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Cell Biology > The Secretory Pathway > Flashcards

The Secretory Pathway Flashcards

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1
Q

what is constitutive exocytosis?

A

continuous secretion

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2
Q

give an example of regulated secretion?

A

e.g. just had a meal and get an elevation of blood glucose and gets insulin secretion

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3
Q

what happens in the ER?

A
  • post translational modiciations
  • specific proteolytic cleavage
  • glycosylation
  • disulphide bond formation
  • folding and assembly of multiple subunit proteins
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4
Q

what is glycosylation?

A

covalent addition and processing of oligosaccharides (carbohydrates)

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5
Q

what is involved in the folding and assembly of multiple subunit proteins?

A
  • requires chaperones
  • disulphide bond in a protein will be extracellular or secreted protein
  • happens in the lumen of the ER
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6
Q

what is correct folding?

A
  • entry is in unfolded form when it enters the ER
  • in the ER proteins generally reach their corect confirmation in minutes
  • mediated by chaperones
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7
Q

what are chaperones?

A
  • undergo cycles of binding and release of polypeptide substrate
  • domains move powered by ATP hydrolysis
  • binding and release helps substrate polypeptide adopt correct confirmation
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8
Q

what is disulphide bond formation?

A
  • part of the correct folding process
  • the lumen is oxidising whereas the cytoplasm is reducing
  • get sulphur cross-linked (uses protein duslphide isomerase (PDI))
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9
Q

what does prolyl isomerase do?

A

proline isomerisation

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10
Q

what configuration do most peptide bonds need to be in?

A

trans configuration - more favourable

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11
Q

what configuration is proline?

A

can be in the cis or in the trans state

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12
Q

what is proline isomerisation?

A

interconversion can be accelerated by peptidyl propyl isomerase (PPI) enzymes

  • helps transformation from trans to cis
  • can shif conformation
  • involved in protein folding and regulation
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13
Q

what is N linked glycosylation?

A
  • Asparagine = Asn = N

- N glycosylation is occurring on asparagine residues

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14
Q

what is glycosylation?

A
  • have a protein in with a lipid chain
  • on the cytolasmic side it pick up 2-N-acetyl-glucosamine residues and 9 mannose residues
  • it then flips across the membrane
  • in the ER lumen gets 3 glucose added
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15
Q

how are glucose residues are involved in quality control?

A
  • help determine if a protein is folded correctly
  • unfolded proteins retain a glucose that binds to ER chaperones, calnuxin and calreticulin, retaining them in the ER
  • glucose group is added by glucosyl transferase
  • folded proteins have glucose removed and allowed exit from the ER
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16
Q

how do prtoeins exit the ER?

A

use Sec61

17
Q

what happens if folding fails?

A

proteins are retro-translocated into the cytosol and degraded by the proteasome

18
Q

when is UPR triggered?

A

triggered by ER chaperones when unfolded proteins accumulate in the ER

19
Q

what is the cause UPR?

A

the expression of a mutant protein causing disease

20
Q

how does UPR work?

A
  • triggers the upregulation of chaperone expression
  • increased from the ER and proliferation of the ER
  • prolonged UPR leads to cell death
21
Q

how do the proteins leave the ER?

A

leave the ER in COPII coated transport vesicles

22
Q

what do the soluble cargo proteins do?

A
  • has an exit signal
  • acitvely packaged into COPII
  • pinch off ER to form a vesicle
23
Q

what is the role of the exit signal?

A
  • it binds a receptor
  • receptor than binds to cytosolic proteins
  • concentrates receptor into budding vesicle
24
Q

what is the assembly of the coat initiated by?

A
  • Sec12 binding to Sar1

- Sar1 exchanges GDP for GTP

25
Q

what is the process of coat assembly?

A
  • Sec12 binding to Sar1
  • Sar1 exchanges GDP for GTP
  • GTP bound Sar1 binds to the ER and acts as a nucleus for Sec23/24 binding
  • Sec24 binds transmembrane cargo
  • coat assembly is completed by the binding of Sec13/31 to the Sar-GTP, Sec23/24 complex
26
Q

what does the COPII coat allow?

A

allows membrane curvature and budding

27
Q

what can get caught up in vesicle budding?

A

resident ER proteins

28
Q

what do vesicles move along?

A

microtubules

29
Q

how do vesicles move from the ER to the Golgi?

A
  • move from the ER to the cis Golgi
  • have Golgi intermediate compartments
  • COPII coat going in
  • COPI coat retrieves material back to the ER (retrograde traffic)
30
Q

why is it important that material is retrieved back to the ER?

A
  • dont want to lose the ER enzymes if they move forward to the Golgi
31
Q

what is ER retrieval and retrograde transport?

A
  • ER proteins retried
  • contain a KDEl sequence
  • KDEL receptors bind cargo with KDEl sequences
  • KDEL receptors have a ER retrieval signal which allows them to be packaged into COPI coats
32
Q

how do you get from the cis Golgi to the trans Golgi?

A
  • get a lot of vesicle budding from one cisternae to the next
  • fusion requires SNAREs regulated by Rabs
  • each modification is specific to each cisternae (can be additions and removals)
33
Q

what happens at the trans Golgi?

A
  • get stored
  • constitutive secretion
  • regulated secretion
34
Q

what are the function roles of glycan?

A
  • folding in the ER
  • stability/protease resistance of proteins
  • golgi wont do exactly the same reactions to every protein
  • molecular interactions/recognition
  • blood groups are based off carbohydrates
  • immune response
  • signalling
  • architecture of the extracellular matric and cell to matrix attachment
  • glycan structures are altered in diseases
35
Q

what happens constituvely in the Golgi?

A
  • bulk flow
  • vesicles transported to the plasma membrane
  • get secreted
36
Q

what are the key points of targeting towards the lysosome?

A
  1. phosphoryaltion of mannose
    - 2. specific M6P receptor cycling between late endosomes and the TGN
  2. Acidic pH of late endosome releases M6P from the receptor
37
Q

what can defects in the delivery of lysosomes enzzymes cause?

A
  • defects in lysosomal degradation
  • substrates that are normally degraded start to accumulate
  • have mostly neurological symptoms

Cell Biology (10 decks)

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