholesterol and receptors in the endosome return to the PM
