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Molecular BIO > 22 Cell Junctions > Flashcards

22 Cell Junctions Flashcards

1
Q

Connective tissue

A

bone, tendon with plentiful extracellular matrix and cells with minimal distribution throughout

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2
Q

Epithelial tissue

A

cytoskeleton of cells form anchoring junctions. mostly consistent of basal lamina

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3
Q

Cell-matrix

A

bon epithelial tissue to connective tissue

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4
Q

What are the four types of cell junctions?

A
  1. anchoring
  2. occluding
  3. channel-forming
  4. signal-relaying
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5
Q

Anchoring junction

A

cell-cell adhesion and cell-matrix adhesion connected to cytoskeletal filaments inside cell

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6
Q

Occluding junctions

A

closes gaps between epithelial cells

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7
Q

channel-forming junctions

A

passageway for small, water-soluble ions

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8
Q

Signal-relaying junctions

A

allow signal relay-between cells

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9
Q

Actin filaments participate in what attachment sites?

A
  1. adherenes (cell-cell)

2. actin-linked cel-matrix adhesions ( cell-matrix)

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10
Q

Intermediate filaments participate in what attachment sites?

A
  1. desmosomes (cell-cell)

2. hemidesmosomes (cell-matrix)

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11
Q

What is the role of transmembrane adhesion proteins?

A
  1. anchoring junctions that span membrane, extending from cytosol to ECM
  2. cadherins or integrins, selectins, Ig superfamilies
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12
Q

A classical cadherin is seen where?

A
  1. adherens (cell-cell) junctions with actin filaments
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13
Q

A nonclassical cadherin is seen where?

A
  1. desmosomes with intermediate filaments
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14
Q

Integrins are commonly found where?

A
  1. actin-linked cell-matrix adhesions with actin filaments
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15
Q

Cadherins are what?

A
  1. Ca ion dependent cell adhesion
  2. classical: form adherens junctions
  3. E-cadherin: epithelial cells and brain
  4. nonclassical: desmocollins/desmogleins that form desmosome junction
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16
Q

Do cadherins bind homo or heterophilically?

A

homophilic ir preferred but heterophilic can occur

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17
Q

What does the presence/absence of Ca ion play in cadherins?

A
  1. Ca present: binds in between the cadherins and increases rigidity of structure, preventing flexion
  2. Ca absence: allows cadherin repeats to flex and bend
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18
Q

Cadherins have low affinity for their ligand, so how do they form strong attachments?

A
  1. increase number of sites that are bound.

2. act like velcro

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19
Q

Sorting out

A
  1. promotes cadherins, homophilic binding ability via segregation
  2. provides ability for different tissue formation during development
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20
Q

Cadherins contain intracellular domains that allow what to attach?

A
  1. beta-catenin, p120-catenin, gamma-catenin which provide a link between the cadherin and actin filaments
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21
Q

A contractile bundle of actin filaments lies adjacent to and adhesion belt in what structure?

A

adherens junctions, which shapes multicellular structures

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22
Q

What is the role of desmosomes?

A
  1. mechanical support that binds to intermediate filaments
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23
Q

What is the structure that provides desmosomes the ability to bind strongly to one another?

A
  1. plaque surface of multiple proteins that side-by-side interaction allow for mechanical strength
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24
Q

desmoglein/desmocollin

A
  1. homo-/heterophilic binding to the inner dense plaque.
  2. are transmembrane and form the outer dense plaque
  3. bind to a belt of plakophilin and plakoglobin
25
Q

True/False

The cell type determines the type of intermediate filament that is formed?

A

true

26
Q

Tight junctions

A
  1. seals gap between cells
  2. forms fence between membranes
  3. recruits cytoskeleton and signaling molecules
27
Q

Why do tight junctions appear as fusion of PMs?

A
  1. focal connections between two PM correspond to connected sealing strands
28
Q

What are two important proteins that help form tight junctions?

A
  1. claudin (main function)
  2. occludin
  3. consist of 4 TM domains, C-/N- terminus are intracelular for signaling probably
29
Q

What protein is responsible for controlling the position and organization of tight junctions?

A
  1. ZO (Tip protein family)

2. controls anchoring of tight junctions to actin cytoskeleton

30
Q

Barrier junction

A

tradition thought of tight junction, but have diversified permeability. is extracellular

31
Q

Fence junction

A

in the PM, that encircle the individual cells between apical and basolateral membranes.
- limit lateral diffusion

32
Q

Signaling function of tight junctions

A

cytoplasmic region only. activate PDZ-containing proteins

33
Q

What proteins are responsible for establishing cell polarity?

