Vesicular Targeting, Lysosomes & Endosomes (15) Flashcards
what facilitates movement of vesicles?
microtubules & motor PROs
when does the vesicle attach to motor PROs?
when the coat is shed, there is a PRO on the vesicle enabling motor PRO attachment
Rab PRO
integral membrane PRO
GTP binding PRO
direct vesicles to where they need to go in the cell & then tethering PROs attach to Rabs bringing them closer to the target membrane
T-SNARE
located on the receiving/target membrane (diff ones on diff target membranes)
V-SNARE
located on the vesicle, type of V-SNARE is determined by the type of COP PRO on the vesicle
SNARE PROs
family of diff PROs each with a diff location/target
when are V-SNAREs incorporated in the vesicle?
incorporated in the membrane during budding
docking
T-SNARE on the receiving membrane has an affinity for the V-SNAREon the vesicle
how do vesicles fuse with their target membranes?
SNARE PROs intertwine & pull membranes together allowing them to fuse
nerve cells membrane fusion
nerve cells releasing neurotransmitters synaptic vesicle dock to presynaptic membrane in nerve cells
vesicles are dumped & fuse with postsynaptic membrane (neuron, muscle etc.)
what happens to SNARES once the vesicle has fused?
recycled through interactions with COP I
when do V & T SNARES interact?
during tethering
what do lysosomes breakdown?
organic substances: NAs PROs GAGs (glycosaminoglycans) Glycogen Oligosaccharides Sphingolipids Phospholipids Triglycerides
what happens to the compounds that lysosomes breakdown?
various transporters dump subunits into the cytoplasm to be reused
PROs (enzymes) destined for the lysosome are tagged with ____
phosphorylated mannose (6) residues
what is the role of clathrin?
Coat PRO, clathrin facilitates the vesicles budding from the Golgi which then travel to a phagosome or other vesicle, clathrin will shed facilitating fusion (primary lysosome)
primary lysosome
Non-functional lysosome, enzymes haven’t been activated
secondary lysosome
enzymes are activated & are capable of hydrolysis
what does the lysosomal membrane contain?
Proton pump maintaining the pH inside by pumping protons inside
2 groups of acidic, highly glycosylated PROs line the interior protecting the inner lining from the enclosed enzymes
When do lysosomal enzymes have optimal activity?
at an acidic pH
heterophagy
degradation of foreign material brought into the cell by phagocytosis
Primary lysosome fuses with the phagosome & digests the contents
Introduce the enzymes converting it into a secondary lysosome
what are purposes of heterophagy?
nutrition: products move into the cytoplasm
defense: microorganisms are killed
what type of cell acts as a defense mechanism in heterophagy?
white blood cells destroying microbes
phagolysosome
lysosome + phagosome
autophagy
digestion of intracellular components that have damage or no longer needed
Isolation envelope forms around components, fuses with primary lysosome, dump enzymes, lower the pH & contents are degraded
autophagolysosome
lysosome + autophagic vacuole
autolysis
rupture of lysosome within cytoplasm kills the cell
when does autolysis occur?
when infection cannot be resolved
programmed cell death during development, ex: selective removal of cells removing webbing b/w fingers & toes
extracellular digestion
lysosomes may discharge their enzymes to the outside of a cell by exocytosis
when does extracellular digestion occur?
acrosome in sperm fertilization
sperm will hit the egg, release lyssomes with digestive enzymes allowing the sperm to enter the egg & fuse with the membrane& fertilize
how do phagocytosed bacteria escape destruction?
Fusion of primary & phagosome is inhibited
Bacterium prevent proton pumps from working, pH is not where it needs to be & enzymes are unable to perform their function
Bacteria escape secondary lysosome by producing phospholipase to destroy lysosomal membrane (lysosome bursts and bacteria move out)
What are ways that lysosomes fail to carry out their functions?
Phagocytosed bacteria escape
Lysosome with a missing acid hydrolase
what occurs in lysosomes with a missing acid hydrolase?
Lysosomes don’t have necessary enzymes to break down the materials so they accumulate
endocytosis
cellular uptake of particles & macromolecules
what are the types of endocytosis?
Phagocytosis: uptake of particulate matter
Bulk phase (pinocytosis): cell drinking, uptake of extracellular fluids without recognition by surface of PM Brings anything in that’s around the area where endocytosis occurs
Receptor-mediated endocytosis: uptake of specific macromolecules
Brought to endosomes
what are professional phagocytes in phagocytosis?
macrophages
neutrophils
how do lysosomes kill ingested microbes?
Contain lysozyme, an enzyme that degrades bacterial cell walls
Acidic pH kills some bacteria alone
Oxidases on inner surface of phagosome produce hydrogen peroxide that kills some bacteria
what type of endocytosis has coat PROs?
receptor-mediated
early endosomes
located near the periphery of the cell, aggregation of endocytotic vesicles
late endosome
interior of the cell, sort materials & send them off to fuse with a primary lysosome (activating the secondary lysosome
where do late endosomes receive material from?
Receive materials from: early endosomes & Golgi
what type of endosome can develope into lysosomes?
late endosome
coated pits
sites on membrane where receptors for receptor-mediated endocytosis are concentrated
coated with clathrin PRO (on the cytoplasmic side)
what are the steps in the endocytosis pathway?
- Clathrin coat is removed from coated vesicle to yield uncoated vesicle
Strips receptors & sending them back to be recycled - Uncoated vesicle fuses with early endosome
- Transport or carrier vesicle buds off from early endosome
- Transport vesicle fuses with late endosome
- Transport vesicle bud off from late endosome & contain either:
a. Ligand only
b. Receptor only
c. Receptor ligand complex
How do endosomes deal with receptors & ligands? (4)
Receptor returned to PM & ligand delivered to lysosome for degradation
Nutrition
Both receptor & ligand returned to PM where ligand is released
Both receptor & ligand are destroyed in a lysosome
Receptor & ligand delivered to opp side of cell & ligand released into extracellular space
Transcytosis
Transcytosis
where receptor & ligand are taken in from one side & sent out the other
when does transcytosis occur in humans?
Infant’s intestines take up antibodies from mom’s milk. The infant takes the antibodies in with receptors & prevents digestion by sending them out the other side
