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Histology/Cell Biology > Lysosomes, Protein Turnover, & Peroxisomes > Flashcards

Lysosomes, Protein Turnover, & Peroxisomes Flashcards

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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
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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)
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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
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4
Q

adaptins

A
  • bind to receptor internalization sequences and clathrin on cytosolic side (receptor-mediated endocytosis)
  • possess specificity for families of receptors
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5
Q

stain for acid phosphatase

A
  • EM

- lysosomes appear more dense, distinguishable from other organelles

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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
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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
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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
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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

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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
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11
Q

fluid phase endocytosis

A
  • membrane invaginate and takes up whatever is contained in vesicle it forms
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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
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13
Q

autophagy

A
  • degradation of cellular components
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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
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15
Q

dynamin

A
  • works with clathrin and adaptin to create endosome during receptor-mediated endocytosis
  • constricts PM to help form vesicle
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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
Q

I-cell disease

A
  • 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
Q

ubiquitin proteasome pathway

A
  • major pathway responsible for protein turnover
  • polyubiquitin tag allows for recognition by proteasome complex
  • proteins broken down to peptides
27
Q

proteasome complex

A
  • 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
Q

functions of ubiquitin/proeasomes (regulation by degradation)

A
  • degrade abnormal proteins
  • regulation of cell division (cyclins degraded)
  • regulates transcription factors
  • regulates bulk proteins in skeletal muscle wasting
  • quality control of ER
29
Q

How do proteasomes function in quality control of ER?

A
  • 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
Q

peroxisomes

A
  • degrades H202 to H2O
  • has occlusions (urioxidate crystals)
  • functions in processes that create peroxide
31
Q

peroxisomes function in which processes?

A
  • fatty acid oxidation
  • lipid synthesis
  • cholesterol synthesis
  • myelin synthesis
  • alcohol breakdown
32
Q

How is biogenesis of peroxisomes distinct from lysosomes?

A
  • 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
Q

Zellweger’s syndrome

A
  • mutations in peroxisome receptor that recognizes tripeptide sequence
  • constituent proteins unable to be taken up by peroxisomes (can’t break down peroxide)
34
Q

Adrenoleukodystrophy

A
  • defect in myelin synthesis

- can lead to neuronal/muscular weakness

Histology/Cell Biology (12 decks)

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