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BIO230 > Spatial organization > Flashcards

Spatial organization Flashcards

1
Q

importance of membrane trafficking

A
  • communicate with other cells
  • acquire resources

these require control and dynamic changes to the plasma membrane

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2
Q

roles of the

a. endoplasmic reticulum
b. plasma membrane
c. lysosome

A

a. makes proteins
b. acts as a barrier
c. breaks down proteins

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3
Q

basic principles of the biosynthetic-secretory and endocytic pathways

A
  1. polarized trafficking routes all throughout the system
  2. sorting stations
  3. retrieval mechanisms and general balance among routes
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4
Q

constitutive secretory pathway

A

functions in all eukaryotic cells (see lec 1 for diagram)

trans golgi network –> newly synthesized proteins and membrane lipids –> unregulated membrane fusion –> extracellular space

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5
Q

regulated secretory pathway

A

signal-induced pathway for specialized eukaryotic cells

trans golgi network –> secretory vessel sorting secretory proteins –> signal (i.e. hormone/neurotransmitter) –> intracellular signaling pathway –> regulated membrane fusion

  • vesicles stored until a signal triggers their docking and fusion
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6
Q

mature secretory vesicle

A

secretory vessel made from retrieving golgi components and concentrating cargo

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7
Q

extra plasma membrane

A

regulated secretion gives extra plasma membrane when needed

  1. cleavage furrow- one cell dividing into two
  2. phagocytosis- cell membrane forms a vesicle around organism (tends to be endosomes)
  3. wound repair (tends to be lysosomal fusing)
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8
Q

basic steps of endocytosis

A
  1. invagination- forming a cavity or pouch as the membrane indents into the cytosol
  2. fission
  3. endocytosed vesicle joins the early endosome compartment and is routed to other destinations
    a. recycling- basolateral domain of plasma membrane
    b. transcytosis- to apical domain of plasma membrane
    c. degradation (to lysosome)
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9
Q

explain how cells collect resources through endocytosis

A
  • endocytosis
  • uncoating of clathrin
  • fusion with endosome
    A.
  • budding off of transport vesicles
  • return of receptors to plasma membrane

B.

  • low pH causes separation and degradation
  • trans-cytosis if moved to other side of the cell
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10
Q

fusion

A

when vesicles merge or fuse with ANY membrane

- SNARE proteins specify which membranes fuse and conduct the process

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11
Q

invagination

A

making ANY vesicles you invaginate go into the cytosol

  • makes an indent in the membrane
  • driven by clathrin

coat assembly and cargo selection –> bud formation –> vesicle formation –> uncoating

  • also driven by COPI and COPII
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12
Q

budding

A

indent out of the cell and taking some membrane with it

  • how some viruses leave the cell
  • driven by the ESCRT complex

ESXRT-0 –> ESCRT-1 –> ESCRT-II –> ESCRT-III (builds up around proteins, causing binding to occur) –> ESCRT-III

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13
Q

SNARE proteins

A

v-SNARE on the vesicle bind
t-SNARE on the target membrane
- bind to specific SNAREs

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14
Q

clathrin triskelion

A

clathrin molecule made of 3 heavy chains and 3 light chains

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15
Q

dynamin and fission

A

dynamin drives fission after vesicle invagination events

- dynamin is necessary to finish clathrin-coated vesicles

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16
Q

cargo is regulated by

A

signal sequences/moieties

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17
Q

transport machinery is regulated by

A
  • signaling lipids (PIPs)
  • small GTPases
  • other mechanisms
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18
Q

phospholipid changes

A
  • inositol sugar head can be phosphorylated
  • phosphotases and kinases add/remove phosphate groups at different positions of the ring to make a variety of phosphoinsositide (PIP) species
  • each PIP binds to specific proteins
    • protein partners are recruited to the sites PIPs are found at in the trafficking network
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19
Q

activation of GTPases

A
  • active in the GTP-bound state
  • localized in the cell
  • bind and activate downstream effectors
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20
Q

rab11 location

A

recycling endosomes

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21
Q

rab5A location

A

plasma membrane, clathrin-coated vesicles, early endosomes

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22
Q

rab7

A

late endosomes

23
Q

rab functions

A
  • recruited to specific membranes by RabGEFs
  • activation promotes downstream effects
  • specific Rab works with specific PIP
24
Q

2 main tissue categories

A
  1. epithelial tissue
    - lines surface cavities
    - surrounds organs
    - cells directly connected
    - mechanical stresses are transmitted from cell to cell by cytoskeletal filaments anchored to cell-matrix and cell-cell adhesion sites
  2. connective tissue
    - cells dispersed
    - a lot of ECM provides overall structure
    - ECM directly bears mechanical stresses of tension and compression

both are separated by the basal lamina (specialized ECM)

25
Q

occluding junction

A

APICAL

tight junction seals gap between epithelial cells

26
Q

cell-cell anchoring junctions

A

APICAL

  • adherins junction connects actin filament bundle in one cell with that in the next (DO NOT go through the junctions)
  • desmosome connects intermediate filaments in one cell to those in the next cell (DO NOT go through the junctions)
27
Q

channel-forming junctions

A

BASAL

gap junctions that allow the passage of small, water-soluble molecules from cell to cell

