MCD BIO 165A Lecture 13: lecture 13 lysosomes & peroxisomes
10 Jan 2019
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lecture 13
lysosomes & peroxisomes
•
- Image of lysosome
➢ In dead cells: Immunostain for protein in lysosome; in live cells: tag with GFP
➢ This image: (uses neither of those 2) using dye (lysotracker) selective for
lysosomes; dye is everywhere else in the cell, but only fluorescing in lysosome
➢ dye takes advantage of lysosome property that makes it only fluoresce there
Lysosomes
• Dynamic organelles responsible for receiving and degrading macromolecules from the
secretory, endocytic, autophagic and phagocytic membrane trafficking pathways
- Garbage disposal, specialized to destroy things that are toxic, can accumulate
➢ Destroys protein in endomembrane system
- recycling amino acids, nucleotides, small molecules cell will be using again
• Discovery: fractionate cell -> which component degrades glucose 6 phosphate?
- Discovered Enzyme glucose 6 phosphatase in a fraction of cell associated with
membrane
- EM looking at that fraction of cell -> they’re lysosomes
Structure
• Heterogeneous appearance including acid hydrolases
• Wide size range: 25nm – 1um in diameter
- Because flux of degraded material differs in size
• Present in all EK cells with broad number of functions
• Lysosomal enzymes are a bunch of enzymes degrading stuff, e.g. phospholipase, acid
phosphatase, collagenase
• LDL is a protein lipid aggregate from diet; needs to be cleared from blood vessels
- Receptors on endothelial cells take them up thru endocytosis -> secretary pathway
thru endosomes; sorted so that receptor recycled back to cell surface, LDL shuttled to
lysosome to be destroyed -> provides breakdown products e.g. free cholesterol cell
can use (in this case, pathway important for clearing up LDL & prevent blood vessel
occlusion)
- After internalization: Cargo sorted in endosomes, those destined for degradation
sorted to lysosomes
- LDL taken up thru endocytosis -> secretary pathway into early endosome -> receptors
recycled back to surface, LDL transferred to lysosome & degraded
Origin
• Like most membranous organelles (except chloroplasts & mitochondria), membrane
originally bud off of trans Golgi (where sorting takes place) => right proteins sorted into
lysosomes, lysosome matures
• In ER, Lysosomal proteins tagged with phosphorylated mannose residues
- Lysosomal protein has sequence that allows it to be recognized by
phosphotransferase that transfers phosphate to mannose
- N-glycosylation in RER
- Tagged lysosomal enzymes recognized & captured by mannose 6 phosphate receptors
(MPRs) in Golgi
- Gathered in clathrin-coated vesicle, destined for lysosome
- Clathrin dissociates from vesicle; MPRs dissociate from lysosome (because of low pH)
& recycled
➢ If MPR doesn’t dissociate: either lysosomal enzyme goes back to Golgi & comes
back out, or receptors ends up in lysosome & degraded
• Why are lysosomal enzymes only active in lysosome but not before that?
- Lysosomal enzymes evolved to be functional at low pH (4-5), which occurs in
lysosome
- To make lysosome acidic: proton pumps pump H+ into lysosome using ATP (against
gradient)
Document Summary
In dead cells: immunostain for protein in lysosome; in live cells: tag with gfp. This image: (uses neither of those 2) using dye (lysotracker) selective for lysosomes; dye is everywhere else in the cell, but only fluorescing in lysosome. Dye takes advantage of lysosome property that makes it only fluoresce there: dynamic organelles responsible for receiving and degrading macromolecules from the secretory, endocytic, autophagic and phagocytic membrane trafficking pathways. Garbage disposal, specialized to destroy things that are toxic, can accumulate. Discovered enzyme glucose 6 phosphatase in a fraction of cell associated with membrane. Em looking at that fraction of cell -> they"re lysosomes. Structure: heterogeneous appearance including acid hydrolases, wide size range: 25nm 1um in diameter. After internalization: cargo sorted in endosomes, those destined for degradation sorted to lysosomes. Ldl taken up thru endocytosis -> secretary pathway into early endosome -> receptors recycled back to surface, ldl transferred to lysosome & degraded.
