The Extracellular Matrix of Animal Cells Flashcards
What are the three types of ECM?
Describe them.
Bone - consists largely of a rigid extra cellular matrix that contains a tiny number of interspersed cells
Cartilage - tissue constructed almost entirely of matrix materials, but more flexible than bone
Connective Tissue - surrounding glands and blood vessels has a relatively gelatinous extracellular matrix containing numerous interspersed fibroblast cells
What are the three classes of molecules in the ECM?
- structural proteins such as collagens and elastins, which provide strength and flexibility
- Protein-polysaccharide complexes, proteoglycans, that provide the matrix
- adhesive glycoproteins, fibronectins and lamins, that allow cells to attach to the matrix
- Structural Proteins:
what is collagen?
how does it represent itself in the ECM?
collagen is the most abundant ECM component in animals, occur as a rigid triple helix of intertwined polypeptides
collagens form fibers with high tensile strength
- Structural Proteins
what is procollagen?
a precursor molecule that is converted to collagen by proteolytic cleavage of sequences at both the N- and C- terminus ends.
- Structural Proteins
what is an elastin?
how is an elastin used in the ECM?
a family of ECM proteins what provide elasticity to the ECM
elastin molecules are cross-linked to one another by covalent bonds between lysine residues
- Protein-polysaccharide
Glycosaminoglycans (GAGs)
what are they?
how do they make up the matrix?
large carbohydrates characterized by repeating disaccharide units
most are covalently bound to protein molecules to form proteoglycans
- Protein-polysaccharide
Proteoglycans
how do they make up the matrix?
proteoglycans are integral components of the plasma membrane, with their core polypeptides embedded within the membrane
proteoglycans can also by covalently linked to membrane phospholipids
- Protein polysaccharide
what is hyaluronate?
hyaluronate is a glycosaminoglycan found in high concentration in the extracellular matrix where cells are actively proliferating or migrating, and the joints between moveable bones
- Adhesive glycoproteins
what are fibronectins?
fibronectins are a family of closely related adhesive glycoproteins in the ECM and are widely distributed in vertebrates
fibronectin molecules consist of two very large polypeptide subunits that are linked near their carboxyl ends by a pair of disulfide bonds
- Adhesive glycproteins
what do fibronectin domains bind to?
domains bind to one or more specific kinds of macromolecules located in the ECM or on cell surfaces, including several types of collagen, heparin and the blood clotting protein fibrin
- Adhesive glcoproteins
what are laminins?
laminins are found mainly in the basal lamina
laminins consist of three long polypeptides alpha, beta and gamma combine to form many types of laminins
disulfide bonds hold the polypeptides together in the shape of a cross
- Adhesive glycoproteins
What are MMP’s (matrix metalloproteinases)?
enzymes which require metal ions as cofactors, degrade the ECM locally allowing cells to pass through the ECM (metastasizing cancer cells)
- Adhesive glycoproteins
what are integrins?
the recetors that are on the surface of plasma membranes where laminins and fibronectins can bind to
they INTEGRATE the cytoskeleton with the extracellular matrix
- Adhesive glycoproteins
what are focal adhesions?
migratory and non-epithelial cells attach to the ECM molecule through focal adhesions
the contain clustered integrins that interact with bundles of actin microfilaments via several linker proteins
- Adhesive glycoproteins
what are hemidesmosomes?
they are found in epithelial cells
a major type of integrin-mediated attatchment where in epithelial cells the hemidesmosomes attach to the laminin in the basal lamina
- adhesive glycoproteins
what is anchorage-dependent growth?
requirement that cells be attached to a solid surface such as ECM before they can grow and divide
- adhesive glycoproteins
what are costameres?
what is dystrophin?
an attachment structure at the surface of striated muscle
contain many of the same proteins found at focal contracts in addition to the protein dystrophin
dystrophin is a large protein that interacts with a complex that includes integral membrane protein dystroglycan and the sarcoglycan-sarcospan complexes
- adhesive proteoglycans
what is the glycocalyx?
what are the roles of the glycocalyx?
a carbohydrate rich zone that often surrounds the plasma membrane
- cell adhesion
- recognition
- protection of the surface
- creation of permeability barriers
what do plant cell walls consist of?
mainly of long cellulose microfibrils enmeshed in a network of branched polysaccharides and glycoproteins called extensins
- cellulose
- hemicelluoses
- pectins
- extensins
- lignins
cellulose in the cell wall:
what do they look like?
long, ribbonlike structures that are stabililzed by intramolecular hydrogen bonds
hemicellulose in the cell wall:
what does it look like?
chemically and structurally distinct from cellulose
heterogeneous group of polysaccharides, each consisting of a long, linear chain of a single kind of sugar with short side chains bonded into a rigid network
pectins in the cell wall:
what are pectins?
branched polysaccharides with backbones called rhamnogalacturonans; the side chains have the same monosaccharides found in the hemicellulose
what are extensins?
group of related glycoproteins, which are deposited in soluble form
in the cell wall, extensins become covalently crosslinked to on another and cellulose
what are lignins?
insoluble polymers of aromatic alcohols found mainly in woody tissues
localized between cellulose fibrils
how are cell walls synthesized?
- middle lamella
- primary cell wall which is a loosely organized network of cellulose, hemicellulose, pectins, and glycoproteins
once cells have stopped growing they add a secondary cell wall
what are plasmodesmata?
junctions between plant cells that allow for cell-cell communication and cytoplasmic continuity
