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BSCI330 SPRING > exam 3 vesicular transport > Flashcards

exam 3 vesicular transport Flashcards

1
Q

what occurs via vesicular transport

A

movement of proteins between the ER, most membranous organelles, and the cell surface

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2
Q

what do proteins have to undergo before using vesicular transport to get into ER

A

undergo transmembrane transport

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3
Q

what are proteins transported by in vesicular transport

A

transported by vesicles, which bud off of one organelle and fuse with another and deliver contents that way

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4
Q

what are proteins guided by

A

specific coat and targeting proteins

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5
Q

what do retrograde pathways do

A

they are reverse pathways that allow the return of “escaped” proteins to original organelles and the recycling of targeting proteins

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6
Q

what serves as roadways for vesicular transport

A

cytoskeleton

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7
Q

why do proteins never have to cross a membrane from one side to the other using vesicular transport

A

vesicular transport keeps topological similarities

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8
Q

what does vesicular sorting depend on

A

the assembly of a special protein coat formed at specific locations along a given donor compartment

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9
Q

what do coat proteins do

A

deform membrane to start vesicular formation and initiate targeting to next compartment

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10
Q

what are the 3 main classes of coat proteins

A

COPI, COPII, clathrin

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11
Q

what is COPII used in

A

coating vesicles that bud off of ER and go to golgi

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12
Q

what is COPI used for

A

vesicles that bud off of golgi and move internally or go to ER and plasma membrane

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13
Q

what is clathrin used for

A

transport between cell surface, golgi, and endosomes

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14
Q

what represents the initial step in vesicle formation

A

coat proteins

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15
Q

what do transport vesicles bud off as

A

as coated vesicles that have a distinctive cage of proteins covering their cytosolic surface

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16
Q

what closes off membrane into spherical vesicle

A

a forced curvature of membrane due to coat proteins - before the vesicle fuses with a target membrane, the coat is discarded to allow the two cytosolic membrane surfaces to interact directly and fuse

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17
Q

what marks organelles and membrane domains

A

phospholipids containing inositol head groups

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18
Q

how do coat proteins know where they are

A

lipid concentrations are different in different domains

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19
Q

what/where can inositol get phosphorylated by

A

inositol can get phosphorylated at various locations by different lipid kinases

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20
Q

what can different phosphorylations be recognized by

A

other proteins, which can then tag membranes to identify them - kinases are selectively associated with different membranes

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21
Q

what can phosphoinositides recruit

A

various proteins that possess lipid binding domains (which only recognize a specific type of PI)

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22
Q

how can binding be regulated

A

by phosphorylating or dephosphorylating polar head groups

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23
Q

what do adapter proteins bind to

A

membrane proteins or membrane to recruit coat proteins (often bind to cargo receptors)

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24
Q

what controls coat assembly

A

coat recruitment GTPases

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25
Q

what does assembly of coat proteins involve

A

binding of GTP form

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26
Q

what does disassembly of coat proteins involve

A

GTP is hydrolyzed to GDP

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27
Q

which of cytosol and ER membrane bound forms of coat proteins are inactive and active

A

GDP is in cytosol = inactive

GTP is ER membrane-bound = active

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28
Q

what allows for specificity in vesicle targeting

A

surface markers that identify vesicles according to their origin and type of cargo

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29
Q

what is recognition of donor vesicles by acceptor membranes controlled by

A

SNAREs and Rabs

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30
Q

what do Rabs do

A

type of GTPase that works together with other proteins to regulate the initial docking and tethering of the vesicle to the target membrane

31
Q

how do Rabs transfer to SNAREs

A

Rabs release protein when it is hydrolyzed to GDP - this transfers to SNAREs

32
Q

what do SNAREs do

A

provide specificity and catalyze vesicular fusion of the target membrane

33
Q

what are v-SNAREs and t-SNAREs

A

v = vesicle
t = target membrane
make a very tight interaction and the force of this drives fusion events between membranes - separated later using ATP hydrolysis

34
Q

how do Rab and SNAREs work together

A

Rab tethering protein catches vesicle, SNAREs force fusion between two membranes

35
Q

how does cargo recruitment work

A
  • membrane proteins have exit signals in the cytosolic tails that are recognized by coat proteins
  • soluble proteins bind to cargo receptors that have exit signals in their cytosolic tails
36
Q

what happens after transport vesicles bud off of ER

A

they fuse together to form intermediate compartments called vesicular tubular clusters

