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Block 1 Week 2 > Secretory Vesicles & Lysosomal Storage Disease > Flashcards

Secretory Vesicles & Lysosomal Storage Disease Flashcards

1
Q

PM in eukaryotic cell? How get proteins in to the cell/organelle?

A
  • PM is impermeable for large macromolecules, semi-permeable for smaller molecules
    -use active transport to bring proteins in the cell/organelle
    from the outside
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2
Q

what are the three major mechanisms for protein transport between compartments of the cell?

A

1) nuclear localization signals, chaperon proteins
2) specific transporters
3) lipid/protein packaging to carry cargo

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3
Q

why do cells require vesicular traffic? Types of vesicular traffic?

A
  • so can quickly respond to env. changes

- exocytosis and endocytic pathways

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4
Q

exocytotic pathway?

A
  • secretory pathway that delivers newly synthesized proteins, carbs, lipid to the PM or extracellular space
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5
Q

endocytotic pathway?

A

cells remove PM components & deliver to internal cell compartments called endosomes by endocytosis;
-contents can be recycled or sent to lysosomes to be degraded

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6
Q

what is vesicular transport?

A
  • involves transfer of luminal cargo & membranes
  • transport vesicles bud from the donor cell (or organelle)
  • vesicles fuse w/ acceptor cell(or organelle)
  • TIGHTLY controlled, never spontaneous
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7
Q

how do you make secretory proteins?

A
  • ## proteins meant for secretion or transmembrane work need a signal sequence/ signal peptide which targets the ER
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8
Q

Steps for synthesis of secretory proteins?

A

1) protein has signal sequence (6-12AA; CH0 side chain)
2) bound by SRP, stops trans. guides mRNA-ribosome complex to SRP receptor on ER
3) signal sequences transferred to translocon; moves protein into ER lumen
4) SRP removed from ribosome, trans continues
5) signal peptide cleaved by signal peptidase
6) PTM can then occur

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9
Q

what is a signal sequence?

A
  • 6-12 amino acid; CH0 side chain

- is on proteins meant to be secreted or be transmembrane proteins

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10
Q

what is SRP?

A
  • signal recognition particle
  • binds the signal recognition sequence on growing AA chain in trans
  • guides the secretory protein to ER to bind SRP-receptor & finish translation
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11
Q

What proteins enter the ER to finish translation?

A

1) proteins en route to other destinations

2) ER resident proteins

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12
Q

How identify proteins en route to other destinations?

A
  • destinations inside or outside the cell

- Golgi resident proteins, endosmomal & lysosomal proteins, cell surfface proteins, secreted proteins

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13
Q

What are ER resident proteins?How ID them?

A
  • chaperone proteins, protein disulfide isomerase

- these proteins carry an ER retention signal

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14
Q

What happens when proteins enter the ER (x3)?

A

1) post-translation modifications
2) quality control of proteins (calreticulin)
3) most are N-glycosylated

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15
Q

what is N glycosylation?

A
  • the covalent addition of sugars to proteins
  • most soluble/membrane associated proteins made in ER are glycoproteins
  • signals that the protein can be sent to Golgi for further packaging
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16
Q

Calreticulin and quality control of proteins that enter ER? Purpose?

A
  • along with calenxin are quality control proteins
  • detect misfolded proteins by binding to oligosaccharides incompletely folded proteins
    1) to retain proteins in the ER
    2) act as chaperones to prevent unfolded protein aggregation
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17
Q

Post-Translational modification in the ER?

A
  • formation of disulfide bonds in proteins (due to oxidizing env)
  • glycosylation of proteins, to help with folding tagging to go to the Golgi
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18
Q

The Golgi structure?

A

1) has cis, medial, and trans Golgi networks

2)

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19
Q

How proteins get from Er–> Golgi?

A

1) proteins taken from ER–> cis-Golgi via COPII vesicles

2)

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20
Q

the secretory pathway (specific x5

)?

A

1) proteins go ER–> cis-Golgi via COPII vesicles
2) vesicles fuse, form ER-Golgi intermediate compartment or ERGIC(temporary) or vesicular tubular cluster (VTC)
3) ERGIC is sorting station, returns proteins w/ ER retention sequences via COP1
4) proteins meant for Golgi go from VTC (ERGIC)–> Golgi via microtubules
5) proteins modified, exist trans Golgi for delivery to target site

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21
Q

secretory pathway general (x4)

A

1) ER
2) vesicular tubular cluster (VTC/ERGIC)
3) Golgi
4) Trans Golgi Network (TGN)

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22
Q

what is topology refer to in regards of secretory proteins?

