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MCB 2050 > Endomembrane System Part 2 - Secretory Pathways > Flashcards

Endomembrane System Part 2 - Secretory Pathways Flashcards

1
Q

2 secretory pathways responsible for transporting cargo from TGN to pm/extracellular space

A

constitutive secretion pathway
regulated secretion pathway

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2
Q

gist of constitutive secretion pathway

A

materials are continuously transported via secretory vesicles from TGN to pm

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3
Q

what occurs in constitutive secretion pathway when secretory vesicles reach pm

A

they fuse via Rabs and SNAREs and release lumenal soluble cargo outside cell

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4
Q

what happens to vesicle membrane cargo components in constitutive secretion pathway

A

incorporated into plasma membrane

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5
Q

what is considered the default secretion pathway

A

constitutive secretion

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6
Q

what is the constitutive secretion pathway the pathway for

A

proteins not selectively sorted through biosynthetic pathway or regulated secretion

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7
Q

what do materials at TGN get packaged into in regulated secretion pathway

A

secretory granules

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8
Q

in regulated secretion, what occurs in response to cellular signal

A

granules stored in cytoplasm target to and fuse with pm and release their lumenal cargo outside cell

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9
Q

what pathway operates in the opposite direction of secretory pathways

A

endocytic pathway

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10
Q

gist of endocytic pathway

A

materials move into cell via gesticulation of pm and are either recycled back to pm or sorted to different intercellular destination

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11
Q

what are the 2 main processes for internalization

A

phagocytosis
endocytosis

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12
Q

gist of phagocytosis

A

uptake of large, particulate materials from extracellular space by specialized cells

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13
Q

what do FC receptors signal

A

reassembly of actin microfilament network

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14
Q

what are pseudopods

A

alterations in cytoskeleton that result in changes in shape of leukocyte-cell extentions

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15
Q

what does phagosome-lysosome fusion get blocked by

A

Mycobacterium tuberculosis

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16
Q

what are the 2 main endocytic pathway processes for internalization

A

bulk-phase endocytosis
receptor-mediated endocytosis

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17
Q

what is another term for bulk-phase endocytosis

A

pinocytosis

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18
Q

gist of bulk-phase endocytosis

A

non-specific uptake of extracellular fluids and plasma membrane proteins and lipids into small vesicles

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19
Q

with bulk-phase endocytosis, how often does the pm recycle

A

20-90min

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20
Q

gist of receptor mediated endocytosis

A

specific cell-surface (pm) receptor binds extracellular ligands and receptor-ligand complexes subsequently concentrated and internalized in clathrin coated transport vesicles

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21
Q

examples of materials internalized by receptor mediated endocytosis

A

M6P receptor bound lysosomal proteins escaped from TGN
receptor complexes with cell signalling hormones or growth factors
ferrotransferrin
cholesterol containing LDL

22
Q

what is AP2 adaptor coat protein

A

cytoplasmic protein serves as linker during clathrin-coast vesicle assembly at pm

23
Q

what are clathrin coated pits

A

specialized regions of PM where receptor-ligand complexes are concentrated and endocytic vesicles eventually form

24
Q

what is the inner (cytoplasmic) leaflet of the plasma membrane at coated pit enriched in

A

unique membrane phospholipids

25
Q

what is the membrane lipid microdomain enriched in

A

phosphoatidylinositol (PI) (4,5) P2

26
Q

what does the PI (4,5) P2 membrane lipid microdomain serve as

A

signal for recruiting AP2 with bound receptor-ligand into coated pit

27
Q

what does AP2 have multiple of

A

binding domains

28
Q

what are the 3 binding domains in AP2

A
  1. PI (4,5)P2
  2. cytoplasmic domains of pm transmembrane receptors
  3. clathrin
29
Q

what does AP2 form at cytoplasmic face of coated pit

A

inner layer of coat

30
Q

what is referred to as early endosome

A

nascent, uncoated endocytic vesicle

31
Q

what does degradation of endocytose membrane proteins involve

A

inward budding of vesicles into late endosome interior

32
Q

what does the inward budding of vesicles form

A

multivesicular late endosome or multivesicular body (MVB)

33
Q

what about MVB is unique

A

its morphology

34
Q

what does MVB contain numerous of

A

intralumenal vesicles

35
Q

comparison of MVB to transport vesicles

A

similar in size but opposite topology

36
Q

MVB topology

A

MVB vesicles bud away from the cytoplasm

37
Q

what do MVB vesicles selectively contain

A

membrane proteins destined for degradation in lysosome interior

38
Q

what mediates membrane cargo protein selection and inward vesicle budding

A

ESCRT machinery

39
Q

ESCRT: multi protein complex

A

soluble cytosolic protein constituents recruited to MVB surface

40
Q

what does multi-protein complex mediate

A

membrane cargo protein selection and inward vesicle budding

41
Q

ESCRT: what are endocytose membrane proteins destined for

A

degradation linked to mono-ubiquitin

42
Q

step 1 of ESCRT

A

signal for recognition by ESCRT protein Hrs and subsequent entry into newly-forming MVB

43
Q

what does Hrs recruit

A

addition ESCRT proteins

44
Q

what is step 2 of ESCRT

A

assemble to mediated inward budding and scission of nascent vesicle into MVB lumen

45
Q

what does Vps4 ATPase do

A

disassembles ESCRT complex

46
Q

step 3 of ESCRT

A

ESCRT components released into cytoplasm and recycled for additional rounds of MVB formation

47
Q

when ESCRT is hijacked by retroviruses what is similar

A

topology of vesicle budding at MVB is similar to enveloped retrovirus particle budding at plasma membrane in virus-infected cells

48
Q

What does HIV Gag protein function similarly to

A

ESCRT Hrs

49
Q

what is HIV Gag protein

A

major structural viral particle protein at pm and binds to and recruits (hijacks) ESCRT machinery to pm

50
Q

what does ESCRT mediate with retrovirus

A

budding and scission of nascent virus particle into extracellular space for subsequent infection of other cells

MCB 2050 (11 decks)

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