Biology - Chapter 19: Cell Junctions and Extracellular Matrix | Quizlet

extracellular matrix (ECM)

a complex network of proteins and polysaccharide chains that the cells secrete

connective tissues (bone, tendon)

formed from extracellular matrix produced by cells that are distributed sparsely in the matrix

epithelial tissues

cells form sheets called epithelia, ECM is less pronounced (basal lamina)

basal lamina (basement membrane)

thin extracellular layer that lies underneath epithelial cells and separates them from other tissues

anchoring junctions

link cytoskeleton to adjacent cells or ECM (adherens junctions, desmosomes, actin-linked cell-matrix junctions, hemidesmosomes)

adherens junctions

anchorage sites for actin filaments

desmosomes

anchorage sites for intermediate filaments

transmembrane adhesion proteins

mediate anchoring junctions; include cadherins (to other cells) and integrins (to ECM)

classical cadherins

E-cadherin, N-cadherin, P-cadherin

binding of cadherins is

homophilic

high selectivity of cadherins

important for cadherin-dependent cell sorting

mesenchymal cells

Stem cells that differentiate into fibroblasts, macrophages, etc.

epithelial-mesenchymal transitions

epithelial cells change their character, disassemble, and migrate away from their parent epithelium as separate cells

epithelial-mesenchymal transition is regulated by transcription proteins:

Slug, Snail and Twist

p120-catenin

(adherens junction) binds to cytoplasmic tail of cadherin

β-catenin

adaptor protein binding alongside p120 onto the actin filament

α-catenin

(adherens junctions) binding to β-catenin and actin filament

vinculin

connects actin filament to α-catenin

plankoglobin

adaptor protein connecting intermediate filaments and cadherins

Adhesion belts (in adherens junction)

continuous band of membrane proteins

intercalation

loss of adherens junctions to allow new cells to be inserted

tight junctions

prevent leakage of extracellular fluid across a layer of epithelial cells

transmembrane proteins forming tight junctions

claudin (essential), occludin, tricellulin, JAM

key organizational proteins at tight junctions

zonula occludens (ZO) - scaffold proteins with PDZ domains

gap junctions

provide cytoplasmic channels between adjacent animal cells

channel-forming proteins

connexins and innexins

Gap junctions have a pore size of about 1.4 nm, which allows the exchange of

inorganic ions and small water-soluble molecules

connexon

six connexins combined

selectins

cell-surface carbohydrate-binding proteins (lectins) that mediate a variety of momentary cell-cell adhesion interactions in the bloodstream

types of selectin

L-selectin (on white blood cells), P-selectin (on thrombocytes), E-selectin (on activated endothelial cells)

cell adhesion molecules (CAMs)

members of Ig superfamily that are recognized by the white blood cell integrins

ICAM

intercellular adhesion molecule; heterophilic adhesion to integrins

VCAM

vascular cell adhesion molecule; heterophilic adhesion to integrins

NCAM

neural cell adhesion molecule; homophilic binding

fibroblasts

produces proteins and polysaccharides composing the ECM

three major classes of macromolecules composing ECM

1. glycosaminoglycans (GAGs)

2. fibrous proteins (primarily members of collagen family)

3. noncollagen glycoproteins

GAGs (glycosaminoglycans)

unbranched polysaccharide chains composed of repeating disaccharide units (usually N-sugar + uronic acid)

properties of GAGs

strongly hydrophilic, high density of negative charges (attracts osmotically active Na+)

four main groups of GAGs

1. hyaluronan

2. chondroitin sulfate

3. dermatan sulfate

4. keratan sulfate

hyaluronan

simplest of the GAGs, has a role in resisting compressive forces in tissues and joints, a space filler during embryonic development

proteoglycans

proteins to which GAGs covalently bind (all except hyaluronan)

collagens

fibrous glycoproteins found only in the ECM

types of collagen

fibril-forming collagens, fibril-associated, network-forming, transmembrane, proteoglycan core protein

fibril-associated collagens

IX, important in organizing collagen fibrils

fibrillar collagens

I, II, III, V, XI

elastin

protein base similar to collagen (but not glycosilated) that forms elastic tissue

fibronectin

a noncollagen glycoprotein with many binding sites that helps organize the ECM

type III fibronectin repeat

the major repeat domain in fibronectin, which is 90 AA long and occurs at least 15 times in each subunit

RGD sequence

Arg-Gly-Asp

peptides containing RGD sequence can compete with ____ for the binding site on cell (anti-clotting drugs)

fibronectins

structure of basal lamina

laminin, type IV collagen and nidogen with proteoglycan perlecan

laminin

is the protein found in the basement membrane to which integrins from cells attach

degradation of ECM

division of cells, travelling through ECM

proteolytic enzymes degrading ECM

matrix metalloproteases and serine proteases

integrins

membrane proteins that transmit signals between the ECM and cytoskeleton

structure of integrins

two noncovalently associated glycoprotein subunits α and β; short C-terminal tails and large N-terminal extracellular domains

hemidesmosomes

integrins anchor the cell to laminin in basal lamina and to keratin intermediate filament in a cell via adaptor proteins plectin and BP230

active integrin conformation

unhooked, exposing intracellular binding sites, external segments unfold

inactive integrin conformation

intracellular segments are hooked, extracellular segments are folded

outside-in mechanism for integrin activation

binding of an external matrix protein, such as the RGD sequence of fibronectin

inside-out integrin activation

depends on intracellular regulatory signals that stimulate the ability of talin and other proteins to interact with the β chain of the integrin

talin

adaptor protein which competes with the α-subunit of integrin for a binding site on the β-subunit; it mediates the interaction of integrin with actin filaments

anchorage dependence

dependence of cell growth, proliferation and cell survival on attachment to a substratum (mainly mediated by integrins)

FAK (focal adhesion kinase)

a nonreceptor tyrosine kinase that plays a key role in integrin signaling