A
  • refers to folding

- is determined by modifications of the proteins

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23
Q

what is topology refer to in regards of membrane proteins?

A
  • refers to folding
  • number of membrane domains
  • orientation w/ respect to cytoplasm
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24
Q

topology & orientation assumed in ER?

A

1) regions destined for exterior face of ER lumen
2) orientation maintained throughout secretory pathway
3) assembly of multi-meric complexes
4) folding of secretory proteins

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25
Q

types of protein processing during formation of secretory vesicles?

A

1) condensation/ concentration
2) lysosomal & secretory proteins sorted
3) apical vs basolateral sorting in epithelial cells
4) proteolytic processing

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26
Q

What is proteolytic processing?

A

-is that may hormones, neuropeptides & secreted enzymes are made first as inactive protein precursors (pre-pro-peptide)

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27
Q

what are the steps of proteolytic processing?

A

1) Pre-pro-peptide
2) pro-peptide
3) peptide

28
Q

proteolytic cleavages?

A
  • cleaving of pre & pro parts of the peptide

- begin in trans Golgi network, continue in secretory vesicles & ECF after secretion occurs

29
Q

What are the 3 protein sorting pathways in the trans Golgi? What makes up the secretory pathway?

A
  • constitutive secretion
  • regulated secretion
  • lysosome directed

secretory pathway= constitutive & regulated secretion

30
Q

constitutive vs regulated secretion?

A

1) constitutive: occurs continuously

2) regulated: in response to a trigger (ex. neurotransmitter release)

31
Q

What is bidirectional transport of proteins & cargo?

A
  • the idea that membrane enclosed membranes can more forward (toward Golgi & PM) or move backwards (toward to ER)
  • anteriograde & retrograde transport
32
Q

Anteriograde transport

A
  • moving membrane enclosed products forward toward the PM
    1) Er–> Golgi
    2) Golgi–> PM (exocytosis)
33
Q

retrograde transport? the two different types

A
  • moving membrane enclosed products back to ER (retrieval)
    1) from PM to lysosomes to (endocytosis or salvage pathways)
    2) from Golgi back to the ER (protein quality control)
34
Q

How do we distinguish between indirect/ineffecive vs direct/effective trafficking?

A

1) vesicle is dysfunctional & distracts overall well being of cell
2) vesicle performs effectively by taking most direct route
* based on coat proteins of cargo*

35
Q

What are coat proteins?

A
  • involved w/ function, processing & transport
  • different vesicle have diff coat proteins which effect their movements/ end locations
    ex: COPI; COPII; Clathrin
36
Q

What happens if a vesicle has the wrong coat protein?

A
  • wrong type of coat protein affects vesicle performance & cellular function
  • vesicles can go to the wrong location
37
Q

why is directing proteins to specific cell membrane regions important?

A
  • most cells in tissues are polarized, have 2 (or more) distinct PM domains diff vesicles can be directed to
  • depending on the specific nature of the PM, depends which kind of vesicle it requires
38
Q

epithelial cells & importance of accurately directing proteins?

A

-have two distinct membranes (basal lamina & apical surface)
-secrete distinct products at each membrane
=direct pathway of membrane protein sorting

39
Q

what prevents proteins & lipids from diffusing between the two domains?

A

-a ring of tight junctions (composed of proteins)

40
Q

how do newly synthesized proteins reach their proper plasma membrane?

A

1) direct pathway

2) indirect pathway

41
Q

direct membrane protein sorting?

A
  • used by gut epithelial cells
42
Q

indirect membrane protein sorting?

A
  • protein is retrieved from inappropriate PM domain by endocytosis, then transported to correct domain via early endosomes (transcytosis)
43
Q

What is transcytosis?

A
  • protein is retrieved from inappropriate PM domain by endocytosis, transported back to correct domain via early endosomes
  • used by liver hepatocytes to
44
Q

endocytosis overview?

A

1) outside material taken up in clathrin-coated vesicles (bud from PM & fuse w/ early endosomes)
2) early endosomes become late endosomes (decreased pH) = lysosome precursors
3) membrane components recycled to PM
4)

45
Q

what do recycling endosomes do?

