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30 Cards in this Set

  • Front
  • Back
what is the structure of the lysosome?
membrane bound organelle in the cytoplasm

lysosome mbns have proteins to transport nutrients out to the cyto and have a proton pump
how is autodigestion by a lysosome prevented?
lysosome mbn

inside lysosome is acidic pH, which is optimal for lysosomal enzymes

glycosylation of lys enzymes
what do lysosomes look like on EM?
electron dense, DARK
what's inside a lysosome?:
acid hydrolases and material being digested
what are the classes of lysosomes?
primary lysosome: contains enzymes but NO substrate yet

secondary lysosome: contains lysosomal enzymesand substrate w/ pH 5

tertiary lysosomes (aka residual bodies): old lysosomes w/ indigestible or undigested substrate
how do you ID a lysosome?
need enzyme histochemistry to ID for sure. can detect acid phosphatase.

1. add organic phosphates
2. add lead salts to preciptate cleaved PO4 as lead phosphate (visible by EM)
how do proteins move from the trans Golgi to lysosomes?
Dependent on addition of mannose 6-phosphate to hydrolase.

1. Enzymes destined for lysosomes are modified by adding phosphate to C6 of mannose in an oligosaccharide.

2. N-acetylglucosamine phosphotransferase adds phosphorylated N-acetylglucosamine to mannose

3. golgi mbn has M6-P receptors and clathrin coated vesicles pinch off -> fuse w/ lysosomes where enz activated by low pH
what is heterophagy?
digestion of materials taken up from outside the cell by endocytosis
what is autophagy?
digestion of parts of the cell's cytoplasm
what is crinophagy?
digestion of stored secretory material produced by the same cell
How does receptor-mediated endocytosis work?
1. ligand binds to specific receptor, a transmbn protein

2. receptors cluster, form clathrin-coated pit, then pinches off to form a vesicle

3. the vesicle fuses with an early endosome, where the ligands and receptors dissociated

4. multivesicular bodies are intermediates b/w early and late endosomes

5. late endosomes, which either mature into secondary lys or transfer contents
How does pinocytosis usually occur?
Usually pinocytotic vesicles are uptaken WITHOUT a coat (nonspecific).

Receptor-mediated endocytosis occurs in some cells.
What types of heterophagy are there?
how does autophagy occur?
lysosomes surround region of cytoplasm and form 2 mbs

the inner mbn breaks down and the enzymes eat stuff up
when does crinophagy occur?
when there's a long time before the secretory product is needed again
when does exocytosis of lysosomes occur?
when cell is stressed and in specialized cells (e.g. release of hydrolytic enz by osteoclasts during bone resorption)
what is exocytosis of lysosomes?
lysosome secretion or "cellular defecation"

elimnate indigestible debris
What are Tay Sachs, metachromatic leukodystrophy, and Hurler's disease examples of?
Lysosomal storage diseases where there are defects in genes encoding hydrolytic enzymes
What is I-cell disease an example of?
Lysosomal storage disease where there's a mutation affecting sorting and segregation of lys enzymes.

End up with Inclusions
What do proteasomes do?
They degrade damaged and misfolded proteins in the cytoplasm.
How do proteins get targeted to the proteasome?
They use ubiquinylation to target the gene for digestion by the proteasome
What are peroxisomes?
cytoplasmic organelle w/ a SINGLE mbn

found in liver and kidney

spherical to ovoid, usu 1-5 times width of mit
what do peroxisomes do?
contain oxidases and form H2O2, which detoxifies toxins or kills microorganisms.

very long fatty acids get oxidized, to produce acetylCoA (transported to other cells)and H2O2.

important in ethanol metabolism.

catalyze 1st step in formation of plasmalogen (most abundant phospholipid in myelin)
What breaks down the toxic H2O2 in peroxisomes?
enzyme catalase breaks down hydrogen peroxide to water and oxygen
How are peroxisomal enzymes targeted?
Enz synthesized on free polysomes -> transferred to peroxisomes

Entry into peroxisomes requires a secific AA sequence (i.e. ser-lys-leu)

1. enzymes bind to cytosolic receptors
2. bind to docking proteins on surface of peroxisomes, which then allow entry
What are Zellweger Syndrome and neonatal adrenoleukodystrophy examples of?
Class 1 peroxisomal enz disorder

Mistargeting to cytosol

Lacks essential pathway involving both N-terminal and C-terminal targeting seq., leading to "empty" peroxisomes and enz end up in cytosol
What is rhizomelic chondroplasia an example of?
Class 2 peroxisomal enz disorder

Mistargeting to cytosol

Lacks only N-terminal targeting sequence
What is X-linked adrenoleukodystrophy (ADL) an example of?
Class 3 peroxisomal enz disorder

Only single peroxisomal proteins are affected. Enzyme activity/subcellular location is compromised.
What are the types of disorders disrupting peroxisomal enzymes?
Class 1: mistargeting to cytosol w/ defects in N and C terminals

Class 2: mistargeting to cytsosol w/ defect in only N-terminal

Class 3: Single proteins affected
what are peroxisomal proliferators?
specific drugs, chemicals, or high fat diets cause an increase in # of peroxisomes and oxidative capacities

do not increase catalase content

ex: fatty acids, aspirin, insecticides, wood preservatives

may cause cancer...oxidative damage!