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BIOC 341 > Lecture 23: Cell Junctions and Cell Adhesions > Flashcards

Lecture 23: Cell Junctions and Cell Adhesions Flashcards

1
Q

How is stress transmitted in epithelial tissue vs connective tissue?

A
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2
Q

4 Types of cell junctions in animal cells?

A
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3
Q

Anchoring Junctions

A

– Include cell-cell and cell-matrix interactions

– Transmit external stress from across the plasma membrane to the underlying cytoskeleton

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4
Q

Occluding Junctions

A

– Form a permeability barrier between cells in an epithelia sheet

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5
Q

Channel forming Junctions

A

– Create cytoplasmic continuity between adjacent cells for the passage of small molecules

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6
Q

Signal Relay Junctions

A

– Allows extracellular signals to be passed from one cell to another

– Some anchoring junctions and channel forming junctions also conduct signaling

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7
Q

adherens junctions and desmosomes are ___

A

cell-cell anchoring junctions

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8
Q

actin-linked cell matrix junctions and hemidesmosomes are____

A

cell-matrix anchoring junctions

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9
Q

tight junctions are ___

A

occluding junctions

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10
Q

Gap junctions are ___

A

channel forming junctions

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11
Q

tight junction

A

seals gap between epithelial cells

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12
Q

adherens junction

A

connects actin filament bundle in one cell with that in the next cell

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13
Q

desmosome

A

connects intermediate filaments in one cell to those in the next cell

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14
Q

gap junction

A

allows the passage of small water-soluble molecules from cell to cell

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15
Q

actin-linked cell-matrix junction

A

anchors actin filaments in cell to extracellular matrix

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16
Q

hemidesmosome

A

anchors intermediate filaments in a cell to extracellular matrix

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17
Q

_____ link the cytoskeleton to extracellular structures

A

Transmembrane proteins

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18
Q

Cell-cell interactions are mediated by the ____ family of transmembrane anchors

A

cadherin

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19
Q

Cell-Matrix interactions are mediated by the ____ family of transmembrane anchors

A

integrin

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20
Q

Anchoring Junctions function

A

• Provide mechanical strength

– Especially important to tissues encountering severe mechanical stress like heart, muscle, and skin

• Connect the cytoskeleton to neighboring cells or the extracellular matrix

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21
Q

Anchoring Junctions are composed of what two main classes of proteins?

A

– Intercellular anchor proteins

– Transmembrane adhesion proteins

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22
Q

Types of Anchor Junctions

A

– Adherens junctions

– Desmosomes

– Hemidesmosomes

– Focal Adhesions

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23
Q

Cadherins

A
  • Ca2+-dependent cell-cell adhesion
  • Present in adherens junctions and desmosomes
  • Found in virtually all cells and tissues
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24
Q

Cadherin superfamily

A
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25
Q

Cadherins mediate ____ adhesion

A

homophilic

26
Q

Cadherin structure and function

A
27
Q

How do cadherins play a role in development?

A

Cell with similiar subclasses of cadherins expressed on their surface stick together because of homophilic binding

28
Q

Cadherins mediate cell-cell adhesion by a homophilic mechanism

A

• Tissue culture cells (that normally do not express N or E-cadherins) can be made to express either N- or Ecadherin.

• The resulting population self selects based on homophilic interaction of the individual cadherins

29
Q

Which proteins link cadherins to actin filaments?

A
  • p-120 catenin
  • Beta-catenin
  • Alpha-catenin
  • vinculin
30
Q
A
31
Q

Adherens junctions

A
  • Connect bundles of actin filaments between cells
  • Can form adhesion belts (zonula adherens) in epithelial layers
  • Transmembrane adhesion proteins belong to the cadherin family
  • Intracellular anchoring proteins

– Catenins

– Vinculin

– α-actinin

• Cells must be attached by adherens junctions for tight junctions to form

32
Q

Adherens junctions structure

A
33
Q

Early formation of adherens junctions

A
34
Q

Mechanotransduction in an adherens junction

A
35
Q

Uses of adherens junctions in development

A
36
Q

Desmosomes

A
  • Connect intermediate filaments between cells
  • The type of intermediate filament attached is cell type specific

– Keratin filaments in most epithelial cells such as skin

– Desmin filaments in heart muscle

37
Q

Transmembrane adhesion proteins of desmosomes belong to the cadherin family:

A

– Desmoglein

– Desmocollin

38
Q

Intracellular anchoring proteins of desmosomes?

