Cell$Connec(ons$$Last$class:$$Cell$cycle$(control(of(growth,(replica2on,(and(division)(h7p://www.youtube.com/watch?v=QGx50C1w8YY(Remember:$$Review$the$similari(es$and$differences$between$Mitosis$and$Meiosis$h7ps://www.youtube.com/watch?v=rqPMp0U0HOA(Figure 19-1 Molecular Biology of the Cell (© Garland Science 2008) Today:$$Cell-cell$&$cell-matrix$connec(ons(Animal(cells(can(be(organized(into(2ssues.((Five(major(2ssue(types(are:((epithelial,(connec2ve,(muscle,(nervous,(and(blood.(Cells(in(2ssues(interact(with(one(another(and(with(the(extracellular(environment.(These(connec2ons(are(important(for(allowing(cells(to(aggregate(into(dis2nct(2ssues(and(for(the(bi-direc2onal(transfer(of(informa2on(between(the(exterior(and(interior(of(cells.(This(communica2on(is(crucial(for(many(biological(processes(including(cell(survival,(prolifera2on,(differen2a2on,(and(migra2on.((We(will(focus(on(migra2on(next(lecture.)((fibroblast$F-ac2n(Overview$of$some$important$connec(ons(Cells(in(2ssues(can(adhere(directly(to(one(another((cell-cell(adhesion)(through(transmembrane(proteins(called(cell$adhesion$molecules$(CAMs).((Cells(in(2ssues(can(associate(indirectly((cell-matrix(adhesion)(through(binding(of(transmembrane(adhesion$receptors$to(components(of(the(extracellular$matrix$(ECM).((The(ECM(is(a(complex(meshwork(of(proteins(and(polysaccharides(secreted(by(cells(into(extracellular(spaces.(IFs(Figure 19-3 Molecular Biology of the Cell (© Garland Science 2008) Cell$adherence$is$mediated$by$many$different$macromolecular$structures(Several(of(the(most(important(sites(of(cell(adhesion(are((ght$junc(ons,(adherens$junc(ons,(desmosomes,(gap$junc(ons,(hemi-desmosomes,(and(focal$adhesions$(focal(contacts).(Table 19-1 Molecular Biology of the Cell (© Garland Science 2008) Summary$of$some$different$cell$connec(ons((later)$(focal$adhesions)$Cell-cell$adhesions$involve$cis$(same$side)$and$trans$(opposite$side)$interac(ons(Cell(adhesion(molecules((CAMs)(can(generate(very(2ght(adhesion(when(many(weak(interac2ons(are(combined(–(like(velcro.(Major$families$of$cell$adhesion$molecules$(CAMs)$(Figure 19-8 Molecular Biology of the Cell (same(CAM(on(both(cells)((different(CAM(classes)(Cellular(adhesions(are(controlled(by(homophilic(and(heterophilic(interac2ons.(Cadherins(form(homophilic(cross-bridges(between(adjacent(cells.(Integrins(can(func2on(as(CAMs((not(shown)(but(are(best(known(as(adhesion$receptors$that(bind(to(large(mul2-adhesive(ECM(proteins(such(as(fibronec2n.(Cell-cell$interac(ons$at$adherens$junc(ons$and$desmosomes$are$mediated$by$cadherins(Cadherins((calcium-adhering(proteins)(form(extracellular(cross-bridges(between(adjacent(cells.(At(adherens$junc(ons,(cadherins(are(linked(indirectly(to(intracellular(ac2n(filaments(via(cytoskeletal(adapter(proteins(called(catenins.(At(desmosomes,(cadherins(are(linked(indirectly(to(intermediate(filaments.(Cadherins(play(key(roles(in(2ssue(differen2a2on,(as(they(effect(cell-cell(adhesion(and(cell(migra2on((e.g.,(during(EMT-(the(epithelial-mesenchymal(transi2on).(The(adhesiveness(of(cadherins((as(their(name(indicates)(is(dependent(on(extracellular(calcium.(Vertebrates(express(more(than(100(cadherins.(Table 19-3 Molecular Biology of the Cell (© Garland Science 2008)
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