Chapter 15: Extracellular Matrix and Cell Interactions

basal laminae

thin layers on which epithelial cells rest, surrounds muscle cells, adipose cells, peripheral nerves

major structural protein

collagen

collagen structure

triple helix consisting of a repeating glycine-X-Y sequence

typical amino acid in the X position for collagen

proline

typical amino acid in the Y position for collagen

hydroxyproline

hydroxyl groups

stabilize the triple helix in collagen by forming hydrogen bonds

most abundant form of collagen

Type 1 collagen

type 1 collagen function

forms collagen fibrils in which the triple helical molecules form regular staggered arrays

covalent cross-links

bonds between side chain residues that help strengthen the fibrils

importance of collagen covalent cross-links in medical science

forms and repairs tissues

type of collagen in brain tissue

type IV collagen

glycosaminoglycans (GAGs)

polysaccharides formed from repeating units of disaccharides; form extracellular matrix gels

fundamental unit of GAGs (except for hyaluronan)

dimers

GAG found in cartilage, brain tissue, and neural tissue

hyaluronan

GAGs found in dermis tissue

dermatan sulfate, keratan sulfate

GAGs found in many different tissues

chondroitin sulfate, heparan sulfate

charge on GAGs due to sulfate groups

highly negative charge

only GAG that is a single long polysaccharide chain

hyaluronan

proteoglycans

formed by GAGs linked to proteins

function of hyaluronan

interacts with proteoglycans to form large complexes in the extracellular matrix

main adhesion protein of connective tissues

fibronectin

molecules for which fibronectin has binding sites

collagen, GAGs, and integrin

adhesion proteins in basal laminae

laminins

laminin structure

3 polypeptide chains, each with rod-like domains interspersed with globular domains, and binding sites on the subunits

structure formed by multiple laminins

networks

adhesion protein that is tightly associated with laminins

nidogen

type of collagen that nidogen binds

type IV collagen

structure of integrin

dimer formed by an α subunit and a ß subunit

number of possible α subunits in integrin

18

number of possible ß subunits in integrin

8

number of different integrins

24

extracellular matrix molecules bound by integrin

collagen, fibronectin, laminin, cytoskeleton

groups of cell adhesion molecules that mediate cell-cell adhesion

selectins, integrins, immunoglobulin (IG) superfamily, cadherins

ligands recognized by selectins

carbohydrates

stable cell junctions formed by selectins

none

ligands recognized by integrins

extracellular matrix, Ig superfamily members

ligands recognized by the Ig superfamily

integrins

ligands recognized by cadherins

cadherins

stable cell junctions formed by integrins

focal adhesions, hemidesmosomes

stable cell junctions formed by Ig superfamily

none

stable cell junctions formed by cadherins

adherens junctions, desmosomes

function of selectins

mediates transient interactions between leukocytes and endothelial cells (or blood platelets)

leukocyte integrins form stable connections with these molecules

intercellular adhesion molecules (ICAMS)

heterophilic interaction

an adhesion molecule on one cell recognizes a different molecule on another cell

example of a heterophilic interaction

binding of ICAMs to integrins

homophilic interaction

an adhesion molecule one one cell binds to the same molecule on another cell

example of a homophilic interaction

binding between neural cell adhesion molecules

cell adhesion molecule that mediates homophilic interactions

cadherin

adherens junctions

cadherins link the actin filaments of one cell to the actin filaments of another

desmosomes

desmoglein and desmocollin link to intermediate filaments of adjacent cells

tight junctions

forms a seal that prevents free passage of molecules and ions between cells, prevents free diffusion of lipids and membrane proteins

junctional complex

tight junctions in association with adherens junctions and desmosomes

gap junctions

open channels through the plasma membrane within a tissue

effect of open gap junctions

ions and small molecules are able to diffuse freely between neighboring cells

connexin family

transmembrane proteins that make up gap junctions

connexon structure

6 connexins form a cylinder with an open aqueous pore in the center

electrical synapse

specialized gap junctions that occur on specific nerve cells

plasmodesmata

cytoplasmic connections through which adjacent plant cells communicate; analogous to gap junctions

formation of plasmodesmata

incomplete separation of daughter cells following mitosis (in plants)

plasmodesmata structure

plasma membrane is continuous between the two cells, creating a channel between the cytosols, with smooth ER connected between the two cells