37
Q

what do vesicular tubular clusters do

A
  • travel towards the cis golgi via motor proteins on microtubule tracks
  • generate coated vesicles going back to the ER (COPI coat) - retrograde transport
38
Q

what happens with ER retrieval signals

A
  • membrane ER resident proteins retrieve signals in their cytosolic tails, recognized by COPI coat proteins
  • soluble ER resident proteins retrieve signals within their structure and bind to receptors
39
Q

what are the two models for how cargo travels through the golgi

A

static model and dynamic model

40
Q

what is the static model

A

golgi stacks (cisterae) remain the same throughout - vesicles travel between them, moving proteins

41
Q

what is the dynamic model

A

golgi stacks (cisternae) move upward, changing their protperties slightly as they migrate

42
Q

how do enzymes get returned

A

through vesicular transport in retrograde directions

43
Q

how do proteins leaving golgi get to plasma membrane

A

vesicles carrying them fuse with the plasma membrane via exocytosis

44
Q

what are the two basic pathways of secretion

A

constitutive secretory pathways and regulated secretory pathway

45
Q

what happens with constitutive secretory pathway

A
  • once you leave golgi, directed to plasma membrane which you fuse with
  • no additional signal required
46
Q

what happens with the regulated secretory pathway

A

secreted components are concentrated into secretory vesicle which moves to plasma membrane. it requires an external signal to trigger fusion of vesicle with plasma membrane

47
Q

what are clathrin-coated vesicles used for

A

transport between plasma membrane, endosomal system, and golgi

48
Q

what is the structure of clathrin

A

composed of three copies each of heavy and light chains; arranged in a triskelion

49
Q

what does clathrin interact with

A

cargo receptors and other markers to drive vesicle formation, then clathrin coat is lost

50
Q

what is dynamin

A

a GTPase that is a cytoplsasmic proteins which control the pinching-off of clathrin-coated vesiclse

51
Q

how does dynamin work

A
  • wraps around the stem of the budding vesicle
  • brings inner leaflet membranes of vesicles together
  • fusion of these membranes severs the vesicle from the donor compartment
  • GTP hydrolysis regulates rate of vesicle pinching off
52
Q

what are the characteristics of lysosomal enzyme cargo

A

soluble, carry a unique marker - mannose 6-phosphate (M6P) groups

53
Q

what happens when lysosomal enzyme cargo is recognized by M6P receptor in golgi network

A

it’s packaged into clathrin-coated vesicles for delivery to lysosomes

54
Q

what are endosomes

A

intermediate organelles in vesicular transport pathways between plasma membrane, lysosomes, and golgi

55
Q

what are the three classes of endosomes

A

early, late recycling

56
Q

what are early endosomes

A

develop from endocytosis

57
Q

what are late endosomes

A

mature from early endosomes to become more like lysosome compartments

58
Q

what are recycling endosomes

A

compartment that after some cargo has delivered to endosomes, compartments can go back to plasma membrane

59
Q

what do endosomes eventually mature into

A

lysosomes by becoming increasingly acidic because of addition of proton pumps

60
Q

what do proton pumps do

A

move protons from cytosol and concentrate them inside compartment to become more acidic

61
Q

what happens in exocytosis

A

vesicle fuses with plasma membrane and releases cargo

62
Q

what happens in endocytosis

A

vesicle comes in from outside and pinches off

63
Q

what does low pH activate enzymes to do

A

to be able to degrade biological molecules

64
Q

what are multivesicular bodies

A

vesicles with vesicles in them - characterizes maturation of late endosomes

65
Q

what happens to membrane proteins and lipids as vesicle cargo

A

they’re removed from the plasma membrane and some will be recycled back to surface, some will be degraded

66
Q

what happens to soluble proteins as vesicle cargo

A

they’re from extracellular space and are carried into the lumen to be degraded

67
Q

what are the common components targeted during exocytosis

A

cell surface receptors and the ligands that bind them

68
Q

what is phagocytosis

A

cellular eating - the ingestion of large particles, such as microorganisms or dead cells via vesicles called phagosomes

69
Q

what is pinocytosis

A

cellular drinking - the ingestion of fluids and solutes by vesicles called pinocytic vesicles, including receptor-mediated endocytosis

70
Q

what do cells do constantly in terms of endocytosis

A

pinocytosis - doesn’t require a trigger - it’s how cells get fluids in cell and sample nutrients

71
Q

how does cholesterol get into cells

A

via receptor-mediated endocytosis

72
Q

what receptors generally get recycled to the cell surface

A

receptors that involve the transport of nutrients

73
Q

what receptors generally get degraded

A

receptors involved in signaling events because that turns off signaling to reset the cell

74
Q

what is transcytosis

A

moving from one side of a polarized epithelium to another

BSCI330 SPRING (24 decks)

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