A
  • recycle membrane components from the clathrin-coated vesicles back to the cell’s PM
46
Q

Endosome maturation most important step?

A
  • the lowering of internal pH of endosomes to 5.5

- allows lysosomal acid hydrolyses to come from trans Golgi

47
Q

phagocytosis

A
  • uptake of large particles by cell

- antigen is recognized on PM, ingested by phagocyte, forms PHAGOSOME

48
Q

pinocytosis

A
  • endocytosis of small particles
  • small particles brought into cell small pinocytotic vesicles
  • vesicles fuse w/ lysosomes to hydrolyze particles
  • used for nonspecific absorption of extracellular fluids
49
Q

autophagy

A

-degradation of cytoplasm proteins & organelles by enclosure in vesicles from the ER that fuse w/ lysosomes

50
Q

what do all secretory proteins pass through?

A

-pass through the ER to the Golgi to the PM

51
Q

what happens when misfolded secretory proteins are IDed in the Er?

A
  • should be identified in the ER
  • glycosylation used as tag for folding
  • incomplete multimers treated as misfolded
  • unfolded protein response turns up chaperone & degradative enzyme expression
52
Q

chaperone proteins?

A
  • bind misfolded proteins & try to refold them correctly
  • irreparably misfolded proteins are degraded by proteosomes
53
Q

What happens to misfolded proteins that can’t be refolded?

A

1) dislocation back to cytosol
2) deglycosylation by N-glycanase
3) ubiquitinylation
4) degradtion in proteosomes

54
Q

Degradation of misfolded proteins?

A
  • 1/3 of newly synthesized proteins are degraded

- initiated by ubiquitinylation process

55
Q

Where do misfolded proteins go to be degraded?

A
  • misfiled proteins exported from ER & degraded in cytosol
  • ubiquitinylation targets misfolded proteins to be degraded in proteosomes by proteolysis
56
Q

What are the properties of lysosomes?

A
  • membrane enclosed organelle w/ hydrolytic enzymes
  • pH 5.5; enzymes only work at this pH
  • need for cell health & fight off pathogens
57
Q

Primary purpose of lysosomes (x4)?

A
  • the digestion & removal of
    1) extra/unneeded organelles
    2) used up proteins&extracellular components; (recycle PM membrane components)
    3) autophagy digestions
    4) viruses & bacteria
58
Q

early endosomes (EE)?

A
  • first compartment in endocytic pathway
  • receives vesicles coming from cell surface
  • acid pH dissociate slogans from receptors
  • sorts vesicles into lysosomes or late endosomes
59
Q

late endosomes

A
  • receive material from EE &phagosomes (phagocytic pathway)
  • final sorting stage before lysosome fusion
  • pH=5.5
  • delivers acid hydrolyses to lysosomes from Trans Golgi
60
Q

from late endosomes to lysosomes ?

A

-formed by fusion of endosome transport vesicles

61
Q

vesicles?

A

thin membrane sac tha transports products for degradation, secretion, transport or specialized functions
-lysosomes & vacuoles =type of vesicles

62
Q

vacuoles

A
  • organelles w/ secretory, excretory or storage functions
  • more important in plants
  • larger than vesicles, contain mostly H20,
  • lysosomes bind & clear out vacuoles
63
Q

Autophagosomes

A
  • double membrane structure that engulfs organelles & proteins within the cytoplasm then fuse w/ lysosomes
  • key role in autophagy
64
Q

Autolysosome?

A
  • when autophagosome fuses w/ lysosome

- terminal step in generation of autophagic structure

65
Q

how separate lysosomal enzymes vs secreted protein products?

A
  • use M6P (Mann6 phosphate) coat on vesicles that need to fuse with late endosomes
  • M6P added in the Golgi
66
Q

lysosomes & the immune responses?

A
  • outside antigens (microbes) engulfed by endocytosis & fuse w/ lysosome in phagocytic cell
  • hydrolytic enzymes digest antigen into small peptides , presented on surface of MHC Class 2 T cells (inflammatory response)
  • some bacteria can evade this by enclosing itself in vacuole that doesn’t fuse w/ lysosome
67
Q

Hydrolytic enzymes?

A

-enzymes within the lysosomes that degrade bad stuff in the lysosome

Block 1 Week 2 (9 decks)

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