Cell Junctions and the Extracellular Matrix Flashcards
What do cellular junctions link together?
- Cells together
- Attaches cells to extracellular material
~ does so through cytoskeleton
What do tight junctions do?
= occluding junction
- Form a network around the apical surface
- Composed of two membrane proteins= Claudin and Occludin
What do Claudin and Occludin do?
Link to actin cytoskeleton via adaptor protein (ZO-1)
For tight junctions, can tracers injected into gut or between basolateral surfaces of cells pass?
NO
How do tight junctions maintain polarity of epithelia?
- Physically separate apical and basolateral surfaces
- Contents of the intestine must pass through cells
Adherens junctions
= anchor adjacent cells
Cadherins
Transmembrane proteins that span the gap between cells
What link cadherins to actin filaments inside the cell?
alpha and beta catenin
During Adherens Junctions, what is it called when a ring forms around epithelial cell in a layer?
Adhesion belt
Desmosomes
= anchor adjacent cells
Cadherins
span inter membrane space
- attach to an intracellular “plaque” attached to intermediate filaments (keratin to skin)
What kinds of tissues are desmosomes most prevalent in?
Tissues subject to mechanical stress
(ex. skin, gut, epithelium, muscle, etc.)
Hemidesmosomes
= attach cells to basal lamina
- resemble half of a desmosome
- composed of integrins
What do integrins do?
Link intermediate filaments (keratin) to basal lamina (collagen)
Gap junctions
= create aqueous pores between cells
- allows chemical communications between cells in a tissue
Connexins
span membrane/interact with those of adjacent cells (connexon hexamer)
What do connexins do?
causes gap junctions to open or close
- ex. closes in response to increase in Ca2+ (calcium) released by ER; happens when cell is damaged
Tight junctions!
Function: seal spaces between cells
Transmembrane proteins: Caudin & Occludin
Cytoskeleton attachment: Actin (through ZO-1)
Adherens junctions!
Function: Cell-cell anchoring
Transmembrane proteins: Cadherins
Cytoskeleton attachment: Actin (through alpha and beta catenin)
Desmosomes!
Function: Cell-cell anchoring
Transmembrane proteins: Cadherins
Cytoskeleton attachment: Intermediate filaments
Hemidesmosomes!
Function: anchor cell to basal lamina
Transmembrane proteins: Integrins
Cytoskeleton attachment: Intermediate filaments
Gap junctions!
Function: cell-cell communication
Transmembrane proteins: Connexin (Hexamer=Connexon)
Cytoskeleton attachment: none
Tissues
collection of similar cells that perform a limited number of specialized functions
What are the four basic types of tissues?
1.) Muscle
2.) Nervous
3.) Epithelial
4.) Connective
What are the two surfaces of epithelial tissue?
1.) Apical surface
2.) Base/Basal lamina
Apical surface
faces exterior body or internal space
Base/Basal lamina
attached to adjacent tissues
- Mostly collagen and laminin
- Separates epithelia from connective tissue
Connective tissue
involved in cell movement, differentiation, and communication
- produces the extracellular matrix (ECM)
3 basic components of connective tissue
1.) Extracellular protein fibers
2.) Ground substance (fluid)
3.) Specialized cells
Extracellular protein fibers
Give tensile strength
- Ex. collagen, laminin, fibronectin, etc.
Ground substance (fluid)
resists compression
Specialized cells
- Ex. fibroblasts, macrophages, mast cells, etc.
ECM forms scaffold for building organs
Removal of cells using detergent= “organ ghost” (remaining ECM)
- can repopulate with donor cells= heart starts beating again
What is the most abundant protein in animals (30%)
Collagen
What is synthesized in the RER in fibroblast cells
Procollagen
Collagen
molecules form a triple helix held together by hydrogen bonds
What self assembles in extracellular space in a staggered fashion, forming fibrils
Collagen
- often arranged at right angles to increase tensile strength
Fibrils associate to form what?
fibers
- crosslinks give added strength
What links cell to ECM (hemidesmosomes)
Integrins
- anchored to actin filaments inside the cell
Fibronectin
Protein in ECM bound to collagen
- Integrins bind to fibronectin
- Most cells prefer to grow when in contact with fibronectin/ECM
When do most cells prefer to grow?
when in contact with fibronectin/ECM
