PHSL233 > 2. cell junctions > Flashcards

2. cell junctions Flashcards

(51 cards)

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1
Q

why are cell junctions important

A
  • anchors cells
  • controls paracellular pathway
  • resists shearing forces
  • assists communication
  • maintains cell polarity
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2
Q

communicating junctions

A

gap

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3
Q

occluding junctions

A

tight junctions

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4
Q

adhering junctions

A
  • zonula adherens
  • desmosomes
  • hemidesmosomes
  • focal adhesions
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5
Q

which junctions adhere to cytokeratin

A

desmosomes and hemidesmosomes

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6
Q

which junctions link to actin

A

most gap, tight, adherens, focal adhesions

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7
Q

order of cell junction complex formation

A
  • initiate cell-cell contact
  • adherens junctions
  • tight junctions
  • gap junctions as needed
  • desmosomes
  • hemidesmosomes and focal adhesions
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8
Q

what occurs during adherens junction assembly

A
  • e-cadherin clustering
  • actin remodelling
  • initiation of polarity
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9
Q

what happens during tight junction formation

A

recruitment and positioning of polarity determining complexes
- act as molecular landmarks
- includes recruitment of ZO-1

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10
Q

how big are gap membrane channels

A

1.5-2nm diameter

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11
Q

what is allowed through a gap junction

A

cytoplasm and small molecules
- eg. ions, ATP, second messengers (cAMP, IP3 etc) glucose amino acids etc

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12
Q

what is the function of gap junctions

A
  • bridges the gap between cells
  • allows for rapid bidirectional juxtacrine signalling
  • direct cytoplasmic exchange
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13
Q

what is a gap junction made of

A

two connexons/hemichannels from neighbouring cells docked together

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14
Q

what is a connexon made of

A

6 connexin proteins

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15
Q

connexin structure

A

4 transmembrane domains connected by extracellular loops
- EL interact with connexins from other cells to form the gap junctions

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16
Q

how does a connexon channel open

A

when it has correctly docked at another connexon

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17
Q

what do connexins bind to at the plasma membrane

A

scaffolding protein ZO-1

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18
Q

how are gap junctions formed

A
  • connexins synthesised in rER
  • connexins oligomerised to connexons in golgi
  • connexons trafficked and inserted into plasma membrane near existing junctional complexes
  • clusters of channels form plaques
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19
Q

what is the function of tight junctions

A

selective barrier
- controls paracellular transport
- maintains cell polarity
- involved in signalling

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20
Q

how do tight junctions control permeability

A

they’re made of a branching network of sealing strands
- more strands = less permeable

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21
Q

transmembrane proteins in tight junctions

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A
  • occludin
  • junctional adhesion molecules
  • claudins
22
Q

scaffolding proteins in tight junctions

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A

link tight junctions to actin cytoskeleton
- includes ZO-1, ZO-2, ZO-3

23
Q

occludin

Study These Flashcards
A
  • 4 transmembrane domains
  • important for stability and integrity
  • contributes to tightness of tight junctions, not permeability
24
Q

junctional adhesion molecules (JAMs)

Study These Flashcards
A
  • transmembrane immunoglobulin proteins
  • mediate cell-cell adhesion
  • organise assembly
  • interact with cytoskeleton, signalling proteins, and scaffolding proteins
25
claudins
- 4 transmembrane domains - act as selective channels
26
claudin isoforms
~23 genes encode isoforms each allows/restricts particular ions or molecules based on tissue needs
27
claudin-1
blocks most ions and water - important in skin to prevent water loss and dehydration
28
claudin-2
selectively permeable to Na+, K+, Ca++, water - important in the nephron and intestines for absorption and reabsorption
29
tight junction formation
- initiated by adherens junctions - recruitment of polarity proteins - claudins and occludins inserted into apical membrane - JAMS dimerise and stabilise junction - ZO-1 binds to claudins, occludins, and f-actin - forms continuous circumferential belt
30
tight junction dysregulation
- inflammatory bowel disease - invasive and metastatic GI cancers - impaired reabsorption - salmonella
31
inflammatory bowel disease
- reduced claudin 1& 2 - increased claudin 3 - causes leaky barrier
32
loss of claudin 4 & 7, and occludins
linked to invasive and metastatic GI cancers
33
claudin 16 and 19 mutations
impairs reabsorption of Mg++ and Ca++ - especially significant in the nephron
34
salmonella and tight junctions
effector proteins disrupt tight junctions and allow bacterial invasions
35
what is the function of adherens junctions
- strong cell-cell adhesion - mechanical adhesion and tensile strength - drives cell and tissue remodelling - involved in signalling and establishing cell polarity
36
adherens junctions proteins
transmembrane - e-cadherins intracellular - catenins
37
e-cadherins
epithelial calcium dependant adherent proteins - forms dimers with neighbouring cells - Ca++ dependant binding
38
catenins
link cadherins to actin cytoskeleton - involved in regulating stability and signalling
39
adherens formation
- cadherins on adjacent cells form homodimers (Ca++ dependant) - cadherin cytoplasmic tails recruit catenins - catenins connect actin - junctions form a continuous circumferential belt
40
desmosomes function
- spot-like junctions linked to cytokeratin - strongest mechanical adhesion - abundant where there is high mechanical/shearing force
41
desmosome formation
- desmogleins and desmocollins on adjacent cells form hetero and homodimers - cytoplasmic tails recruit plakoglobin - plakoglobin binds desmoplakin - desmoplakin connects to cytokeratin
42
desmosome structural components
- DIFC - transmembrane proteins-desmosomal cadherins - intracellular proteins
43
desmosomes cadherins
- desmogleins - desmocollins
44
DIFC
desmosomal intermediate filament complex - extracellular core - dense plaques
45
desmosome intracellular proteins
plakoglobin and desmoplakin
46
hemidesmosome function
- anchors epithelia to basement membrane
47
hemidesmosome proteins
transmembrane - integrin intracellular - plectin extracellular - laminin (lamina lucida) - interacts with collagen in the basal lamina
48
hemidesmosome formation
- integrin heterodimers inserted into basal membrane - binds laminin - integrin binds to plectin - plectin links integrin to keratin - hemidesmosomes cluster
49
focal adhesion function
- mediate cell connection to ECM - more plastic than hemidesmosomes - involved in cell migration and signalling
50
focal adhesion formation
integrins bind to ECM components (fibronectin and collagen etc) - recruitment of adaptor proteins - link to actin
51
focal adhesion structural components
proteins - integrins (transmembrane) - adaptor proteins (eg. talin) focal adhesion kinase (FAK) - regulates adhesion turnover
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