Lysosomes, Protein Turnover, & Peroxisomes Flashcards
1
Q
What is protein turnover?
A
- dynamic state of proteins (not static)
- single proteins don’t exist throughout entire lifetime of organism
- intracellular process dissociated from cell division
- rate is dif for dif proteins
2
Q
lysosomes
A
- family of vesicular structures (unimembrane)
- contain acid hydrolases –> enzymes that act optimally at acidic pH (5.0)
- acidity maintained by H+ pump using ATP (hydrolysis) –> stains basophilic
- contain integral membrane proteins called lysosomal associated membrane proteins (LAMP)
3
Q
clathrin
A
- forms coated pit during endocytosis (endosome formation)
- also coats transport vesicle produced by TGN that eventually fuses with late endosome to form lysosome
- clusters form structure of hexagons & pentagons
4
Q
adaptins
A
- bind to receptor internalization sequences and clathrin on cytosolic side (receptor-mediated endocytosis)
- possess specificity for families of receptors
5
Q
stain for acid phosphatase
A
- EM
- lysosomes appear more dense, distinguishable from other organelles
6
Q
fractionation & lysosomes
A
- easier to do on soft tissues (i.e. liver)
- iron injected into animal and taken into lysosomes –> separate out from rest of cytosol
- methodology can be used to assay various hydrolases contained within lysosomes
7
Q
mech of making transport vesicle containing hydrolases
A
- hydrolases glycosylated –> addition of Mannose-6-phosphate in cis stack of ER
- cluster in region of TGN (trans-Golgi network), facilitated by M6P receptors and sensory proteins
- form transport vesicles with assistance from clathrin
- pinches off, forming coated vesicle
8
Q
mech of transport vesicle –> lysosome
A
- coated vesicle (transport vesicle) containing M6P tagged hydrolases
- clathrin comes off and goes back to TGN
- vesicle membrane has info that allows it to fuse with endoscope to form endolysosome
- cleavage of phosphate from M6P, no longer bound to receptor (irreversible)
- M6P receptors recycled back into TGN
- incorporation of LAMP proteins, delivered by other vesicles
- as more H+ pumps get incorporated, endolysosome matures to lysosome
9
Q
role of phsophotransferase & phosphoglycosidase in lysosome formation
A
- turn a-D-mannose into mannose-6-phosphate
- end up with M6P tagged hydrolases that are specific to lysosome
10
Q
phagocytosis
A
- degradation of large structures that are brought into cells
- use specialized cells (macrophages)
- circulating factors in ECM binds to material
- recognized by cell and brought in using phagosomes (vesicle)
- fuse with endolysosomes or mature lysosomes –> breakdown
11
Q
fluid phase endocytosis
A
- membrane invaginate and takes up whatever is contained in vesicle it forms
12
Q
receptor-mediated endocytosis
A
- specific components recognized by receptors
- i.e. growth factors, insulin, etc.
- ligand binds to specific receptor
- clathrin coat (mediated by adaptins) on cytosolic side
13
Q
autophagy
A
- degradation of cellular components
14
Q
Compartment for Uncoupling of Receptors from Ligands (CURL)
A
- endososome (formed from receptor-mediated endocytosis) takes on tubular formation
- usually separates ligands from receptors
- receptors cluster and get recycled back to PM
15
Q
dynamin
A
- works with clathrin and adaptin to create endosome during receptor-mediated endocytosis
- constricts PM to help form vesicle
16
Q
normal process of LDL degradation
A
- binds to LDL receptors on cell surface –> located on binding domains
- forms vesicle that becomes endosome
- transport vesicles containing LDL receptors bud off and return to PM
- LDL degraded in mature lysosome
- free cholesterol released into cytosol –> tells HMG co-reductase not to produce more cholesterol
17
Q
hypercholesterolemia
A
- mutation in tail of LDL receptors
- receptors don’t bind to adaptin-clathrin complexes (receptor-mediated endocytosis not supported)
- can’t bring LDL in cell to be degraded –> no free cholesterol in cytosol
- HMG co-reductase (ER enzyme) normally turned off by free cholesterol in cytosol
- without –> not turning off de novo synthesis of cholesterol
- increased LDL
18
Q
microautophagy
A
- lysosome invaginates its own membrane
- internalizes material in cytoplasm or within its own membrane
19
Q
macrophagy
A
- cisternae of membrane (SER) gets activated to form auto-magic vacuoles
- enclose around region of cytosol and degrades material
20
Q
direct protein transfer
A
- directly, selectively takes in specific proteins through dif channels
- catalyzes their degradation
21
Q
degradation of membrane receptors (ex of microphagy)
A
- growth factor receptors –> degradation down regulates growth factors
- have certain info in tails that allows them to be tagged by ubiquitin (monoubiquitination)
- ligand binds with receptor and receptor tagged –> signals to cell not to recycle receptor
- invagination within lysosome –> receptors inside vesicle within lysosome (multivesicular body)
- provides mech for degradation of entire receptor (otherwise hydrolases wouldn’t be able to degrade receptor tails)
22
Q
ex of macrophagy
A
- SER surrounds part of cytosol with double membrane
- eventually material is degraded and end up with residual material
- induced in nutritional starvation (insulin and glucose, etc.)
- immediately produces energy for cell (non-specific) –> survival mech
23
Q
chaperone-mediated autophagy
A
- more selective pathway of autophagy
- pentipeptide sequence recognized by chaperones and complexes with them
- proteins and complex (hsc70) bind to specific channel on lysosome (lamp 2a)
- induction of lamp 2a proteins during starvation
24
Q
Tay-Sachs
A
- hydrolase gene not expressed –> causes accumulation of gangliosides
- accumulation of undigestible material (lipid whirls)
- cell fills up and eventually dies
- genetic
25
I-cell disease
- defect in attachment of M6P tag
- creation of inclusion bodies
- hydrolases are made by cell but not targeted to lysosome
- secreted out of cell and into blood
26
ubiquitin proteasome pathway
- major pathway responsible for protein turnover
- polyubiquitin tag allows for recognition by proteasome complex
- proteins broken down to peptides
27
proteasome complex
- proteins with specific sequences in primary/secondary/tertiary sequences allow them to be recognized
- protein is unwound and cleaved by different active sites within protease (barrel-shaped)
28
functions of ubiquitin/proeasomes (regulation by degradation)
- degrade abnormal proteins
- regulation of cell division (cyclins degraded)
- regulates transcription factors
- regulates bulk proteins in skeletal muscle wasting
- quality control of ER
29
How do proteasomes function in quality control of ER?
- co-translational (translocation arrest) = can recognize incorrect polypeptide sequence on cytosolic side
- post-translational (retrograde translocation) = recognizes incorrect polypeptide as its being transported out of ER
30
peroxisomes
- degrades H202 to H2O
- has occlusions (urioxidate crystals)
- functions in processes that create peroxide
31
peroxisomes function in which processes?
- fatty acid oxidation
- lipid synthesis
- cholesterol synthesis
- myelin synthesis
- alcohol breakdown
32
How is biogenesis of peroxisomes distinct from lysosomes?
- not made by classic ER-Golgi pathway
- membrane from SER
- proteins found in peroxisome made in cytosol and imported using specific signals (tri-peptide: Ser-Lys-Leu) recognized by receptors on peroxisomal membrane
- can also proliferate by fission
33
Zellweger's syndrome
- mutations in peroxisome receptor that recognizes tripeptide sequence
- constituent proteins unable to be taken up by peroxisomes (can't break down peroxide)
34
Adrenoleukodystrophy
- defect in myelin synthesis
| - can lead to neuronal/muscular weakness