28
Q

cell-matrix anchoring junctions

A

BASAL
- actin-linked cell-matrix adhesion anchors actin filaments in ell to extracellular matrix

  • hemidesmosome anchors intermediate filaments in a cell to ECM
29
Q

adheren junction structure

A
  • form strong continuous adhesion belts

- adhesion mediated by cadherin clusters

30
Q

cadherin mediate through:

A
  1. homophilic interactions
    - 38.5nm
    - C-terminal on outside; N on inside
    - Ca2+ keeps rigid for proper adhesion
  2. links to the actin cytoskeleton
    - linked by a chain of catenin and other anchor proteins
31
Q

adheren function

A

tissue maintenance during development
- tissue structure is lost in adherens junction mutants

tumour suppression
- loss of epithelial structure is a hallmark of cancer

32
Q

apical and basal sides

A
  • apical faces the lumen or animal surface
  • basal faces underlying tissue
  • creates polarity for organ function
33
Q

importance of polarity

A

controls the solute diffusion between our body compartments

  • molecules are blocked from diffusing between cells by tight junctions
  • must be actively transported through cells by plasma membrane channels allowing for precise regulation
34
Q

what would happen without tight junctions?

A
  • molecules can travel back and forth
  • membrane proteins could diffuse
  • passive carriers diffuse to apical side
  • loss of polarity
35
Q

how are tight junctions formed

A
  • formed by the interaction of transmembrane proteins

- these pass through the cell 4 times

36
Q

core tight junction proteins

A
  1. claudin

2. occludin

37
Q

what movements do tight junctions block?

A
  • movement of aqueous molecules through the extracellular space b/w cells
  • movement of membrane molecules between the apical and basolateral domains of each cell’s plasma membrane
38
Q

how is polarity established

A

cells use landmarks (type of signal or structure) to establish and elaborate polarity

39
Q

what do chemoattractants do?

A

polarize cells

- bind to a receptor causing both actin polymerization and actin-myosin contraction

40
Q

microtubules

A
  • 13 parallel protofilaments forming a hollow cylinder

- inherently polarized

41
Q

protofilaments

A
  • made of heterodimers of alpha and beta-tubulin
  • each heterodimer is asymmetric
  • both bind to GTP
  • they assemble head to tail to form polarized filaments
42
Q

how do gamma-tubulin complexes nucleate microtubules

A
  • binds tubulin heterodimers to assemble protofilaments into tubes
  • gamma-tubulin nucleates microtubules at their minus ends
  • plus ends grwo away from nucleation sites
  • gamma-tubulin often associates with large microtubule organizing centres
43
Q

the centrosome

A

contains 2 centrioles surrounded by hundreds of proteins with gamma-tubulin nucleation sites on the surface

44
Q

dynamic instability (definition)

A

single microtubules switch between growing and shrinking

- allows microtubules to search the cytoplasm

45
Q

dynamic instability (process)

A
  • growing microtubules have a protective cap of GTP-bound tubulin
  • plus sides bind to each other
  • rapid growth with GTP-capped end
  • loss of GTP cap
  • rapid shrinkage
  • regain of GTP cap
  • rapid growth with GTP-capped end
46
Q

how is motor activity polarized?

A
  • dynein moves to microtubule, minus ends to nucleus

- inesin moves to microtubule, plus ends away

47
Q

what is a likely key for golgi positioning?

A

dynein

48
Q

actin skeleton- cell structure and behaviour

A
  • actin skeleton is inherently polarized from subunit, to filaments, to networks
  • actin monomers are asymmetric
  • actin monomers bind and hydrolyze ATP
  • actin monomers assemble head to tail forming polarized filaments
49
Q

ATP-ADP polarity in actin cytoskeleton

A
  • after polymerization, Actin-ATP –> Actin-ADP
  • hydrolysis reduces binding affinities to neighbouring subunits increasing dissociation
  • rate of addition of Actin-ATP > rate of removal of Actin-ADP –> a cap of Actin-ATP can be formed
50
Q

treadmilling

A

maintaining a constant length with a flux of subunits through the filament

  • subunits can undergo net assembly at + end (=/> net disassembly at - end) because of the polarity
  • requires traction to drive cells forward
51
Q

how is the i end stabilized

A

the actin-related protein (ARP) complex nucleates actin filaments

  • actin filaments are branched to form polarized 2-D networks
  • positive at the top (ATP addition)
  • negative at the bottom (ADP loss)
52
Q

how does treadmilling produce protrusive power

A
  • whole networks and single filaments can both treadmill
  • net filament assembly at leading edge and disassembly behind leading edge
  • caused by diffusion of actin monomers
53
Q

creating protrusive machines from treadmilling microfilaments

A
  • stationary anchor binds one part of the filament
  • treadmilling filament extends from that point
  • extension pushes against the cell membrane driving cell protrusion
  • protrusive machines are created by anchoring large regions of actin networks
  • active filaments hook to transmembrane protein to push against ECM
54
Q

integrins connect the ____________ to ___________

A

integrins connect the actin cytokeleton to extracellular matrix molecules

  • main receptors that bind extracellular molecules
  • transmembrane heterodimers of non-covalently associated alpha and beta subunits
  • linked to the actin cytoskeleton via adapter proteins

BIO230 (4 decks)

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