A
  1. Par
  2. Crumbs
  3. Scribble
34
Q

How is epithelial cell polarity established?

A
  1. E-cadherins cluster, at cell-cell junction
  2. AJ, TJ recruited to site of adherance
  3. Par complex recruited to primitive adhesions to promote Par3-Par6-atypical protein kinase C assembly
35
Q

What is the role of Par complex in adhesion formation?

A
  1. par complex leads to activation of Crumbs and Scribble complexes to form other junctions
36
Q

Where is Crumbs-3 mostly expressed?

A
  1. epithelial cells as an apical membrane determinant
37
Q

is the scribble complex intra- or extra cellular?

A

intracellular

38
Q

What is able to cause a gap junction to rapidly close that gated-channel?

A
  1. rapid influx of Ca into a damaged cell, to isolate and protect other cells
39
Q

What extracellular macromolecules are associated with the basal lamina?

A
  1. fibrous protein(glycoproteins)

2. glycosaminoglycans (generally combine to form proteoglycans)

40
Q

What is the basal lamina made of?

A
  1. collagen type IV
  2. laminin
  3. nidogen
  4. perlecan
41
Q

Laminin.

A
  1. alpha, beta, gamma
  2. primary organizer of sheet
  3. contain multiple bind sites for variety of compounds
42
Q

Type IV collagen

A
  1. provide tensile strength to basal lamina
  2. consist of 3 super-twisted alpha helices
  3. bind with laminin to form 2-D sheet
43
Q

Nidogen and perlecan

A
  1. linkers to connect laminin and Type IV collagen
44
Q

What are integrins and dystroglycans used for in the basal lamina?

A
  1. TM receptors

2. holds laminin feet to allow for coordination of other basal lamina components

45
Q

What is the function of the thick basal lamina in the glomerulus of the kidney?

A
  1. prevent macromolecule passage into blood

2. based on GAGs function as a filter

46
Q

How can the basal lamina act as a selective barrier for cell movement?

A
  1. prevents fibroblast in CT to contact epithelial tissue

2. permeable to macrophages, neutrophils, and proteases

47
Q

What role does the basal lamina have in tissue regeneration?

A
  1. acts as a scaffold for regenerative cells to adhere to and begin repair
48
Q

What is an important structural feature of integrins?

A
  1. short C-tail intracellularly, long N-terminal extracellularly
  2. alpha-beta heterodimer
49
Q

What intracellular protein is required to link the integrin tails to actin

A

talin, which binds to beta subunit

50
Q

What type of integrin is most prominent in hemidesmosome adhesion?

A
  1. alpha6beta4 which attaches to keratin filaments from plectin and dystonin
51
Q

What defects would be prevent to produce a skin blistering disease?

A
  1. loss of plectin, dystonin, alpha6beta4, causing loss of skin attachment to the basal lamina
52
Q

Outside-in activation of integrin

A
  1. ligand binds to the ECM region. causing conformatin change
  2. conformation shifts alpha-beta units further apart allowing talin to bind beta unit
  3. actin filament then bind to talin unit
53
Q

Inside-out activation of integrin

A
  1. PIP2 promotes translocation of talin to the beta subunit
  2. binds to beta chain, causing conformational separation of units
  3. causing extension of ECM region, increasing affinity for ligands
  4. under influence from other signaling methods of the cells. (GPCR, RTK,)
54
Q

What is the central signaling module downstream from integrins?

A

Src/FAK complex which causes ERK/JNK regulation for cell survival, proliferation, differentiation

55
Q

What is the function of Focal adhesion kinases?

A
  1. promote cell fluidity; breakdown focal adhesion

2. cancer have increased FAK, to provide higher level of mobility

56
Q

What are the different types of glycosaminoglycans?

A
  1. chondroitin sulfate
  2. dermatan sulfate
  3. heparan sulfate
  4. keratan sulfate
57
Q

What is the function of the glycosaminoglycans?

A
  1. mechanically support tissue and withstand compressive forces
  2. high cation concentration, attracts water to the area, providing resistance to compression
58
Q

The hydroxylases that are required to form precursors for collagen assembly, form what chemical?

A

generate hydroxyl groups for collagen assembly.

Molecular BIO (24 decks)

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