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BIO CH 14 II
BIO 309 Chapter 14 - extracellular matrix and cell-matrix interactions
| Question | Answer |
|---|---|
| animal cells in tissues are embedded in | an extracellular matrix |
| the various extracellular matrices consist of: | secreted proteins and polysaccharides |
| epithelial cells rest on | basal laminae |
| morphology of basal laminae | thin, sheetlike |
| function of basal laminae | to support layers of epithelial cells and surround muscle cells, adipose cells, and peripheral nerves |
| beneath the basal laminae is ___ | loose connective tissue |
| the loose connective tissue beneath the basal laminae consists largely of | extraceullular matrix secreted by fibroblasts |
| extracellular matrix is most abundant in | connective tissues |
| in many types of connective tissue, the proteins and polysaccharides in the extracellular matrix are | closely associated with the plasma membrane |
| this interaction of extracellular matrix proteins and polysaccharides with the plasma membrane is seen in the ____ | glycocalyx |
| the extracellular matrix is principally responsible for the structure and function of | connective tissue |
| extracellular matrices are composed of ___ embedded in _____ | tough fibrous proteins, gel-like polysaccharide |
| in addition to proteins and polysaccharides, the extracellular matrix contains | adhesion proteins |
| the sheetlike structure of basal laminae results from | a matrix composition that differs from that found in other connective tissues |
| the major structural protein of the extracellular matrix | collagen |
| collagen | major structural protein of the extracellular matrix |
| what is the single most abundant protein in animal tissues? | collagen |
| the collagens are a large family of proteins containing at least ___ members | 28 |
| collagens are characterized by their formation of | triple helices of three polypeptide chains |
| the triple hellix domains of the collagens consist of ___ repeats. | Gly-X-Y |
| a ___ is required every ____ in order for the collagen triple helix to form | Gly, 3rd position |
| what other amino acids are frequently found in the collagen triple helix? | proline, hydroxylproline |
| why are Pro and Hyp found in the collagen triple helix | their ring structure stabilizes the triple helix |
| The amino acid hydroxylproline is formed in the ___ by ____ | ER, modification of proline residues that have already been incorporated into collagen |
| aside from proline, ___ residues in collagen are often converted to ___ | lysines, hydroxylysines |
| where is type I collagen | connective tissue |
| where is type IV collagen | basement membranes |
| what is the most abundant type of collagen | type I |
| how many possible trimers of collagen can be assembled? | 42 |
| the polypeptide chains of type I collagens consist of ___ amino acids | 1000 |
| type I collagens, after secretion from the cell, form ___ | collagen fibrils |
| collagen fibrils | regular staggered arrays of associated collagen triple helices, formed by type I collagen after secretion from the cell |
| how are collagen fibrils stabilized | covalent cross-links between lysine or hydroxylysine |
| collagen fibril formation takes place ___ only | outside the cell |
| why does collagen fibril formation take place outside of the cell only? | the precursors have nonhelical terminal segments that are cleaved after secretion |
| procollagen | the water-soluble precursor to the fibril-forming collagens |
| frequently, the collagen fibrils interact with each other to form | collagen fibers |
| in addition to the fibril-forming collagens, connective tissues contain ______ | fibril-associated collagens |
| fibril-associated collagens function: | bind to collagen fibrils and link them to one another and to other matrix components |
| type IV collagen is ____ interrupted by ____ | Gly-X-Y sequence, multiple nonhelical sequences |
| type IV collagen is ___ collagen | network-forming |
| what types of collagen are network-forming? | IV, VI, XVIII |
| network-forming collagens are more/less flexible than fibril-forming collagens | more |
| network-forming collagens assemble into | 2D cross-linked networks |
| connective tissues also contain ___, abundant in organs that regularly strech and return to original size | elastic fibers |
| elastin fibers are composed mainly of ___, a ____ | elastin, protein |
| elastin is cross-linked by | covalent bonds between the side chains of lysine residues |
| the structural proteins of the extracellular matrix are embedded in gels formed from polysaccharides called | glycosaminoglycans (GAGs) |
