16.2 The Extracellular Matrix and Cell-Matrix Interactions Flashcards
most animal cells are embedded in an () that fills the spaces between cells and binds cells and tissues together
extracellular matrix
one type of extracellular matrix is exemplified by the thin, sheetlike () upon which layers of epithelial cells rest
basal laminae
EC matrix is most abundant in ()
connective tissues (e.g. tendons, cartilage, bone matrix)
the 3 major components of the EC matrix
- matrix structural proteins
- matrix polysaccharides
- adhesion proteins
matrix structural proteins are predominantly ()
collagens (type I and IV)
composed principally of a protein called elastin → cross-linked into a network by covalent bonds formed between side chains of lysine residues (similar to those found in collagen)
elastic fibers
elastic fibers are principally composed of a protein called ()
elastin
how are elastic fibers cross-linked into a network
cross-linked by covalent bonds formed between side chains of lysine residues
differences between various types of EC matrices result from both (1) and from (2)
- quantitative variations in the types of amounts of EC components
- modifications in their organization
similar to plant cell walls, EC matrices are composed of (1) embedded in a (2)
- tough, fibrous proteins
- gel-like polysaccharide ground substance
the major structural protein of the extracellular matrix; single most abundant protein in animal tissues
collagen
collagen is characterized by the formation of ()
triple helices
collagen triple helix domain consist repeats of the amino acid sequence ()
Gly-X-Y
in the collagen triple helix domain amino acid sequence Gly-X-Y, X is usually (1) and Y is usually (2)
- proline
- hydroxyproline
in the collagen triple helix, () is required in every third position in order for the polypeptide chains to pack together close enough to form the collagen triple helix
glycine
one of the fibril-forming collagens that are the basic structural components of connective tissues; most abundant type of collagen
type I collagen
after secretion, type I collagens assemble into () in which the triple helical molecules are associated in staggered arrays
collagen fibrils
collagen fibrils do not form inside the cell because they are synthesized as soluble precursors called ()
procollagens
procollagens contain () at both ends of the polypeptide chain; cleaved outside the cell to produce collagen
nonhelical segments
covalent cross-links between side chains of () residues help strengthen the fibrils (composed of type I collagen)
lysine and hydroxylysine
collagen fibrils further associate with each other to form (), which can be several µm in diameter
collagen fibers
network-forming collagen that forms the basal laminae
type IV collagen
type IV collagen is more flexible than type I collagen (that form fibrils), thus allowing it to (…)
assemble into 2D cross-linked networks instead of fibrils
other types of collagens form (), which link basal laminae to underlying connective tissues
anchoring fibrils
some collagens are () that participate in cell-matrix interactions
transmembrane proteins
fibrous structural proteins of the EC matrix are embedded in gels formed from polysaccharides called ()
glycosaminoglycans (GAGs)
glycosaminoglycans (GAGs) consist of repeating units of the ff. disaccharides:
- either N-acetylglucosamine or N-acetylgalactosamine
- acidic disaccharides (either glucuronic acid or iduronic acid)
with the exception of hyaluronan, sugars of GAGs are modified by the (1) → GAGs are highly (2)
- addition of sulfate groups
- negatively charged
like pectin, GAGs () to form hydrated gels → provide mechanical support to the EC matrix
bind cations and trap water molecules
moreover, () is the only GAG that occurs as a single long polysaccharide chain
hyaluronan
hyaluronan is synthesized at the PM by () (transmembrane protein)
hyaluronan synthase
() contain GAG chains covalently bonded to serine residues of a core protein; interact with hyaluronan to form large complexes in the EC matrix
proteoglycans
proteoglycans can consist of up to 95% () by weight
polysaccharide
() are responsible for linking the components of the matrix to one another and to the surfaces of cells
adhesion proteins
adhesion proteins are the major binding sites for ()
cell surface receptors
adhesion proteins interact with (1) and (2) to specify matrix organization
- collagen
- proteoglycans
prototype of adhesion proteins; principal adhesion protein of connective tissues
fibronectin
fibronectin is a () composed of 2 polypeptide chains (each containing about 2.5k amino acids)
dimeric glycoprotein
dimers of glycoprotein form fibronectin by cross-linking into fibrils by ()
sulfate bonds
how is fibronectin able to cross-link matrix components
it contains binding sites for both collagen and proteoglycans
in addition to binding sites for collagen and proteoglycans, fibronectin also contains a distinct site that is recognized by ()
integrins
principal adhesion molecules of the basal lamina
laminin
describe the structure of laminins
cross- or T-shaped heterotrimers; can self-assemble into meshlike networks
laminins are composed of 3 subunits
- long alpha main chain
- beta and gamma side “arms”
how do laminins link matrix components to one another and to the cell surface?
different laminin subunits have binding sites for cell surface receptors (e.g. integrins) and proteoglycans
binds to laminins and is tightly associated to type IV collagen
nidogen
major cell surface receptors responsible for the attachment of cells to the EC matrix
integrins
integrins are composed of 2 subunits (1), the former of which bind (2)
- alpha and beta
- divalent cations
how do integrins attach EC components to PM
they bind to short amino acid sequences present in multiple components of the EC matrix (including collagen, fibronectin, laminin, and proteoglycans)
moreover, () on cell surfaces can also bind to EC matrix components and modulate cell-matrix interactions
transmembrane proteoglycans
how do integrins also serve as anchors for the cytoskeleton
linkage between cytoskeleton and EC matrix is responsible for the stability of cell-matrix junctions
distinct interaction between integrins and the cytoskeleton are found at 2 types of cell-matrix junctions:
- focal adhesions
- hemidesmosomes
describe integrin function in focal adhesions
- attach a variety of cells (including fibroblasts) to the EC matrix
- cytoplasmic domains of the integrin beta subunits anchor the actin cytoskeleton by associating with bundles of actin filaments
describe integrin function in hemidesmosomes
- mediate epithelial cell attachments at which the alpha-6-beta-4 integrin is linked to intermediate filaments and laminin (via plectin) → anchors epithelial cells to basal lamina