A

– Plakoglobin (γ-catenin)

– Desmoplakin

– Plakophilin

39
Q

Desmosome Model

A
40
Q

Hemidesmosomes

A
  • “Half desmosomes” that connect intermediate filaments to the basal lamina
  • Morphologically similar to desmosomes Transmembrane adhesion proteins belong to the integrin family

– Extracellular domain of the integrin binds to laminin (more later)

• Intracellular anchor protein

– Plectin

41
Q

Desmosomes and hemidesmosomes link to the ____ network

A

intermediate filament

42
Q

____ mediate transient cell-cell adhesions in the bloodstream

A

Selectins

43
Q

Selectins

A

– Cell surface, carbohydrate binding proteins (lectins) – Ca2+-dependent cell-cell adhesion

– L-selectins

• While blood cells

– P-selectins

• Platelets

– E-selectins

• Activated endothelial cells

44
Q

The structure and function of selectins

A
45
Q

Cell Adhesion Molecules (CAMs)

A

• Cell surface transmembrane proteins

– Cell-cell adhesion

– Cell-matrix adhesion

  • Some are Ca2+-dependent, while others are Ca2+- independent
  • Initially identified using antibodies to cell surface molecules
  • Antibodies to key CAMs were capable of inhibiting cell-cell adhesion in the test tube
46
Q

Ig superfamily Cell Adhesion Molecules (CAMs) structure

A
47
Q

Tight Junctions

A
  • Occluding junctions in vertebrates
  • Also known as Zonula occludens (ZO)
  • Provide a barrier role in most epithelia
  • Prevent protein and lipid diffusion in the plasma membrane allowing for polarization

– Apical vs. basolateral membrane

• Variable permeability barrier between cells

– Cell type dependent, bladder epithelial tight junctions are 104 X less permeable to inorganic ions like Na+ than intestinal epithelia

48
Q

Tight junction model

A
49
Q

What are the tight junction proteins?

A

claudin and occludin

50
Q

Claudin and occludin also bind to peripheral membrane proteins called ___ proteins that anchor the sealing strands to the actin cytoskeleton

A

ZO

51
Q

ZO proteins form ____ at tight junctions

A

scaffolds

52
Q

Septate Junction

A

Occur in invertebrates like Drosophila Functionally similar to tight junctions Different in structure and appearance

53
Q

Gap junctions

A
  • Most cells in most tissues are in communication with neighboring cells by gap junctions
  • Made up of membrane-spanning channel-forming proteins called connexins
  • The channels or connexons have a maximal pore size of ~ 1.5nm
  • Allow the passage of small molecules but not proteins

– Inorganic ions, sugars, amino acids, nucleotides, etc

54
Q

Anatomy of Gap junctions

A
  • Each connexin monomer has four membranespanning segments
  • Humans have 14 different connexin genes
  • Six monomers assemble into a connexon
  • Different connexin subunit assemblies can produce different connexons
  • Connexons from adjacent cells interact to form an intercellular channel
55
Q

Gap junction diagram

A
56
Q

Structure of Gap Junction

A
57
Q

Gap junctions have diverse functions

A

• Electrical synapse

– Direct coupling allows the propagation of an action potential from one cell to another without the need for a chemical intermediate (much faster)

• Sharing of metabolites helps coordinate activities

– Glycogen breakdown in response to hormonal stimulation in the liver

– Hepatocytes not directly stimulated by hormone (potentially several cell layers away from a capillary and the source of the hormone) detect a signal by sharing a second messenger through gap junctions

• Communication during development

58
Q

Connexin turnover

A

Connexins are added to the edges and removed from the middle

59
Q

Regulators of gap junction permeability?

A

– pH
– Cytosolic Ca2+ concentration
– Extracellular signals
• Some neurotransmitters like dopamine

60
Q

Why regulate gap junction permeability?

A

– Cells need a way to close down these connection to prevent widespread damage when one participant is damaged

61
Q

Plasmadesmota

A

“Plant Gap Junctions” Since plants have a rigid cell wall, a specialized structure is required to bridge it

BIOC 341 (24 decks)

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