| GAGs consist of | repeating units of disaccharides |
| One of the sugars in the repeating disaccharide unit of GAGs is | N-acetylglucosamine or N-acetylgalactosamine |
| The second sugar in the repeating dissacharide unit of GAGs is | usually acidic |
| GAGs are nearly all modified by | addition of sulfate groups |
| GAGs are highly | negatively charged |
| the only GAG that is not sulfated | hyaluronan |
| what are the five major types of GAGs | hyaluronan, dermatan sulfate, chrondroitin sulfate, keratan sulfate, heparan sulfate |
| what is a proteoglycan | a protein linked to glycosaminoglycans |
| hyaluron is synthesized at ____ by ____ | the plasma membrane, transmembrane hyaluronan synthase. |
| GAGs are linked to proteins to form | proteoglycans |
| proteoglycans can consist up to ___% polysaccharide by weight | 95 |
| general structure of a proteoglycan | GAG chains attached to core protein |
| proteoglycans can interact with _____ to form large complexes in the extracellular matrix | hyaluronan |
| the major protein of cartilage | aggrecan |
| aggrecan molecules aggregate with _____ to form large aggregates that become trapped in the collagen matrix. | hyaluronan |
| molecular weight of aggrecan aggregates | >10^6 D |
| the prototype of matrix adhesion proteins | fibronectin |
| fibronectin | the principle adhesion protein of connective tissues |
| weight of fibronectin | 220 kD |
| matrix adhesion proteins are the major binding sites for | integrins |
| structure of fibronectin | dimeric glycoprotein of 2 polypeptide chains |
| each polypeptide chain of fibronectin is ___ long | 2500 amino acids |
| Within the extracellular matrix, fibronectin is often _____ | cross-linked into fibrils |
| Three significant binding sites on fibronectin | cell binding, GAG binding, collagen binding |
| all fibronectin proteins are derived by | alternative splicing of the mRNA of a single gene |
| fibronectin varies greatly/is similar from tissue to tissue | varies greatly |
| How are the two chains of fibronectin joined? | disulfide bonds near the C terminus |
| basal laminae contain distinct adhesion proteins of the ___ family | laminin |
| physical structure of laminins | heterotrimers of a, B, y, subunits |
| laminins are tightly associated with _____, another adhesion protein | entactin |
| entactin binds to type ___ collagen | IV |
| entactin | an extracellular matrix protein that interacts with laminin and the type IV collagen in basal laminae |
| the major cell surface receptors responsible for the attachment of cells to the extracellular membrane | integrins |
| integrins are composed of | two subunits |
| integrins bind to _____ in the _____ | short amino acid sequences, components of the extracellular matrix |
| how many different a subunits of integrins exist | 18 |
| how many different B subunits of integrins exist | 8 |
| how many total possibilities exist for integrins? | 24 |
| two functions of integrins | 1) attaching cells to cellular matrix 2)anchoring the cytoskeleton |
| what interactions occur at cell-matrix junctions? | focal adhesions and hemidesmosomes |
| focal adhesions attach | cells to the extacellular matrix |
| focal adhesions attach the _______ to the e. matrix | actin cytoskeleton |
| hemidesmosomes attach ____ to the e. matrix | intermediate filaments |
| focal adhesions form from | focal complexes |
| focal complexes | cluster of integrins that develops into the focal adhesion |
| focal complexes recruit ___ and ___, which leads to ______ | formin, myosin II, the development of tension |
| focal adhesions can be stable, as in ___, or rapidly turning over, as in ____ | tissues, cell movement |
| during cell migration, the formation of ____ at the leading edge results in _____ at the trailing edge, leading to _____ | focal adhesions, loss of tension, inactivation of integrin binding |
| the ability of integrins to reversibly bind matrix components is dependent on | their ability to change conformation between active and inactive state |
| in the inactive state, integrins are unable to bind to e. matrix because | their ligand binding head group is held close to the cell surface |
| what changes the conformation of integrins to the active state | signals from the cytosol vio talin or vinculin |
| the activaiton of integrin to the active state results in | conveying a signal to the cytosol to respond to integrin binding and recruit more integrins |
| hyaluronan is the only GAG that occurs as | a single long polypeptide chain |
| all GAGs form | proteoglycans |
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