Topic 12 Flashcards
extracellular matrix (ECM)
fills spaces between cells and bind cells and tissues together
ECM composition
tough fibrous structural proteins embedded in ground substance
ground substance
gel-like polysaccharide material
specialized adhesion proteins
anchor cells to ECM
collagen
major structural protein of ECM; most abundant protein in animal tissue
The collagens are a large family of proteins containing at least ___ different members
27
collagen form…
straight fibrils and fibres and networks
4 basic categories of collagen
fibril forming, network forming fibril associated anchoring, and transmembrane
Type I collagen class
fibril forming
Type IV collagen class
network forming fibril associated
Basic structure of collagen
repeats of Gly-X-Y (where X is usually proline and Y is usually a hydroxyproline) to form triple helices.
hydroxyproline
stabilizes colagen triple helices
collagen fibrils
collagen triple helices line up in a staggered arrangement, and are cross-linked together
-assemble within ECM
procollagen
partially processed precursor of collagen from cell via ER/Golgi
collagen is secreted as subunits of _______ that then assemble into ____ and ____ outside of the cell
pro collagen, fibrils, fibres
type IV collagen
network forming collagen; numerous interruptions of helical regions making them more flexible and cross linked to networks
elastic fibers
found in connective tissues and abundant in organs that regularly stretch and return to shape (lungs)
elastin
principal protein of elastic fibres; cross-linked into a network by covalent bonds between side chains of lysine residues
GAGs; glycosaminoglycans
gel-forming polysaccharides that consist repeating units of disaccharides
proteoglycans
higher order structures of GAGs (covalently linked to proteins) un to 95% carbohydrate by weight
chondroitin sulfate
GAG attached to a core protein
larger proteoglycan aggregates
proteoglycans interact with hyaluronan chains to form “bottle brush structures”
matrix adhesion proteins
responsible for linking components of matrix to another and to surfaces of cells
fibronectin
dimeric glycoprotein; principle adhesion protein of connective tissues
laminin
principle adhesion protein of basal lamina; a heterotrimer with 3 subunits (alpha, beta, game); contain domains that allow it to bind to itself, cells, collagen, and proteoglycans
nidogen
protein that links laminin to collagen type IV
agrin
large proteoglycan of ECM
integrins
major cell surface proteins responsible for attachment of cells to ECM, anchors the cytoskeleton within the cell and provides linkage between intra and extra matrix, and serve as receptors that activate intracellular signalling pathways in response to signals within ECM
integrin domains
cytoskeletal binding in cytoplasm, ECM binding domain and signal receptor domain
focal adhesions
a type of cell-matrix junction that attaches a variety of cells, including fibroblasts, to the ECM; this type of integrin binding is reversible
hemidesmosomes
strongest type of cell-matrix junction; mediate epithelial cell attachments at which a specific integrin interacts with laminin in the basal lamina
integrins link the _____ directly to the ______________
ECM, cytoskeleton
focal adhesion vs hemidesmosomes
focal adhesions can be stable but turn over rapidly, hemispheres are very stable and long-term
3 categories cell-cell junctions
- stable adhesion junctions
- tight junctions
- gap junctions
stable adhesion junction types
adherens junction and desmosome
adherens junction
region of c-c adhesion at which actin cytoskeleton is anchored to plasma membrane; involves protein in adjacent cells known as cadherins
desmosome
strongest c-c junction; region of adhesion between epithelial cells at which intermediate filaments are anchored to plasma junction
tight junctions
ensure any molecules moving across the epithelial cell layer in either direction MUST move through the cell not between cells (therefore, cell can regulate it!!)
cadherins
link actin cytoskeleton of adjacent cells
desmoglein and desmocollin
a family of cadherins involved in desmosomes that link the cytoskeletons of adjacent cells
what separates apical and basal domains of plasma membrane?
tight junctions
gap junctions
open channels through plasma membrane that provide direct connection between cytoplasm of adjacent cells and allow for open flow of ions and small molecules (mechanisms to couple metabolic and electrical activity)
connexin
transmembrane proteins that form gap junctions
connexon
cylinder formed by six connexins in plasma membrane
