cellular interaction cellular interactions
Transcript of cellular interaction cellular interactions
cellular interactions
chapter 20
tissues• cellular interaction
• in some organisms, cells interact to form defined tissues
• extracellular matrix• allows for cellular
interaction• extremely important in
certain tissues• connective tissue• epithelial tissue
epid
erm
isde
rmis
extracellular matrix• ECM -
• present in pretty much all animals• evolved in some ancestor of the animals
• sponges• mesohyl • basic ECM elements
• type IV collagen• spongin
• laminins• what about plants?
• special ECM• cell wall matrix
ECM fibers• collagens
• fibrous glycoproteins• most abundant protein
in humans• very strong• structure
• triple helix• arranged in
staggered array• overlap 25%
3 helical polypeptides (sinistral)
collagen molecule (dextral triple helix)
overlapping collagen fibril
mature collagen fiber
ECM fibers• collagens
• types I-XIX• I-III most common in humans• IV - not fibrillar
• spongin matrix in sponges• cuticle of nemata• bone• cartilage• type III - reticular fibers
• branching network
collagen problems• collagen-related diseases
• type I (osteogenesis imperfecta)
• type II (dwarfism)• type IV
• Alport syndrome• kidney disease
(glomerular nephritis)• blindness (ocular lesions)• hearing loss
• Ehlers-Danlos syndrome• hyperflexibility / extensible
skin
ECM fibers• elastic fibers
• elastin• cross-linked into network
• provide elastic strength• important for organs that stretch
elastic fiber
fibronectin• fibronectin structure
• glycoprotein found in nearly all animal connective tissue • two nearly identical polypeptides• can bind to cells and ECM
COOH
COOH
H2N
H2NFibrin-binding domains
heparin-binding domain
cell-binding domain
collagen-binding domain
S-S S-S
cell interaction• integrins
• receptors with α and β subunits• each with several domains• many possible
configurations of 26 known subunits
• contain relatively short transmembrane domain
• conformations• inactive - bent• active - unbent / legs apart• can adopt many different
active configurations
α subunitβ subunit
β-propellerβ-I domain
αI domain
interaction with cells• integrins
• cell-binding sites in extracellular proteins• RGD - (arginine-glycine-aspartic acid) recognized• integrin binds with RGD sequence
• two main functions• adhesion of cells to substrate• transmission of signals from external environment
• β subunits• three main classes: β1, β2, β3
• clotting• fibrinogen (RGD sequence) binds to integrin• clot busters - competitive inhibitors
proteoglycan complexes• proteoglycans
• core protein• GAGs (glycosaminoglycans)
• repeating disaccharide structure• cushion cells, help resist crushing
laminin• laminins
• glycoproteins - triple helix (like collagens)• many diverse forms (little homology)• form web-like networks
• resistant to tensile force
basement membrane• basement membrane
• basal lamina• flattened layer of ECM
• ECM secreted by fibroblasts• reticular layer
• lamina reticularis - reticular fibersepithelial cellshemidesmosome
basal lamina
reticular lamina
basement membrane• basal lamina
• 4 main functions• structural foundation for
epithelium• selective membrane• facilitate access to proteins• serve as guide for
developing neurons
basal lamina• Collagen IV • Laminins• Nidogens (entactins)• Perlecan
(proteoglycan)
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collagens - (glycoprotein) - dextral triple helix of 3 sinistral
alpha helices - high tensile strength - lots of kindselastic fibers - cross-linked networks of elastin
and fibrillin - allow organs to stretch and recoilproteoglycans - - huge protein-GAG complexes - serve as cushioning - form hydrated gelsfibronectin - (glycoprotein) - two identical polypeptides -
homodimer - bind to integrins - can bind to cells and to ECM fibers - important in migration of cells
- anchors cells to proteoglycans or collagen
laminins - (glycoprotein) - triple helix of 3 linked polypeptides - high tensile strength - along with collagen IV, comprises
basis for basal laminaentactin - (glycoprotein) - connects collagen and laminin
networks - web of collagen IV and laminins
connected by entactinintegrins - - heterodimers - attached to PM - bind to various ECM elements - act as cell receptors
cell-ECM junctions• hemidesmosomes
• different class - β4
• link to intermediate filaments• dense plectin plaque
• linked to ECM by integrins • can be disassembled and
reassembled
cell-cell junctions• junction complex
• found on lateral aspect of plasma membranes
• comprise several types of junctions• tight junctions
• function• paracellular transport• creates membrane polarity:
apical, basal• membrane domains• prevent movement of proteins
between domains
cell-cell junctions• tight junctions
• complex collections of proteins• transmembrane proteins
• claudins• occludins• junctional adhesion molecule (JAM)
• polarity proteins• cytoskeletal proteins• signaling proteins
cell-cell junctions• adherens junctions
• link adjacent cells• located just basal to tight
junctions• transmembrane receptor
proteins• cadherin dimers
• bind to identical cadherins on neighboring cells
• anchor proteins (catenins)• link to actin bundles
cell-cell junctions• septate junctions
• only in invertebrates• similar in function to tight junctions• located basal to adherens junctions
cell-cell junctions• desmosomes
• cytoplasmic plaques• inner dense plaque• outer dense plaque• connected to
intermediate filaments• main function:
• link cells together• important for cells
exposed to physical stress
cell-cell junctions• junction complexes
• tight junctions• adherens junctions• desmosome• hemidesmosome• (gap junction)
cell-cell communication
hydrophilic channel
cell membrane
cell membrane
cytoplasm
cytoplasm
connexon• gap junctions• analagous to
plasmodesmata• vertebrates
• connexon (2)• connexins (6)
• invertebrates• innexon (2)
• innexins (6)
cell-cell communication• plasmodesmata
• intercellular cytoplasmic channels • desmotubule
• trapped portions of ER• passage of materials limited
• size constraints• interconnect protoplasts
• symplast cell wall
plasma membrane
Cell wall
Microfibril
Cellulose microfibrils in a plant cell wall
Cellulose molecules
β Glucose monomer
10 μm
0.5 μm
plant cell walls • comparative cell wall composition
• for bacteria - mainly peptidoglycan• for fungi - chitin• for plants cellulose
• cell wall matrix• microfibrils• proteins• pectin• hemicelluloses
cell wall matrix• microfibrils
• arranged in radial arrangement• restrict cell expansion
• cell elongation• influx of water
• increases cell volume• added by cellulose synthase
Cellulose microfibrils
Nucleus
Elongation
Vacuoles
5 µm
microtubule
cellulose synthase complex
microfibril
cell wall matrix• composition of cell wall
matrix• hemicellulose
• highly branched• crosslinked to microfibrils
• pectin• negatively charged
galacturonic acids• form a gel
• microfibrils• glycoproteins
pectin
cellulose microfibril
hemicellulose
soluble protein
• layers• middle lamella (outer layer of pectin)• primary cell wall
• more flexible, laid down first • secondary cell wall
cell wall matrix
middle lamella
plasma membrane
primary cell wall
cell wall matrix• lignin
• used to stiffen and strengthen cell walls• 2nd most abundant organic polymer• hydrophobic polymer
• p-coumaryl alcohol • coniferyl alcohol• sinapyl alcohol